Chapter 5: Pasteurized Fish and Fishery Products

• Potential Food Safety Hazard
• Control Measures
• FDA Guidelines
• State Guidelines
• South Carolina: Blue crab (Callinectes sapidus)
• Texas: Blue crab (Callinectes sapidus)
• Process Establishment
• Critical Aspects of Processes
• Analytical Procedures
• Thermometer calibration
• Direct microscopic examination of foods (except eggs) - Gram stain
• Examination of canned foods
• Headspace gas determination by gas-liquid chromatography
• Modification of headspace gas analysis methodology, using the SP4270 integrator
• Examination of metal containers for integrity
• Examination of glass containers for integrity
• Examination of flexible and semirigid food containers for integrity
• Container integrity glossary
• Other analytical procedures
• Pasteurizing Processes
• References

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Potential Food Safety Hazard

Selection of the target pathogen is critical. If a target pathogen other than C. botulinum type E is selected, you must consider the potential that C. botulinum type E or other relatively heat tolerant pathogens will survive the pasteurization process and grow under normal storage conditions or moderate abuse conditions. For example, vacuum packaged lobster meat that is pasteurized to kill L. monocytogenes but not C. botulinum type E must be frozen to prevent C. botulinum type E growth and toxin formation (FDA, 1998b; FDA, 1998c; Rippen, 1998).

The pasteurization of blue crabmeat involves heating products in hermetically sealed packaging to achieve a minimum cumulative heat exposure of = 31 min, followed by refrigerated storage. If less heat exposure or non-hermetic packaging is used, the products are not considered pasteurized and, generally, must be frozen (NBCIA, 1993). Under special HACCP controls, sealed, refrigerated minimally processed products (e.g., sous vide items) may be permitted. Seek regulatory input prior to producing these kinds of products (Rippen, 1998).

The introduction of pathogens after pasteurization can cause consumer illness. In addition to eliminating pathogens, the pasteurization process also greatly reduces the number of spoilage bacteria present in the fishery product. These bacteria normally restrict the growth of pathogens through competition. Rapid growth of pathogens introduced after pasteurization is, therefore, a concern (FDA, 1998b; FDA, 1998c).

Note: D-values and F-values are discussed in chapter 3.

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Control Measures

There are two primary causes of recontamination after pasteurization. They are:

• Defective container closures; and
• Contaminated container-cooling water.

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FDA Guidelines

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State Guidelines

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South Carolina: Blue crab (Callinectes sapidus)

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Texas: Blue crab (Callinectes sapidus)

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Process Establishment

Because of the variability inherent in water bath pasteurization systems, process establishment studies are usually performed initially for each container size and shape, and when equipment or procedures are modified. Generally, a process authority will compare these results to published heat sensitivity values for C. botulinum and other relevant pathogens when setting minimum process schedules. If conditions change in the design or operation of the equipment, or if another product container is selected, verification studies must be performed.

Process authorities commonly establish minimum pasteurization processes by generating heating profiles at the slowest heating point (cold point) of the product. Monitored containers are positioned throughout the pasteurization tank/chamber. Specialized instrumentation is required for this. These heating profiles are then used to determine process lethality, or the calculated effect of all heat exposure on a target microorganism. Commonly, this is achieved by determining an F-value for the slowest heating container in the system (Hackney et al., 1991; Rippen, 1998).

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Critical Aspects of Processes

• Length of the pasteurization cycle (speed of the belt for a continuous pasteurizer);
• Temperature of the water bath;
• Water bath circulation;
• Product initial temperature (I.T.);
• Container size (e.g., can dimensions, pouch thickness);
• Product formulation;
• Container integrity;
• Microbial quality of cooling water;
• Accuracy of thermometers, recorder thermometer charts, high temperature alarms, maximum indicating thermometers, and/or digital data loggers; and
• Accuracy of other monitoring and timing instruments

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Analytical Procedures

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Thermometer calibration

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Direct Microscopic Examination of Foods (Except Eggs) - Gram Stain (Bryce and Poelma, 1998)

1. Equipment and materials
1. Glass slides, 25 ´ 75 mm, with etched portion for labeling; 1 slide for each blended food sample (10^-1 dilution)
2. Wire loop, 3-4 mm, platinum-iridium or nichrome, B&S gauge No. 24 or 26
3. Gram stain
1. Hucker's crystal violet
• Solution A: Crystal violet (90% dye content), 2 g; Ethanol, 95%, 20 ml
• Solution B: Ammonium oxalate, 0.8 g; Distilled water, 80 ml.
• Mix solutions A and B. Store 24 h and filter through coarse filter paper.
2. Gram's iodine
• Iodine, 1 g; Potassium iodide (KI), 2 g; Distilled water, 300 ml.
• Place KI in mortar, add iodine, and grind with pestle for 5-10 s. Add 1 ml water and grind; then add 5 ml of water and grind, then 10 ml and grind. Pour this solution into reagent bottle. Rinse mortar and pestle with amount of water needed to bring total volume to 300 ml.
3. Hucker's counterstain
• Stock solution: Safranin O (certified), 2.5; Ethanol, 95%, 100 ml
• Working solution: Add 10 ml stock solution to 90 ml distilled water.
4. Microscope, with oil immersion objective lens (95-100X) and 10X ocular
5. Immersion oil
6. Methanol
7. Xylene
2. Procedure

Prepare film of blended food sample (10^-1 dilution). Air-dry films and fix with moderate heat by passing films rapidly over Bunsen or Fisher burner flame 3 or 4 times. Alternatively, air-dry films and fix with methanol 1-2 min, drain excess methanol, and flame or air-dry (this is particularly helpful for foods with a high sugar content). Cool to room temperature before staining. De-fat films of food with high fat content by immersing films in xylene 1-2 min; then drain, wash in methanol, drain, and dry.

Stain films 1 min with crystal violet-ammonium oxalate solution. Wash briefly in tap water and drain. Apply Gram's iodine for 1 min. Wash in tap water and drain.

Decolorize with 95% ethanol until blue color is no longer released (about 30 s). Alternatively, flood slides with ethanol, pour off immediately, and reflood with ethanol for 10 g. Wash briefly with water, drain, and apply Hucker's counterstain (safranin solution) for 10-30 g. Wash briefly with water, drain, blot or air-dry, and examine.

Use microscope equipped with oil immersion objective (95-100X) and 10X ocular; adjust lighting systems to Koehlor illumination. Examine at least 10 fields of each film, noting predominant types of organisms, especially clostridial forms, Gram-positive cocci, and Gram-negative bacilli.

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Examination of Canned Foods (Landry et al., 1998)

The incidence of spoilage in canned foods is low, but when it occurs it must be investigated properly. Swollen cans often indicate a spoiled product. During spoilage, cans may progress from normal to flipper, to springer, to soft swell, to hard swell. However, spoilage is not the only cause of abnormal cans. Overfilling, buckling, denting, or closing while cool may also be responsible. Microbial spoilage and hydrogen, produced by the interaction of acids in the food product with the metals of the can, are the principal causes of swelling. High summer temperatures and high altitudes may also increase the degree of swelling. Some microorganisms that grow in canned foods, however, do not produce gas and therefore cause no abnormal appearance of the can; nevertheless, they cause spoilage of the product.

Spoilage is usually caused by growth of microorganisms following leakage or underprocessing. Leakage occurs from can defects, punctures, or rough handling. Contaminated cooling water sometimes leaks to the interior through pinholes or poor seams and introduces bacteria that cause spoilage. A viable mixed microflora of bacterial rods and cocci is indicative of leakage, which may usually be confirmed by can examination. Underprocessing may be caused by undercooking; retort operations that are faulty because of inaccurate or improperly functioning thermometers, gauges, or controls; excessive contamination of the product for which normally adequate processes are insufficient; changes in formulation or handling of the product that result in a more viscous product or tighter packing in the container, with consequent lengthening of the heat penetration time; or, sometimes, accidental bypassing of the retort operation altogether. When the can contains a spoiled product and no viable microorganisms, spoilage may have occurred before processing or the microorganisms causing the spoilage may have died during storage.

Underprocessed and leaking cans are of major concern and both pose potential health hazards. However, before a decision can be made regarding the potential health hazard of a low-acid canned food, certain basic information is necessary. Naturally, if Clostridium botulinum (spores, toxin, or both) is found, the hazard is obvious. Intact cans that contain only mesophilic, Gram-positive, sporeforming rods should be considered underprocessed, unless proved otherwise. It must be determined that the can is intact (commercially acceptable seams and no microleaks) and that other factors that may lead to underprocessing, such as drained weight and product formulation, have been evaluated.

The preferred type of tool for can content examination is a bacteriological can opener consisting of a puncturing device at the end of a metal rod mounted with a sliding triangular blade that is held in place by a set screw. The advantage over other types of openers is that it does no damage to the double seam and therefore will not interfere with subsequent seam examination of the can.

The number of cans examined bacteriologically should be large enough to give reliable results. When the cause of spoilage is clear-cut, culturing 4-6 cans may be adequate, but in some cases it may be necessary to culture 10-50 cans before the cause of spoilage can be determined. On special occasions these procedures may not yield all the required information, and additional tests must be devised to collect the necessary data. Unspoiled cans may be examined bacteriologically to determine the presence of viable but dormant organisms. The procedure is the same as that used for spoiled foods except that the number of cans examined and the quantity of material subcultured must be increased.

1. Equipment and materials
1. Incubators, thermostatically controlled at 30, 35, and 55ºC (86, 95, and 131ºF)
2. pH meter, potentiometer
3. Microscope, slides, and coverslips
4. Can opener, bacteriological can opener, and can punch, all sterile
5. Petri dishes, sterile
6. Test tubes, sterile
7. Serological pipets, cotton-plugged, sterile
8. Nontapered pipets, cotton-plugged (8 mm tubing), sterile
9. Soap, water, brush, and towels, sterile and nonsterile
10. Indelible ink marking pen
11. Diamond point pen for marking cans
12. Examination pans (Pyrex or enamel baking pans)
2. Media and reagents

Codes, e.g., "M27" refer to media recipes in the FDA Bacteriological Analytical Manual (Merker, 1998).
 
1. Bromcresol purple (BCP) dextrose broth (M27)
2. Chopped liver broth (M38) or cooked meat medium (CMM) (M42)
3. Malt extract broth (M94)
4. Liver-veal agar (without egg yolk) (LVA) (M83)
5. Acid broth (M4)
6. Nutrient agar (NA) (M112)
7. Methylene blue stain (R45), crystal violet (R16), or Gram stain (R32)
8. Sabouraud's dextrose agar (SAB) (M133)
9. 4% Iodine in 70% ethanol (R18)
3. Can preparation

Remove labels. With marking pen, transfer subnumbers to side of can to aid in correlating findings with code. Mark labels so that they may be replaced in their original position on the can to help locate defects indicated by stains on label. Separate all cans by code numbers and record size of container, code, product, condition, evidence of leakage, pinholes or rusting, dents, buckling or other abnormality, and all identifying marks on label. Classify each can according to the descriptive terms in Table 5-1. Before observing cans for classification, make sure cans are at room temperature.

Table 5-1. Useful descriptive terms for canned food analysis.

Exterior can condition  leaker  dented  rusted  buckled  paneled  bulge		Internal can condition normal peeling slight, moderate or severe etching slight, moderate or severe blackening slight, moderate or severe rusting mechanical damage
Micro-leak test packer seam  side panel  side seam  cut code  pinhole		Product odor putrid acidic butyric  metallic sour cheesy fermented musty sweet fecal sulfur off-odor	Product liquor cloudy clear foreign frothy
Solid product digested  softened  curdled  uncooked  overcooked	Liquid product cloudy clear foreign frothy	Pigment darkened light changed	Consistency slimy fluid viscous ropy
Flat - a can with both ends concave; it remains in this condition even when the can is brought down sharply on its end on a solid, flat surface.
Flipper - a can that normally appears flat; when brought down sharply on its end on a flat surface, one end flips out. When pressure is applied to this end, it flips in again and the can appears flat.
Springer - a can with one end permanently bulged. When sufficient pressure is applied to this end, it will flip in, but the other end will flip out.
Soft swell - a can bulged at both ends, but not so tightly that the ends cannot be pushed in somewhat with thumb pressure.
Hard swell - a can bulged at both ends, and so tightly that no indentation can be made with thumb pressure. A hard swell will generally "buckle" before the can bursts. Bursting usually occurs at the double seam over the side seam lap, or in the middle of the side seam.

4. Examination of can and contents

Classification of cans. NOTE : Cans must be at room temperature for classification.

1. Sampling can contents
1. Swollen cans . Immediately analyze springers, swells, and a representative number (at least 6, if available) of flat and flipper cans. Retain examples of each, if available, when reserve portion must be held. Place remaining flat and flipper cans (excluding those held in reserve) in incubator at 35ºC (95ºF). Examine at frequent intervals for 14 d. When abnormal can or one becoming increasingly swollen is found, make note of it. When can becomes a hard swell or when swelling no longer progresses, culture sampled contents, examine for preformed toxin of C. botulinum if microscopic examination shows typical C. botulinum organisms or Gram-positive rods, and perform remaining steps of canned food examination.
2. Flat and flipper cans . Place cans (excluding those held in reserve) in incubator at 35ºC (95ºF). Observe cans for progressive swelling at frequent intervals for 14 d. When swelling occurs, follow directions in l-a, above. After 14 d remove flat and flipper cans from incubator and test at least 6, if available. (It is not necessary to analyze all normal cans.) Do not incubate cans at temperatures above 35ºC (95ºF). After incubation, bring cans back to room temperature before classifying them.

2. Opening the can . Open can in an environment that is as aseptic as possible. Use of vertical laminar flow hood is recommended.
1. Hard swells, soft swells, and springers . Chill hard swells in refrigerator before opening. Scrub entire uncoded end and adjacent sides of can using abrasive cleanser, cold water, and a brush, steel wool, or abrasive pad. Rinse and dry with clean sterile towel. Sanitize can end to be opened with 4% iodine in 70% ethanol for 30 min and wipe off with sterile towel. DO NOT FLAME . Badly swollen cans may spray out a portion of the contents, which may be toxic. Take some precaution to guard against this hazard, e.g., cover can with sterile towel or invert sterile funnel over can. Sterilize can opener by flaming until it is almost red, or use separate presterilized can openers, one for each can. At the time a swollen can is punctured, test for headspace gas, using a qualitative test or the gas-liquid chromatography method described below. For a qualitative test, hold mouth of sterile test tube at puncture site to capture some escaping gas, or use can-puncturing press to capture some escaping gas in a syringe. Flip mouth of tube to flame of Bunsen burner. A slight explosion indicates presence of hydrogen. Immediately turn tube upright and pour in a small amount of lime water. A white precipitate indicates presence of CO₂. Make opening in sterilized end of can large enough to permit removal of sample.
2. Flipper and flat cans . Scrub entire uncoded end and adjacent sides of can using abrasive cleanser, warm water, and a brush, steel wool, or abrasive pad. Rinse and dry with clean sterile towel. Gently shake cans to mix contents before sanitizing. Flood end of can with iodine-ethanol solution and let stand at least 15 min. Wipe off iodine mixture with clean sterile towel. Ensure sterility of can end by flaming with burner in a hood until iodine-ethanol solution is burned off, end of can becomes discolored from flame, and heat causes metal to expand. Be careful not to inhale iodine fumes while burning off can end. Sterilize can opener by flaming until it is almost red, or use separate presterilized can openers for each can. Make opening in sterilized end of can large enough to permit removal of sample.

3. Removal of material for testing. Remove large enough portions from center of can to inoculate required culture media. Use sterile pipets, either regular or wide-mouthed. Transfer solid pieces with sterile spatulas or other sterile devices. Always use safety devices for pipetting. After removal of inocula, aseptically transfer at least 30 ml or, if less is available, all remaining contents of cans to sterile closed containers, and refrigerate at about 4ºC (39.2ºF). Use this material for repeat examination if needed and for possible toxicity tests. This is the reserve sample. Unless circumstances dictate otherwise, analyze normal cans submitted with sample organoleptically and physically (see E-2, below), including pH determination and seam teardown and evaluation. Simply and completely describe product appearance, consistency, and odor on worksheet. If analyst is not familiar with decomposition odors of canned food, another analyst, preferably one familiar with decomposition odors, should confirm this organoleptic evaluation. In describing the product in the can, include such things as low liquid level (state how low), evidence of compaction, if apparent, and any other characteristics that do not appear normal. Describe internal and external condition of can, including evidence of leakage, etching, corrosion, etc.
4. Physical examination . Perform net weight determinations on a representative number of cans examined (normal and abnormal). Determine drained weight, vacuum, and headspace on a representative number of normal-appearing and abnormal cans (AOAC, 1990). Examine metal container integrity of a representative number of normal cans and all abnormal cans that are not too badly buckled for this purpose (seeExamination of Containers for Integrity ). CAUTION : Always use care when handling the product, even apparently normal cans, because botulinal toxin may be present.
5. Cultural examination of low-acid food (pH greater than 4.6) . If there is any question as to product pH range, determine pH of a representative number of normal cans before proceeding. From each container, inoculate 4 tubes of chopped liver broth or cooked meat medium previously heated to 100ºC (212ºF) (boiling) and rapidly cooled to room temperature; also inoculate 4 tubes of bromcresol purple dextrose broth. Inoculate each tube with 1-2 ml of product liquid or product-water mixture, or 1-2 g of solid material. Incubate as in Table 5-2.

Table 5-2. Incubation times for various media for examination of low acid foods (pH > 4.6).

Medium	No. of tubes	Temp. (ºC)	Time of incubation (h)
Chopped liver   (cooked meat)	2	35	96-120
Chopped liver (cooked meat)	2	55	24-72
Bromcresol purple dextrose broth	2	55	24-48
Bromcresol purple dextrose broth	2	35	96-120

After culturing and removing reserve sample, test material from cans (other than those classified as flat) for preformed toxins of C. botulinum when appropriate, as described in Chapter 12.
1. Microscopic examination . Prepare direct smears from contents of each can after culturing. Dry, fix, and stain with methylene blue, crystal violet, or Gram stain. If product is oily, add xylene to a warm, fixed film, using a dropper; rinse and stain. If product washes off slide during preparation, examine contents as wet mount or hanging drop, or prepare suspension of test material in drop of chopped liver broth before drying. Check liver broth before use to be sure no bacteria are present to contribute to the smear. Examine under microscope; record types of bacteria seen and estimate total number per field.
2. Physical and organoleptic examination of can contents. After removing reserve sample from can, determine pH of remainder, using pH meter. DO NOT USE pH PAPER. Pour contents of cans into examination pans. Examine for odor, color, consistency, texture, and overall quality. DO NOT TASTE THE PRODUCT. Examine can lining for blackening, detinning, and pitting.
5. Cultural findings in cooked meat medium (CMM) and bromcresol purple dextrose broth (BCP)

Check incubated medium for growth at frequent intervals up to maximum time of incubation (Table 5-2). If there is no growth in either medium, report and discard. At time growth is noted, streak 2 plates of liver-veal agar (without egg yolk) or nutrient agar from each positive tube. Incubate one plate aerobically and one anaerobically, as in schematic diagram (Table 5-3). Reincubate CMM at 35ºC (95ºF) for maximum of 5 d for use in future toxin studies. Pick representatives of all morphologically different types of colonies into CMM and incubate for appropriate time, i.e., when growth is sufficient for subculture. Dispel oxygen from CMM broths to be used for anaerobes but not from those to be used for aerobes. After obtaining pure isolates, store cultures to maintain viability.

 
1. If mixed microflora is found only in BCP , report morphological types. If rods are included among mixed microflora in CMM, test CMM for toxin, as described in Chapter 12. If Gram-positive or Gram-variable rods typical of either Bacillus or Clostridium organisms are found in the absence of other morphological types, search to determine whether spores are present. In some cases, old vegetative cells may appear to be Gram-negative and should be treated as if they are Gram-positive. Test culture for toxin according to Chapter 12 .
2. If no toxin is present , send pure cultures for evaluation of heat resistance to Cincinnati District Office, FDA, 1141 Central Parkway, Cincinnati, OH 45202, if cultures meet the following criteria:
• Cultures come from intact cans that are free of leaks and have commercially acceptable seams. (Can seams of both ends of can must be measured; visual examination alone is not sufficient.)

• Two or more tubes are positive and contain similar morphological types.

Maintain a duplicate of each culture. Send obligate anaerobic isolates to Warren Landry, Dallas District Office, FDA, 3032 Bryan Street, Dallas, TX 75204, for further identification.
3. Examination of acid foods (pH 4.6 and below) by cultivation . From each can, inoculate 4 tubes of acid broth and 2 tubes of malt extract broth with 1-2 ml or 1-2 g of product, using the same procedures as for low-acid foods, and incubate as in Table 5-4. Record presence or absence of growth in each tube, and from those that show evidence of growth, make smears and stain. Report types of organisms seen. Pure cultures may be isolated as shown in Table 5-5.

Table 5-3.Schematic diagram of culture procedure for low-acid canned foods

Original Media & Temperature		Subculture		Pure culture		Characterization
CMM and BCP  35ºC (95ºF)		LVA, NAa  Aerobic  Incubate  35ºC (95ºF)	growth	Agar slant  CMM  35ºC (95ºF)		Gram stain  LVA, NA  Anaerobic  35ºC (95ºF)
		LVA, NA  Anaerobic  incubate  35ºC (95ºF)	growth	CMM  35ºC (95ºF)	Gram stain	LVA, NA  Aerobic  35ºC (95ºF)
CMM and BCP  55ºC (131ºF)		LVA, NAa  Aerobic  Incubate  55ºC (131ºF)	growth	Agar slant  CMM  55ºC (131ºF)		Gram stain  LVA, NA  Anaerobic  55ºC (131ºF)
		LVA, NA  Anaerobic  incubate  55ºC (131ºF)	growth	CMM  55ºC (131ºF)	Gram stain	LVA, NA  Aerobic  55ºC (131ºF)

^aLVA, liver-veal agar; NA, nutrient agar; CMM, cooked meat medium; BCP, bromcresol purple dextrose broth.

Table 5-4. Incubation of acid broth and malt extract broth used for acid foods (pH £4.6).

Medium	No. of Tubes	Temp. (ºC)	Time of Incubation (h)
Acid broth	2	55	48
Acid broth	2	30	96
Malt extract broth	2	30	96

Table 5-5. Pure culture scheme for acid foods (pH £ 4.6).

Original Media		Subculture		Pure culture		Characterization
Acid broth  Malt extract broth  30ºC (86ºF)		NA, SABa  Aerobic  30ºC (86ºF)	growth	Agar slant  Acid broth  Malt extract broth  30ºC (86ºF)		Gram stain   NA, SAB  Anaerobic 30ºC
		NA, SABa  Anaerobic  30ºC (86ºF)	growth	Acid broth  Malt extract broth  30ºC (86ºF)	Gram stain	NA, SAB  aerobic
Acid broth  55ºC (131ºF)		NA  Aerobic  55ºC (131ºF)	growth	Agar slant  Acid broth  55ºC (131ºF)		Gram stain  NA  Anaerobic, 55ºC (131ºF)
		NA  Anaerobic  55ºC (131ºF)	growth	Acid broth  55ºC (131ºF)	Gram stain	NA  Aerobic  55ºC (131ºF)

^aNA, nutrient agar; SAB, Sabouraud's dextrose agar.

6. Interpretation of results (see Tables 5-6 to 5-11)
1. The presence of only sporeforming bacteria, which grow at 35ºC (95ºF), in cans with satisfactory seams and no microleaks indicates underprocessing if their heat resistance is equal to or less than that of C. botulinum. Spoilage by thermophilic anaerobes such as C. thermobutylicum may be indicated by gas in cooked meat at 55ºC (131ºF) and a cheesy odor. Spoilage by C. botulinum, C. sporogenes, or C. perfringens may be indicated in cooked meat at 35ºC (95ºF) by gas and a putrid odor; rods, spores, and clostridial forms may be seen on microscopic examination. Always test supernatants of such cultures for botulinal toxin even if no toxin was found in the product itself, since viable botulinal spores in canned foods indicate a potential public health hazard, requiring recall of all cans bearing the same code. Spoilage by mesophilic organisms such as Bacillus thermoacidurans or B. coagulans and/or thermophilic organisms such as B. stearothermophilus, which are flat-sour types, may be indicated by acid production in BCP tubes at 35 and/or 55ºC (95 and/or 131ºF) in high-acid or low-acid canned foods. No definitive conclusions may be drawn from inspection of cultures in broth if the food produced an initial turbidity on inoculation. Presence or absence of growth in this case must be determined by subculturing.
2. Spoilage in acid products is usually caused by nonsporeforming lactobacilli and yeasts. Cans of spoiled tomatoes and tomato juice remain flat but the products have an off-odor, with or without lowered pH, due to aerobic, mesophilic, and thermophilic sporeformers. Spoilage of this type is an exception to the general rule that products below pH 4.6 are immune to spoilage by sporeformers. Many canned foods contain thermophiles which do not grow under normal storage conditions, but which grow and cause spoilage when the product is subjected to elevated temperatures (50-55ºC; 122-131ºF). B. thermoacidurans and B. stearothermophilus are thermophiles responsible for flat-sour decomposition in acid and low-acid foods, respectively. Incubation at 55ºC (131ºF) will not cause a change in the appearance of the can, but the product has an off-odor with or without a lowered pH. Spoilage encountered in products such as tomatoes, pears, figs, and pineapples is occasionally caused by C. pasteurianum, a sporeforming anaerobe which produces gas and a butyric acid odor. C. thermosaccolyticum is a thermophilic anaerobe which causes swelling of the can and a cheesy odor of the product. Cans which bypass the retort without heat processing usually are contaminated with nonsporeformers as well as sporeformers, a spoilage characteristic similar to that resulting from leakage.
3. A mixed microflora of viable bacterial rods and cocci usually indicates leakage. Can examination may not substantiate the bacteriological findings, but leakage at some time in the past must be presumed. Alternatively, the cans may have missed the retort altogether, in which case a high rate of swells would also be expected.
4. A mixed microflora in the product, as shown by direct smear, in which there are large numbers of bacteria visible but no growth in the cultures, may indicate precanning spoilage. This results from bacterial growth in the product before canning. The product may be abnormal in pH, odor, and appearance.
5. If no evidence of microbial growth can be found in swelled cans, the swelling may be due to development of hydrogen by chemical action of contents on container interiors. The proportion of hydrogen varies with the length and condition of storage. Thermophilic anaerobes produce gas, and since cells disintegrate rapidly after growth, it is possible to confuse thermophilic spoilage with hydrogen swells. Chemical breakdown of the product may result in evolution of carbon dioxide. This is particularly true of concentrated products containing sugar and some acid, such as tomato paste, molasses, mincemeats, and highly sugared fruits. The reaction is accelerated at elevated temperatures.
6. Any organisms isolated from normal cans that have obvious vacuum and normal product but no organisms in the direct smear should be suspected as being a laboratory contaminant. To confirm, aseptically inoculate growing organism into another normal can, solder the hole closed, and incubate 14 d at 35ºC (95ºF). If any swelling of container or product changes occur, the organism was probably not in the original sample. If can remains flat, open it aseptically and subculture as previously described. If a culture of the same organism is recovered and the product is normal, consider the product commercially sterile since the organism does not grow under normal conditions of storage and distribution. If you have questions regarding this recommendation, please call Meredith Grahn at (301) 433-3320.

Table 5-6. Classification of food products according to acidity.

Low acid-pH greater than 4.6	Acid-pH 4.6 and below
Meats Seafoods Milk Meat and vegetable mixtures and specialties Spaghetti Soups Vegetables Asparagus Beets Pumpkin Green beans Corn Lima beans	Tomatoes Pears Pineapple Other fruit Sauerkraut Pickles Berries Citrus Rhubarb

Table 5-7. Spoilage microorganisms that cause high and low acidity in various vegetables and fruits.

Spoilage Type	pH Groups	Examples
Thermophilic
Flat-sour	³ 5.3	Corn, peas
Thermophilica	³ 4.8	Spinach, corn
Sulfide spoilagea	³ 5.3	Corn, peas
Mesophilic
Putrefactive anaerobesa	³ 4.8	Corn, asparagus
Butyric anaerobes	³ 4.0	Tomatoes, peas
Aciduric flat-soura	³ 4.2	Tomato juice
Lactobacilli	4.5-3.7	Fruits
Yeasts	£ 3.7	Fruits
Molds	£ 3.7	Fruits

^aThe responsible organisms are bacterial sporeformers.

Table 5-8. Spoilage manifestations in low-acid products.

Group of Organisms	Classification	Manifestation
Flat-sour	Can flat	Possible loss of vacuum on storage
	Product	Appearance not usually altered; pH markedly lowered, sour; may have slightly abnormal odor; sometimes cloudy liquor
Thermophilic anaerobe	Can swells	May burst
	Product	Fermented, sour, cheesy, or butyric odor
Sulfide spoilage	Can flat	H2S gas absorbed by product
	Product	Usually blackened; rotten egg odor
Putrefactive anaerobe	Can swells	May burst
	Product	May be partially digested; pH slightly above normal; typical putrid odor
Aerobic sporeformers	Can flat or swollen	Usually no swelling, except in cured meats when nitrate and sugar present; coagulated evaporated milk, black beets

Table 5-9. Spoilage manifestations in acid products.

Type of Organism	Classification	Manifestation
Bacillus thermoacidurans	Can flat	Little change in vacuum
(flat, sour tomato juice)	Product	Slight pH change; off-odor
Butyric anaerobes	Can swells	May burst
(tomatoes and tomato juice)	Product	Fermented, butyric odor
Nonsporeformers  (mostly lactic types)	Can swells  Product	Usually burst, but swelling may be arrested  Acid odor

Table 5-10. Laboratory diagnosis of bacterial spoilage.

	Underprocessed	Leakage
Can	Flat or swelled; seams generally normal	Swelled; may show normal defectsa
Product  Appearance	Sloppy or fermented	Frothy fermentation; viscous
Odor	Normal, sour or putrid, but generally consistent from can to can	Sour, fecal; generally varying from can to can
pH	Usually fairly constant	Wide variation
Microscopic	Cultures show sporeforming rods only	Mixed cultures
Cultural	Growth at 35 and/or 55ºC (95 and/or 131ºF). May be generally rods and cocci; growth only at characteristic on special media; e.g., usual temperatures acid agar for tomato juice. If product misses retort completely, rods, cocci, yeast or molds, or any combination of these may be present.	Generally rods and cocci; growth only at usual temperatures
History	Spoilage usually confined to certain portions of pack  In acid products, diagnosis may be less clearly defined; similar organisms may be involved in understerilization and leakage.	Spoilage scattered

^aLeakage may be due not to can defects but to other factors, such as contamination of cooling water or rough handling, e.g., can unscramblers, rough conveyor system.

Table 5-11. pH range of a few selected commercially canned foods.

Food	pH range	Food	pH range
Apples, juice	3.3-3.5	Pears (Bartlett)	3.8-4.6
Apples, whole	3.4-3.5	Peas	5.6-6.5
Asparagus, green	5.0-5.8	Pickles, dill	2.6-3.8
Beans, baked	4.8-5.5	Pickles, sour	3.0-3.5
Beans, green	4.9-5.5	Pickles, sweet	2.5-3.0
Beans, lima	5.4-6.3	Pimento	4.3-4.9
Beans, soy	6.0-6.6	Pineapple, crushed	3.2-4.0
Beans with pork	5.1-5.8	Pineapple, juice	3.4-3.7
Beef, corned, hash	5.5-6.0	Pineapple, sliced	3.5-4.1
Beets, whole	4.9-5.8	Plums	2.8-3.0
Blackberries	3.0-4.2	Potato salad	3.9-4.6
Blueberries	3.0-3.6	Potatoes, mashed	5.10
Boysenberries	3.0-3.3	Potatoes, white, whole	5.4-5.9
Bread, white	5.0-6.0	Prune juice	3.7-4.3
Bread, date and nut	5.1-5.6	Pumpkin	5.2-5.5
Broccoli	5.2-6.0	Raspberries	2.9-3.7
Carrot juice	5.2-5.8	Rhubarb	2.9-3.3
Carrots, chopped	5.3-5.6	Salmon	6.1-6.5
Cheese, Parmesan	5.2-5.3	Sardines	5.7-6.6
Cheese, Roquefort	4.7-4.8	Sauerkraut	3.1-3.7
Cherry juice	3.4-3.6	Sauerkraut juice	3.3-3.4
Chicken	6.2-6.4	Shrimp	6.8-7.0
Chicken with noodles	6.2-6.7	Soup, bean	5.7-5.8
Chop suey	5.4-5.6	Soup, beef broth	6.0-6.2
Cider	2.9-3.3	Soup, chicken noodle	5.5-6.5
Clams	5.9-7.1	Soup, clam chowder	5.6-5.9
Cod fish	6.0-6.1	Soup, duck	5.0-5.7
Corn, cream style	5.9-6.5	Soup, mushroom	6.3-6.7
Corn, on-the-cob	6.1-6.8	Soup, noodle	5.6-5.8
Corn, whole grain, brine-packed	6.0-6.4	Soups, oyster	6.5-6.9
Corn, whole grain, vacuum-packed	6.0-6.4	Soups, pea	5.7-6.2
Crab apples, sliced	3.3-3.7	Soups, Spinach	4.8-5.8
Cranberry juice	2.5-2.7	Soups, Squash	5.0-5.8
Cranberry sauce	2.30	Soups, Tomato	4.2-5.2
Currant juice	3.00	Soups, Turtle	5.2-5.3
Dates	6.2-6.4	Soups, vegetable	4.7-5.6
Duck	6.0-6.1	Strawberries	3.0-3.9
Figs	4.9-5.0	Sweet potatoes	5.3-5.6
Frankfurters	6.2-6.2	Tomato juice	3.9-4.4
Fruit cocktail	3.6-4.0	Tomatoes	4.1-4.4
Gooseberries	2.8-3.1	Tuna	5.9-6.1
Grapefruit, juice	2.9-3.4	Turnip greens	5.4-5.6
Grapefruit, pulp	3.40	Vegetable juice	3.9-4.3
Grapefruit, sections	3.0-3.5	Vegetables, mixed	5.4-5.6
Grapes	3.5-4.5	Vinegar	2.4-3.4
Ham, spiced	6.0-6.3	Youngberries	3.2-3.7
Hominy, lye	6.9-7.9	Miscellaneous products
Huckleberries	2.8-2.9	Beers	4.0-5.0
Jam, fruit	3.5-4.0	Ginger ale	2.0-4.0
Jellies, fruit	3.0-3.5	Human blood plasma	7.3-7.5
Lemon juice	2.2-2.6	Duodenal contents	4.8-8.2
Lemons	2.2-2.4	Feces	4.6-8.4
Lime juice	2.2-2.4	Gastric contents	1.0-3.0
Loganberries	2.7-3.5	Milk	6.6-7.6
Mackerel	5.9-6.2	Saliva	6.0-7.6
Milk, cow, whole	6.4-6.8	Spinal fluid	7.3-7.5
Milk, evaporated	5.9-6.3	Urine	4.8-8.4
Molasses	5.0-5.4	Magnesia, milk of	10.0-10.5
Mushroom	6.0-6.5	Water
Olives, ripe	5.9-7.3	Distilled, CO2	6.8-7.0
Orange juice	3.0-4.0	Mineral	6.2-9.4
Oysters	6.3-6.7	Sea	8.0-8.4
Peaches	3.4-4.2	Wine	2.3-3.8

Contents

Headspace Gas Determination by Gas-Liquid Chromatography (Landry et al., 1988)

Nitrogen, the principal gas normally present in canned foods during storage, is associated with lesser quantities of carbon dioxide and hydrogen. Oxygen included in the container at the time of closure is initially dissipated by container corrosion and/or product oxidation. Departure from this normal pattern can serve as an important indication of changes within the container, since the composition of headspace gases may distinguish whether bacterial spoilage, container corrosion, or product deterioration is the cause of swollen cans (Vosti et al., 1961). Use of the gas chromatograph for analyzing headspace gases of abnormal canned foods has eliminated the possibility of false-negative tests for different gases. It has also allowed the analyst to determine the percentage of each gas present, no matter what the mixture is. By knowing these percentages, the analyst can be alerted to possible can deterioration problems or bacterial spoilage. A rapid gas-liquid chromatographic procedure is presented here for the determination of carbon dioxide, hydrogen, oxygen, nitrogen, and hydrogen sulfide from the headspace of abnormal canned foods.

The analysis of 2,352 abnormal canned foods, composed of 288 different products by a gas-liquid chromatography showed viable microorganisms in 256 cans (Landry et al., 1988). Analysis of this data showed that greater than 10% carbon dioxide in the headspace gas was indicative of microbial growth. Although greater than 10 % carbon dioxide is found in a container, long periods of storage at normal temperatures can result in autosterilization and absence of viable microorganisms. Carbon dioxide my be produced in sufficient quantities to swell the container. Storage at elevated temperatures accelerates this action. Hydrogen can be produced in cans when the food contents react chemically with the metal of the seam (Landry et al., 1988).

 
1. Equipment and materials

1. Fisher Model 1200 Gas Partitioner, with dual thermal conductivity cells and dual in-line columns. Column No. 1 is 6-1/2 feet (1.98 m) ´ 1/8 inch (3.18 mm), aluminum packed, with 80-100 mesh ColumpakTM PQ. Column No. 2 is 11 feet (3.35 m) ´ 3/16 inch (4.76 mm), aluminum packed, with 60-80 mesh molecular sieve 13X ( Figure 5-1 ).

NOTE: Other gas chromatograph instruments equipped with the appropriate columns, carrier gas, detector and recorder or integrator may also be suitable for this analysis.

Operating conditions : column temperature, 75ºC (167ºF); attenuation, 64/256; carrier gas, argon, with in-let pressure of 40 psig; flow rate, 26 ml/min through gas partitioner and 5 ml/min through flush line; bridge current, 125 mA; column mode, 1 & 2; temperature mode, column; injector temperature, off.

NOTE: Installation of flush system. Injection of gas samples through either sample out port or septum injection port may lead to damaged filaments in detector and excessive accumulation of moisture on columns due to bypassing the sample drying tube. To avoid this, make all injections in the sample in port. To avoid cross-contamination, install a flush line off the main argon line ( Figure 5-2 ), and flush sample loop between injections.

2. Strip chart recorder, with full scale deflection and speed set at 1 cm/min, 1 mv.
3. Can puncturing press ( Figure 5-3 )
4. Sterile stainless steel gas piercers ( Figure 5-4 )
5. Miniature inert valve, with 3-way stopcock and female luer on left side (Popper Sons, Inc., 300 Denton Ave., New Hyde Park, NY 11040), or equivalent ( Figure 5-5 ) .
6. Plastic disposable 10-50 ml syringes, with restraining attachment for maximum volume control ( Figure 5-6 ). Syringes may be reused.
7. Gas chromatograph and caps, for capping syringes (Alltech Associates, Inc., 202 Campus Drive, Arlington Heights, IL 60004), or equivalent ( Figure 5-6 )
8. Beaker, 1 liter, glass or metal
9. Plastic gas tubing, 3 feet (0.91 m) ´ 1/8 inch (3.18 mm) id, for exhaust tubing
10. Soap solution, for detecting gas leaks ("SNOOP" Nuclear Products Co., 15635 Saranac Road, Cleveland, OH 44110), or equivalent
11. Small pinch clamp, to weigh down exhaust tubing in beaker
12. Nupro Valve, flow-regulating valve for flush line, 1/8 inch (3.18 mm), Angle Pattern Brass (Alltech), or equivalent ( Figure 5-2)
13. Silicone rubber tubing, seamless, red, autoclavable, 1/8 inch (3.18 mm) bore ´ 3/16 inch (4.76 mm) wall thickness (Arthur H. Thomas Co., Vine St. at 3rd, Philadelphia, PA), or equivalent.

2. Calibration of gas chromatograph

Calibration gases of known proportions are commercially available. Construct calibration curves from analysis of pure gases and at least 2-3 different percentage mixtures of gases. Plot linear graph of various known concentrations of each gas as peak height (mm) vs. % gas ( Figure 5-7 ).

3. Preparation of materials

Prepare gas collection apparatus as illustrated in Figures 5-8 and 5-9 . Adjust height of gas collection apparatus to height of can to be examined. Attach male terminal of miniature valve to female Luer-Lok terminal mounted on top of brass block on can-puncturing press. Attach one end of gas exhaust tubing to female terminal of miniature valve. Attach small pinch clamp to other end of gas exhaust tubing and place in beaker partially filled with water. Attach disposable syringe to other female Luer-Lok terminal on miniature valve. Turn 2-way plug so that gas entering from piercer will flow toward disposable syringe. Place sterile gas piercer in position on male terminal mounted on bottom of brass block on can-puncturing press.

4. Collection of headspace gas

Place can under gas press (cans to be cultured should first be cleaned and sterilized). Lower handle until gas piercer punctures can and seals. Hold in position until adequate volume of gas has been collected (minimum of 5 ml); then turn 2-way plug to release excess gas through exhaust tubing. Release handle, remove syringe, and cap immediately. Identify syringe appropriately.

5. Injection of gas into gas chromatograph

Turn on gas chromatograph and recorder. Let stabilize for about 2 h. Make sure flush line is attached and gas sampling valve is open to allow flushing of sample loop. Turn on chart drive on recorder. Remove flush line, uncap, and immediately attach syringe to Sample-In Injection Port. Inject 5-10 ml of gas and immediately close gas sampling valve. Remove syringe and cap. Reattach flush line onto Sample-In Port and open gas sample valve to allow flushing of system before next injection. Observe chromatogram and switch attenuation from 64 to 256 after carbon dioxide peak has been recorded and returned back to base line. This allows hydrogen peak to be retained on scale. After hydrogen peak returns to base line, switch attenuation back to 64. After instrument has separated gases (about 6 min), determine retention time and peak height for each gas recovered from unknown sample and % determined from standard graph by comparing retention times and peak heights with known gases, usually associated with headspace gases from abnormal canned food products. Mount chromatogram on mounting paper and identify properly as in Figure 5-10 . For each sample examined, inject control gases for each type of headspace gas recovered.

Contents

Modification of Headspace Gas Analysis Methodology, Using the SP4270 Integrator (Landry and Margarito, 1998)

This section may be used as an alternative method by laboratories that have the necessary equipment and expertise.

The use of the SP4270 Integrator in place of the strip chart recorder will free the analyst from time-consuming calculations and identification procedures because the analyst need not monitor the instrument constantly to change the attenuation and stop the procedure between injections. With the integrator, the analyst can simply enter a few basic instructions and a little pertinent information before injections and the integrator will print a report with the analyst's name or initials, sample number, sub number, chromatogram, and the gases detected with their %.

1. Equipment
1. Fisher gas partitioner Model 1200, with dual thermal conductivity cells and dual in-line columns. Column No. 1 is 6-1/2 feet (1.98 m) ´ 1/8 inch (3.18 mm), aluminum packed, with 80-100 mesh Columpak PQ™. Column No. 2 is 11 feet (3.35 m) ´ 3/16 inch (4.76 mm) aluminum packed with 60-80 mesh molecular sieve 13X ( Figure 5-11 ).

NOTE: Other gas chromatograph instruments equipped with the appropriate columns, carrier gas, detector and recorder or integrator may also be suitable for this analysis.

Operating conditions  Column temperature = 75ºC (167ºF)  Attenuation = 64  Carrier gas = Argon, with inlet pressure of 60 psig  Flow rate = 41 ml/min through gas partitioner, 5 ml/min through flush line  Bridge Current = 125 mA  Column mode = 1 & 2  Temperature mode = Column  Injector temperature = Off

2. Standby power system, Model SPS 200-117, SAFT America Inc., Electronic Systems Division, 2414 W. 14th St., Tempe, AZ 85281 ( Figure 5-12 ).
3. Spectra-physics integrator, Model SP4270, Spectra-Physics, Autolab Division, 3333 N. First St., San Jose, CA 95134 ( Figure 5-13).

2. Integrator programming

After turning system on and entering date and time, enter dialog portion of system and program all information as listed in .

3. Procedure for calibration injections
With gas partitioner on and integrator connected in the same fashion as strip chart recorder had been previously, make calibration injections with concentrations listed, where:
 VA(l)/VN(1) = % composite
 VA(2)/VN(2) = % CO₂
 VA(3)/VN(3) = % H₂
 VA(4)/VN(4) = % 0₂
 VA(5)/VN(5) = % N₂
• Detach flush line from Sample-In Port.
• Attach calibration gas onto Sample-In Port and inject 10 ml.
• Immediately push in plunger to inject gas and push INJ A button on integrator.
• Remove calibration gas and attach flush line.
• Pull out plunger to flush sample loop.
• After integrator has computed calibration (approximately 4 min) repeat these steps until all 14 calibrations have been performed.
At the end of these calibration injections the integrator will compute and print the coefficients of least squares fit to a quadratic equation. The calibration procedure of the instrument has now been completed and is ready for use.

By following the instructions ( Figure 5-15), the analyst can enter his initials, the control gases to be used in conjunction with the sample, the sample No. (omitting the year prefix), and the subsample No. This will program the integrator to print the information so that the final printout is identified and ready for submission with the sample report.

Figure 5-16 is an example of a final printout.

4. Discussion

Past experience has shown that the system, although fairly linear, is not linear enough. When the integrator is programmed to use a nonlinear program, it uses quadratic equations to determine nonlinear curves.

A series of standard concentrations was used to achieve a low, middle, and high concentration of each particular gas for greater accuracy. Fewer calibrations could possibly be carried out, but a loss of accuracy might result.

The analyst should be aware that the SP4270 uses a 3-function keypad. The lower section of each key initiates a system function, while the upper portion represents numeric/punctuation characters (upper left) and alpha characters (upper right) (see Figures 5-13 and 5-17 ).

The SHIFT key is used to shift the keypad from one key section to the other. The EDIT lights -- located on the right-hand side of the keypad -- indicate which key section is currently being accessed for which channel.

This is important for entering information such as CO₂ which is a mixture of numeric and alpha characters, or the sample number, where the integrator is programmed to accept alpha characters but the numeric characters must be entered.

5. Operating conditions for integrator (Figure 5-18).

Contents

Examination of metal containers for integrity (Lin et al., 1998)

The quality of a food container is determined by its ability to protect the product it contains from chemical deterioration or microbiological spoilage. Good double and side seams are essential to a good hermetic seal, particularly at the cross-over (juncture); however, the performance of a can is also affected by many other factors. Spoilage within the can may be caused by leakage, underprocessing, or elevated storage temperatures. Leaker spoilage occurs mainly from seam defects and mechanical damage. Improper pressure control during retorting and cooling operations may stress the seam, resulting in poor seam integrity and subsequent leaker spoilage. However, the rate of container defects that might result in food spoilage is usually low.

The suitability of the particular food to be preserved also affects the performance of the container. Hydrogen swells and sulfide stains caused by chemical corrosion sometimes occur. In addition, prolonged storage of cans at elevated temperatures promotes corrosion and may result in perforation. Improper retorting operations, such as rapid pressure changes, may cause can deformation and damage seam integrity. Post-process contamination by nonchlorinated cooling water or excessive buildup of bacteria in can-handling equipment may also cause spoilage, and abusive handling of containers may result in leaker spoilage.

Although the incidence of spoilage in canned foods is low, it is necessary to know how to proceed with the investigation of the integrity of the can when spoilage does occur. This chapter presents methods for seam examination and leakage detection.

Container examinations associated with food spoilage are usually accompanied by pH determination of the product, gas analysis of can headspace, and microbiological testing of the product. Analytical results that depart from normal patterns may indicate changes within the container and help to pinpoint the cause of spoilage.

The double seam ( Figure 5-19) consists of 5 thicknesses of plate (7 thicknesses at the juncture of end and side seam for 3-piece soldered cans, and 6.3-6.4 thicknesses at the juncture for welded cans) interlocked or folded and pressed firmly together, plus a thin layer of sealing compound. It is formed in 2 rolling operations. The side seam is bonded by welding or with solder or adhesive cement. Side seams of soldered cans consist of 4 thicknesses of metal body plate, except at the laps or cross-over areas, which have 2 thicknesses of metal. Side seams of welded and cemented cans have 2, or parts of 2, thicknesses of metal body plate (1.3-1.4 times the metal plate thickness for welded cans).

[NOTE: the use of lead solder to close the seams of food cans is rapidly being prohibited in many nations.] Welded 3-piece cans permit reduction of side seam thickness and double seam thickness at the cross-over. Drawn cans eliminate the side seam and bottom end seam, resulting in fewer areas that affect can integrity. Can ends ( Figure 5-20) are punched from sheets; edges of the ends are curled, and a sealing compound is applied and dried in the lining channel (curl and flat areas) of the can end. Once the lined can end is double seamed onto a can body, the sealing compound in this compressive seal fills the voids (spaces) between the folds of metal in the properly made double seam to form an abuse-resistant hermetic seal.

1. Sampling and sample size

Sample size required for product analysis and can examination depends on the type of spoilage and complexity of the problem. When the cause of spoilage is clear, 4-6 cans may be enough. In more complex cases, it may be necessary to examine 50 or more cans. An adequate number of normal (flat) cans should be taken from the same case or lot for examination.

2. Preliminary examination

Remove labels, assign subnumbers, if necessary, and separate code numbers. Use same coding or subnumber system for both product and container examinations. Before removing any product sample, perform complete external can examination, observing such defects as evidence of leakage, pinholes or rusting, dents, buckling, and general exterior conditions.

Classify each can as (a) flat, (b) flipper, (c) springer, (d) soft swell, or (e) hard swell according to criteria in "Examination of Canned Food, Table 5-1." Leakage tests and external double seam dimensions may not be valid when cans are buckled. However, these cans should be examined and then torn down and re-examined for seam defects that may have existed before buckling. If possible, set aside reserve cans representing the classifications noted. Refrigerate reserve cans to prevent bursting.

Examine cans classified as springers and soft and hard swells immediately.Do not incubate. Remove sample from uncoded end of can in a manner that will not disturb double seam, e.g., with bacteriological can opener (Figure 5-21). If can end has been punctured as a result of gas sampling, bacteriological can opener may be used if puncture is in center of end. If puncture is not in center, remove end with a pair of metal cutters.

3. Can examination

Note condition of cans (exterior and interior) and quality of seams. Observe and feel for gross abnormalities, mechanical defects, perforations, rust spots, and dents. Perform pressure and/or vacuum tests to detect invisible microleaks either in double seams or side seams. Measure seam dimensions and perform teardown examination. Note condition of double seam formation and construction (by micrometer, seam scope, or seam projector). Chemical, instrumental, metallographic, and other techniques may be required.

1. Visual examination

Use hand as well as eye. A magnifying glass with proper illumination is helpful. Run thumb and forefinger around seam on inside (chuck wall) and outside of seam to locate any roughness, uneveness, or sharpness. Examine by sight and touch for the following defects that may result in can leakage (for definition of terms, see glossary at end of this chapter):

 
• sharp seam
• code cut
• cutovers or cut-throughs
• false seam (although some false seams may not be detected by external examination)
• dents
• deadheads (incomplete seam)
• excessive droop
• jumpover
• excessive scuffing in chuck wall area
• knocked-down flange
• excess solder
• cable cuts on double seam
2. Microleak detection

The microleak tests are not listed in their order of sensitivity, nor is it necessary to use them all. Each has its advantages and disadvantages, depending on the particular set of conditions. In some instances a test may be chosen as a personal preference. They are all presented to provide the analyst with all the procedures and available options. Make all external measurements of can double seams before any microleak testing. See section on double seam measurements.

1. National Food Processors Association (NFPA, formerly National Canners Association) Vacuum Leak Test (Bee et al., 1972)(Figure 5-22).

This test applies a vacuum to the can, which more closely duplicates the condition in the can when it contains product and is sealed. Proponents of this method feel that using a vacuum to detect leakage in a can designed to hold a vacuum is more effective than using pressure. The use of a vacuum may remove food particles from leakage paths in can seams; pressure may force particles more deeply into leakage paths.

1. Materials
• Bacteriological can opener(Figure 5-21) (Wilkens-Anderson Co., 4515 W. Division St., Chicago, IL 60651) or equivalent
• Plexiglas plate
• Plastic tubing
• Rubber gasket, to fit container being examined
• Vacuum source with gauge
• Nonfoaming wetting agent, e.g., Triton X-100 (R86)
• Outside light source, such as high-intensity lamp
2. Procedure

Remove uncoded end of can with bacteriological can opener adjusted to cut out can end, leaving ¼ inch (0.6 cm) border around outer edge. Empty and wash container with water and suitable detergent to remove food particles lodged in seam area. (Ultrasonic cleaner may be used to remove small food particles lodged in seam areas.) Add wetting agent plus water to depth of about 1 inch (2.5 cm). Place Plexiglas plate with tubing attached and wetted rubber gasket on open end of container. Increase vacuum until gauge indicates vacuum of 15-25 inches (381-635 mm). Swirl water in container to dissipate small bubbles produced by application of vacuum. Tilt container slowly to immerse all seam surfaces, letting light source focus through Plexiglas into can for better observation. Rotate tilted can so that all surfaces are observed and covered with water. Depending on size of hole, path of leakage, pressure differential, and surface tension of the test water, bubbles will appear smaller or larger and with lesser or greater frequency. Release vacuum by first closing main vacuum petcock and then opening intake petcock.

2. Mead jar test (ACC, 1975)(Figure 5-23)

This nondestructive examination determines leakage paths of finished cans that have both ends double seamed. It is used primarily for vacuum- or nonvacuum-packed dried or semidried products. Deaerated water is preferred because, as vacuum is pulled on the jar, dissolved air in the water comes out of solution as bubbles, preventing a clear view of the container and any leakage bubbles. This test would rarely be used for items thermally processed in metal cans.

1. Materials
• Mead jar (battery jar), glass or plastic
• Mesh protector, to fit around Mead jar
• Metal top with rubber gasket on bottom side and air inlet, vacuum inlet, and vacuum gauge on top side
• Vacuum source
• Rubber tubing
• Deaerated water (prepare by applying 25-30 inches of vacuum on water for 8 h (635-762 mm) or overnight)
• Vaseline or stopcock grease
• Device or weight to hold can under water

2. Procedure

Place enough deaerated water into Mead jar to completely submerge test container. Put container in water and, if necessary, place device or weight on it to hold it under water. Place mesh protector around jar, and put Vaseline on rubber gasket on underside of top piece to act as sealant between gasket and lip of Mead jar. Place lid on top of jar and rotate it to improve seal. Attach rubber hose to vacuum line. Turn off air inlet stopcock and open vacuum line stopcock. Turn on vacuum and record vacuum reading on gauge if leakage or air bubbles emanate from container. Note location of leakage point. Turn up to full vacuum if no leakage is noted. Turn off vacuum and open air inlet valve to release vacuum. Take off lid, remove container, and mark leakage point.

CAUTION: Do not use defective or cracked Mead jars because of danger of collapsing them. Always put wire mesh protector in place before turning on vacuum. For a container to be classified as a leaker, a continuous stream of bubbles from a single point is necessary. Unless leakage is obvious, the can should be observed under test conditions for at least 30 s. Generally, a few bubbles will be seen when the vacuum is first applied because of air entrapment in the double seams. These should not be confused with leakage point bubbles.

3. Air pressure test (ACC, 1975) (Figure 5-24)

For detection of container leakage caused by minute body pinholes and perforations, and/or defective side seams, air pressure testing is the most convenient and conclusive. It is also helpful for locating double seam leaks. During pressure testing, double seams may be distorted, producing false leakers or sealing off minute leakage paths. For this reason, the air pressure testing method should be used in conjunction with the fluorescein test or penetrant dye test to trace the actual leakage path through double seams.

1. Materials
• Single pocket (or multiple pocket) foot tester with attached air and water source
• Manually operated air pressure control valve and pressure gauge installed on air line
• Two gate valves installed in air line, one to pressurize and the other to exhaust the can during testing

2. Procedure

Preparation of samples. Open filled cans at one end with bacteriological can opener so that double seam remains intact. Manufacturer's end is usually opened, but if enough samples are available, half the cans may be opened at packer's end. After removing contents, wash cans thoroughly. Wash containers of fatty or oily products with warm detergent and water, or boil them in detergent and water; use ultrasonic cleaner to remove all fat or oil trapped in the double seam. Dry cans at least 8 h at 100-120ºF (37.7-48.9ºC) before pressure testing.

Pressure test. Fill foot tester with warm water (100-120ºF; 37.7-48.9ºC) to about 2 inches (5.1 cm) from top. Set air pressure control valve at desired pressure level (20 pounds [9.1 kg] for most sanitary cans). Seat open end of test can against rubber base plate, side seam up, and lower pressure bar against can with just enough pressure to hold can in place. Secure pressure bar in this position with 2 nuts so that adjustment is not necessary for testing additional cans of same size. Close exhaust gate valve and completely immerse can in tank by stepping on foot pedal. With can completely immersed, open pressurized gate valve, letting air flow into can. Hold can in this position long enough to detect any leakage points.

Leakage may be shown by steady stream of large bubbles or continued intermittent escape of very tiny bubbles. If leakage is present, close pressurized gate valve and exhaust can by opening exhaust gate valve. Release foot pressure and lift can out of water. Rotate can 180º against rubber base plate until new area of can is exposed, and repeat pressure testing operation. Mark location of any leaks noted during test for use as reference when cans are examined further. Do not exceed 30 psi (207 kPa) because can may burst beyond this level.

After pressure testing, use fluorescein test to obtain additional information on presence of any leakage paths, or strip can seams for further examination if point of leakage is conclusively located.

3. General comments

During pressure testing operation, pay particular attention to cross-over areas and double seams on both ends of can. Also observe side seam area closely and scan bodies for pinholes or perforations. Use warm water during test. During drying, small leakage paths will be opened; these may be reclosed by contraction of the can during testing in cold water.(NOTE: The air pressure test must not be rushed. Very small leaks may take several s to show up, and then the only evidence may be the intermittent flow of very tiny bubbles.)

4. Fluorescein dye test (ACC, 1975)

Fluorescein dye testing has been used for many years to detect minute double seam, lap, and side seam leakage paths in all types of containers. The fluorescein test is especially useful for examining sanitary-style containers that are normally packed with some initial vacuum. Fluorescein dye can often be used to detect minute leakage paths on suspected cans that do not leak under the air pressure test. Fluorescein testing of most types of containers under vacuum simulates actual packed condition, i.e., with ends pulled inward.

1. Materials
• Vacuum line, with bleed-valve attachment for regulating amount of vacuum to be used
• Rubber-faced plate, for attaching containers to vacuum line
• Ultraviolet (UV) light (Black Light Lamp, Figure 5-25)
• Fluorescein dye solution. Mix 100 ml triethylene glycol, 300 ml water, 15 g glycerine, 3 g wetting agent, such as Triton X-100 (R86), and 3 g sodium fluorescein, technical grade. (Zyglo dye solution ZL-4B is available from Magnaflux Corporation, Chicago, IL.)

2. Procedure

Preparation of sample. Open filled cans at one end with bacteriological can opener so that double seam remains intact. Manufacturer's end is usually opened, but if enough samples are available, half the containers may be opened at packer's end. After removing contents, wash and dry containers thoroughly. Wash containers of fatty or oily products with hot detergent and water, or boil them in detergent and water to remove all fat or oil trapped in double seams. Use ultrasonic bath to remove small food particles lodged in seam areas.

Vacuum application( Figure 5-26). Place opened end of emptied and dried container against vertically mounted rubber-faced plate connected to vacuum line. As a general rule, 15-20 inches (381-508 mm) of vacuum is used for most pressure-processed sanitary-style containers. For other container styles, maximum allowable vacuum to be used depends on panel resistance of bodies.

After container is mounted in place and vacuum drawn, apply fluorescein solution with a small brush or eyedropper to outside double seam and side seam areas.OR place can in dye bath to cover seam and/or score areas to be examined. Run test for 30 min to 2 h, depending on style of container being examined. Longer test period may be required to detect microleaks. If in doubt as to time needed to demonstrate leakage, remove containers every 30 min and check inside with UV light for presence of fluorescein. Since fluorescein solution runs off the mounted container, apply fresh solution at 15 min intervals.

Container examination. At end of vacuum test period, thoroughly remove fluorescein remaining on outside of containers with water; then wipe dry. Take special care not to splash any fluorescein into opened end of container. After cleaning excess solution from outside, strip the double seam and examine it under UV light to detect any fluorescein on the inside. Do not allow wet solution trapped in outside of double seam to creep inside container, thus giving false-positive results. Also, keep tools clean of fluorescein to prevent contamination during stripping. Examine containers immediately after vacuum testing, since dried fluorescein solution does not fluoresce( Figure 5-26).

5. Double seam measurement (ACC, 1975; ACC, 1978)

NOTE: See sample report forms for double seam examination( Figure 5-27) and for the complete container integrity examination( Figure 5-28).

 
1. Measure seam width (length, height), thickness, and countersink on both can ends before can is opened, if possible. Seam width and thickness may be measured after opening if bacteriological can opener is used. However, take care to prevent distortion of area around seaming panel. Countersink cannot be measured after end is removed. Perform teardown examination and record results for seam integrity evaluation. Use seam scope, projector technique, or micrometer measurement (or all 3 systems) for verification, to determine adequacy of double seam formation.
2. Teardown and cross-section strip examinations
1. Materials (stripping tools, Figure 5-29)
2. Procedure.NOTE: The seam projector examination is easier to perform before the cover hook is removed and after the seam has been cut. If uncoded end is still on can, remove with bacteriological can opener. Empty contents from can. Wash, dry, and test can for leakage, as previously described. After leakage test, cut 2 strips about 3/8 inch (1 cm) wide through double seam and into body of can about 1-1/4 inches (3.2 cm), leaving bottom of strips attached to can. One strip should be at least 1/2 inch (1.3 cm) counterclockwise from juncture; the other should be 180º from lap or side seam. This will leave an adequate length of cover hook for thorough examination. Remove remaining end metal, beginning at cutout strip closest to side seam, moving clockwise until entire cover hook is removed( Figures 5-30 and 5-31). If rocker-like motion does not work, pull out and away (Figure 5-31). Take care to prevent any injury or cut. Partially remove coded end with bacteriological can opener, leaving it attached about 90º counterclockwise from side seam so that the can may be identified after stripping. Then cut strips into coded end of can and tear it down, using procedures previously described.

Strip off cover hook to point where remaining end metal has not been removed (about 1/2 inch (1.3 cm) from second metal strip). Measure body and cover hooks. Grade cover hook for tightness by examining and evaluating wrinkles. Examine cross-over area of 3-piece soldered cans for wrinkles and for crawled laps (body hook of one side of cross-over drops down or crawls below bottom of other side) in soldered cans.

Observe double seams for plate fractures. Inspect interior of body wall in double seam area for well-defined continuous impression around circumference of can. This is referred to as pressure ridge and is one indication of seam tightness, although pressure ridge may or may not be present in a good seam. Tape cover hooks and coded end to can so that they may be identified as belonging to the can in question. If cover hooks are still attached, bend them inward inside the can body to prevent cut injury.

3. General comment

As mentioned previously, measure countersinks while ends of can are still intact. On swelled cans these measurement are seldom meaningful because of possible distention caused by swelling. However, measurements that indicate deep countersinks are useful because they represent the condition as is.

6. Side seam examination

NOTE: Food products are packed in 2 basic types of cans: the 2- and 3-piece cans. The 2-piece can has a drawn body, no side seam, and only one double seamed end, thus the term 2-piece. Side seam and lap examination are not applicable to these cans. Three-piece can bodies are made from a flat plate, which is rounded and seamed to form a cylinder. These cans have 2 double seam ends, thus the term 3-piece. The side seam is sealed by solder, adhesive, or welding, and is in addition to the double seam, which is susceptible to leakage.
 

1. Soldered side seam examination
1. Materials (stripping tools and side seam breaker)
2. Procedure

Break open and observe both laps. Note solder voids and channels, and discolored and stained solder. Identify hot and cold breaks in solder. Observe flange area of the lap closely for defects. Examine side seam construction, pulling apart older bond with side seam breaker( Figure 5-32) as follows. Place can over body horse of appropriate can diameter and pull down on breaker arm to expand can and open solder bond. Observe side seam for solder voids, channels, and discolored areas.

Examine laps for heavy solder, evidenced by excessive solder adjacent to lap inside and outside can, or on body hook, causing severely crawled lap or cutover. Break open lap to see if excessive solder is still present in lap.

3. General comments

The portion of the cover hook that intersects the side seam is called the juncture area and is about 3/8 inch (1 cm) wide. In an ideally made 3-piece can, length of cover hook is not reduced at the juncture, even though cover hook is depressed at this point. In most commercial 3-piece cans, length of the cover hook is reduced at the side seam in varying degrees. The shortening of the cover hook at the side seam is caused by the 2 additional thicknesses of body flange at the side seam. These additional layers of metal prevent the cover hook from being tucked up under the body hook as it is under the body hook away from the side seam.

A good juncture with sufficiently long cover and body hooks is essential. Without a good juncture, the overlap at the side seam may be critically short, making the can less abuse-resistant. As with the tightness rating, which is based on the wrinkle-free metal of the hook length, the juncture rating is based on the amount of droop-free metal for the existing hook length away from the juncture. Because the cover hook is frequently shorter at the juncture in the form of a droop, the juncture is rated on a percentage scale, starting at 100% (ideal) and decreasing in 25% increments. If the cover hook in the juncture is even with the rest of the cover hook, it is rated 100%. If the cover hook reduction at the juncture is about 1/4 the length of the cover hook, the juncture is rated 75%. If the cover hook at the juncture is 1/2 the length of the rest of the cover hook, the juncture is rated 50%. Similarly, if the cover hook length at the juncture is only ¼ the length of the rest of the cover hook, it is rated 25%.

A severe condition of crawled laps results in an area of little overlap at the cross-over, creating a possible leakage point. This condition is usually, but not always, accompanied by an external droop at the cross-over. Cover hooks made with double cold reduced (2 CR) ends may look wrinkled, but these wrinkles may be reverse wrinkles, which do not indicate a loose seam. Compound wrinkles do not give wavy cut edges to the cover hook and are not used to establish tightness ratings. Discolored or stained solder may indicate previous leakage through the lap. It is not necessary to have a solderless channel for leakage to occur at the lap. This can happen as a result of either a hot break or a cold break in the solder. Both of these conditions are conducive to container leakage. A hot break is identified by solder that appears relatively smooth; it occurs in the soldering operation during manufacture when the lap opens up before the solder solidifies completely. A cold break gives the solder a round, mottled appearance; if leakage has occurred at this point, the area shows a dark discoloration. Cold breaks may occur at almost any time after the solder has hardened. They are difficult for manufacturing plants to detect because they usually occur after manufacturing. Cold breaks are usually caused by weak soldering bonds or poor manufacturing techniques.

In general, if pressure testing shows leakage at the cross-over, if the fluorescein test indicates a path through the flange area, and if no other double seam or lap defects are found at the cross-over, the most likely cause of leakage is a solder break at the flange area of the lap. It is also possible to have no solder at this area. This defect is easier to detect visually than the solder break. The leakage path may be confirmed by a fluorescein path or by stained or darkened solder. A condition known as an "island" is often observed in the side seam. An island is an isolated area in the side seam fold that is void of solder, but without a connecting solderless path, or break, leading to the outside of the can. This condition is not necessarily associated with leakage, but does indicate a weak side seam.

2. Welded side seam examination
1. Materials (stripping tools and side seam breaker)
2. Procedure

Examine the flange area for flange cracks, the weld for blow holes or weld splashes, and the lap area for fishtail.NOTE: A fishtail is a piece of metal extending beyond the flange at the lap area that might cause double seam difficulty. Any of the above defects in the weld may result in leakage. However, this should be supported by a valid leak test.

3. Micrometer measuring system [21 CFR 113.60(a)(1)]
1. Materials

Use a micrometer especially made for measuring double seams and reading to nearest 0.001 inch (0.025 mm). Be sure to adjust micrometer properly. When micrometer is set at zero position, zero graduation on movable barrel should match exactly with index line on stationary member. If zero adjustment is more than 1/2 space from index line at this setting, adjust it.

2. Procedure

Make seam measurements on round cans, at minimum of 3 points about 120º apart, around circumference of can, beginning about an inch (2.5 cm) to one side of cross-over (or at least 1/2 inch (1.3 cm) away from cross-over). Obtain the 5 required measurements: seam thickness; seam width (length, height); body hook length; cover hook length; and tightness (observation for wrinkle). The 2 optional measurements are countersink depth and overlap, calculated by the following formula:

Overlap = CH + BH + T - W

where CH is cover hook length, BH is body hook length, T is cover plate thickness, and W is seam width (height, length). Grade tightness (wrinkle) (ACC, 1978) of double seam by examining cover hook wrinkle according to percentages illustrated in Figures 5-33 and 5-34. Drawing shows cover hook with 0-100% tightness, with wrinkle number shown below it. Tightness can also be indicated by flatness of cover hook; that is, cover hook should not appear round. Make this observation on cover hook removed from seam that has been sectioned with seam saw ( Figure 5-35). This method is good verification for wrinkle method but should not be a substitute for it. Tightness may be expressed in terms of percentage of cover hook not included in wrinkle or by rating number equivalent to distance up cover hook. Both procedures are listed below. Percentage method is preferred.

Tightness, expressed in terms of wrinkles:

 No. 0 - Smooth, no wrinkle
 No. 1 - Wrinkle up to 1/3 distance from edge
 No. 2 - Wrinkle up to 1/2 distance from edge
 No. 3 - Wrinkle up to more than 1/2 distance from edge

Tightness ratings expressed in % of cover hook not included in the wrinkle (preferred method):

 100 - Equivalent to No. 0
 90 - Equivalent to between Nos. 0 and 1
 70 - Equivalent to No. 1
 50 - Equivalent to No. 2
 <50 - Equivalent to No. 3
Rate the juncture as previously described. Measure free space to determine seam condition of 2-piece oblong and 2-piece oval cans, as follows: FS = ST - (2BPT + 3CPT) where ST is seam thickness, BPT is body plate thickness, and CPT is cover plate thickness.NOTE: Specifications are not yet well established.
4. Seam projector measuring system [21 CFR 113.60(a)(1)]

As an alternative to the use of the micrometer, or as a verification, cross-sections of double seams may be examined visually with a seam projector. A section of the double seam is cut in the form of a metal strip that remains attached to the can body and that is then placed in the projector. From the image projected on the screen, the seam width, hook lengths, and overlap dimensions may be measured with a specially calibrated caliper. General seam formation and, in some instances, seam tightness may be observed. The seam projector method facilitates examination of the critical overlap area at the cross-over; this is especially valuable for examining 3-piece soldered No. 10 cans, which are particularly vulnerable to leakage at this point.

1. Materials
• Seam projector (Wilkens-Anderson)( Figure 5-35)
• Waco saw (Wilkens-Anderson)( Figure 5-35)
• Micrometer
2. Procedure

Obtain the 4 required measurements: body hook length, overlap, seam thickness, and tightness (observation for wrinkle). The 3 optional measurements are width (length, height), cover hook length, and countersink depth. Measure each double seam characteristic at 2 different locations on each double seam, excluding the cross-over. Cut cross-sections through double seams with Waco seam saw. Polish cross-section surface with fine emery cloth to ensure bright surface that will project clear image on screen. Place polished section in clamp on side of projector, look into shadow box, and observe image. Bring calipers in instrument into position. Note any looseness, tightness, or other malformations. With calibrated calipers, carefully measure and record width, cover hook, body hook, and overlap on image. Repeat this procedure in all 4 different locations along double seam. To properly evaluate seam for degree of looseness, strip cover hook from can, and visually grade for wrinkle formation. Observe absence or discontinuities of sealing compound after cover hook is removed from double seam. Enter observations on Figure 5-28 (shown at end of this chapter). Sealing compound should form complete 360º circle around edge of lid.

Overlap percentage is a measure of both how well end hook and body hook overlap and how well hooks match each other in length. It is also a ratio of the existing distance between body hook and cover hook compared to the distance the hooks would lap for the given seam. Overlap percentage is measured directly when seam projector is used with nomograph placed on viewing screen ( Figure 5-36). Calculate percentage from seam length, body hook, cover hook, and body and end plate thicknesses.

Overlap, % = 100 ´ (BH + CH + EPT - W)/[W - (2EPT + BPT)]

where BH is body hook length, CH is cover hook length, EPT is end plate thickness, W is width (seam height, length), and BPT is body plate thickness. Use minimum value found for each measurement (maximum value for W), to approximate lowest possible overlap percentage. Overlap may also be measured in thousandth inches or millimeters with calibrated calipers, as above.

Open calipers as wide as possible and place nomograph card on screen. Position nomograph card so that image appears on it and reference lines of nomograph are parallel to hook images. Adjust position of nomograph to place zero line on side of body hook radius of image; then move it forward or backward until the 100 line is on inside of end hook radius. Now, move nomograph, keeping reference lines parallel to hooks and allowing no forward or backward motion, until zero line is at end of end hook; read nomograph at end of body hook. This value is percent overlap. Rate the juncture as previously described.

3. Special tests on rectangular and oval cans (William R. Cole, Division of Hazard Analysis Critical Control Point (HACCP) Programs, FDA)

Sardines are packed predominantly in a shallow rectangular (or oblong) 405x301x014 2-piece (drawn) aluminum can, with a scored, pull-tab type lid (known as "quarter-pound" can; Figure 5-37). A larger volume of fish is packed into an oval 607x403x108 2-piece (drawn) aluminum can (known as "pound oval;" Figure 5-38). A 405 tin-plated steel can and a 405 drawn aluminum can, both without the scored pull-tab top, are also used. The longer western sardine (pilchard) is packed in oval and round cans in 1/4 and l-lb units. Examination of imported sardines for container integrity is much like that for round sanitary cans. This section covers areas that are evaluated differently and specific problems inherent in these cans.

A major integrity problem with these cans is the formation of the so-called cover hook "droop," usually at or near one of the 4 corners of the can, with resulting short overlaps at the droop area. An additional factor is the degree of wrinkle at the corners. If this wrinkle is used to rate cover hook tightness, it often indicates a tightness rating below specifications established by most domestic can manufacturers. However, the remainder of the cover hook away from the corners will, at the same time, appear to have an acceptable tightness rating. The following procedures have been developed for the examination of the 405 and 607 drawn aluminum sardine cans.

1. Visual examination

Visual examination of cans is applicable for 405 and 607 drawn aluminum sardine cans. Be alert to such conditions as minute leakage of packing medium around scored area of lid, as well as base or attachment point of pull tab, on the 405 can. The primary gross closure defect associated with 405 containers has been cover hook droop, usually at or near one of the 4 corners. One cause of droop is product overhanging the can flange before seaming. Visually examine the area surrounding the droop for evidence of product trapped in the seam.

2. Microleak detection

National Food Processors Association (NFPA) Vacuum Leak Test (Bee et al., 1972). Can examination (microleak detection, NFPA vacuum leak test), above, is also applicable for 405 and 607 sardine cans.

 Fluorescein dye test. Use bacteriological cutter to remove portion of no-lid end. Check lids, score, and rivet area for evidence of leakage.

3. Double seam measurements
1. General comments

405x301x014 (quarter-pound) oblong can. The location for micrometer and/or seam projector measurement (i.e., standard for the round sanitary can) may be sufficient to adequately interpret the integrity of the 405 drawn aluminum sardine can. Figure 5-37 illustrates the template that was constructed as a guide for double seam examination of the 405 can. Four points, P₁ to P₄, were selected as locations for seam (projector and/or micrometer) measurements. The P₂ location is stripped and examined for wrinkle and presence of pressure ridge. Length, thickness, body hook, and cover hook are generally measured at P₃ location, and the data are recorded. With respect to examination for wrinkle and pressure ridge, firms that made seam scope measurements would either strip sections of the cover hook from between the measurement points or completely strip another can pulled along with the first.

607x403x108 (l-lb) oval can. Figure 5-38 illustrates template constructed as industry guide for double seam examination of the 607 can. Four points, P₁ to P₄, were selected as locations for seam micrometer and/or seam projector measurements. As with Figure 5-37, P₂ represents cover hook and body wall sections that are to be stripped and examined for tightness and presence of pressure ridge.

2. Data sheet for double seam examination of aluminum sardine cans (607x403x108 and 405x301x014)

As specific points on both the 405 and 607 containers were indicated as potential problem areas, with respect to droop, overlap, and tightness, the 5 recommended points for measurement may be entered under the last column of Figure 5-27 to allow for easier identification of these points. However, the selection of the P₁ location on both cans was designed to provide a general reference point (the 301 side closest to the pull-tab on the 405 can; the point on the 607 can closest to the embossed code) similar to the side seam on a 3-piece container. P₃ and its 3 corresponding points along the straight section of the double seam on the 405 can generally reflect the measurement points used by industry. P₂ and 3 other corner points and adjacent areas have indicated potential weakness with respect to droop, low overlap, and low tightness. Therefore, the data sheet shown in Figure 5-28 allows immediate comparison of data obtained on 2 sets of points. If the visual and microleak examinations indicate one particular weak area of the seam, double seam teardown could be performed in that particular area.

With a bacteriological can opener (Figure 5-21), remove circular disk, disk, about 1 to 1-1/2 inches (2.5-3.8 cm) in diameter, from center of bottom panel of container. Then, with metal cutters or tin snips, remove most of remainder of bottom, leaving about 1/2 inch (1.3 cm) border around outer edge of container. Empty and wash container with detergent and warm water; use a brush if necessary. Next, boil container in detergent and water to remove as much as possible of any product that may be trapped in the seam. Or place container in ultrasonic washer with detergent and wash at about 100-120ºF (37.7-48.9ºC) for at least 2 h. In either case, dry the container in an oven at about 100-120º F (37.7-48.9ºC) for at least 2 h.

Add distilled water plus wetting agent to a depth that just covers entire lid area. Place Plexiglas with tubing attached and wetted rubber gasket on open bottom of container. Begin with initial vacuum of 5 inches (127 mm), increasing gradually to maximum of 20-22 inches (508-558 mm). Swirl water in container to dissipate small bubbles produced by application of vacuum. Tilt container slowly to immerse all seam surfaces and scored area of the 405 container, letting light source focus through Plexiglas into can.

4. Other methods under development
1. Laser holographic method. This nondestructive optical technique uses an electronic processing system for leak detection of hermetically sealed containers. Wagner et al. (1981) studied the method and used it successfully to determine seal integrity of implanted cardiac pacemakers.

Hermetically sealed food cans are tested in a chamber (Figure 5-39) under either vacuum or pressure, by applying a predetermined amount of stress to cans. The can surface is viewed for fringes as the can ends deform in response to the applied stress. A hologram showing the image of fringes is recorded by a reflected laser beam of a subject illuminated by a portion of the laser beam. A hologram of cans within the test chamber is recorded on videotape and may also be exposed and developed in place with a liquid gate film holder. The pattern of fringes that occurs on the can surface indicates the relative size of the leak. To locate the leak, the stress applied to cans in the testing chamber is slowly varied, the seam area is photographically enlarged, and fringe control techniques are applied. Figure 5-40 is a Polaroid picture taken from a TV video monitor. The can on the left, which does not show fringes in the hologram, is the leaker.

1. Equipment for leak detection includes:
• Helium-neon laser, 5 milliwatts or 5 watts argon laser
• Test chamber
• Recording and display system
• Optical components

2. Helium leak test (U.S. Rhea and J.E. Gilchrist, FDA).(NOTE: This test is AOAC Final Action method 984.36, Official Methods of Analysis, 15th ed., 1990)

Flat cans are exposed to helium pressure in an enclosed tank for a specified period of time. Cans previously exposed to pressurized helium are observed for evidence of leakage: a swollen can is an indication of a leaker; a paneled can or a can with vacuum is usually not a leaker. Headspace gas is analyzed by gas chromatography to confirm the presence of helium. Cans with large amounts of internal air (e.g., dried or semidried products) are crushed by helium pressure and should not be tested by this procedure.

A swollen can is first depressurized, and, if necessary, a sample of the contents is removed for microbiological analysis. After resealing, the can is tested for a leak. Swollen cans may be sampled for headspace gas analysis by gas chromatography. The helium leak test detects holes as small as 1 µm. Results are reported as % helium in the headspace gas.

 
1. Equipment and materials
• Gas chromatograph (Figure 5-41) capable of separating and measuring nitrogen, oxygen, hydrogen, helium, and carbon dioxide
• Strip chart recorder or other readout system
• Puncturing press
• Helium exposure tank tested to 100 psi (690 kPa) (American Society of Mechanical Engineers paint tank, 10 gallon [38 L]) equipped with inlet and outlet micro control valves
• Pressurized helium tank with 2-stage regulator
• Pressure regulator
• Combination vacuum-pressure gauge for use on puncturing press Timer and solenoid to automate release of helium from exposure tank
• Helium gas standards
• Cyanoacrylate glue
• Can opener, bacteriological (Figure 5-21)
• Rubber disks, 2-3/8 ´ 1/8 inch (6.1 ´ 0.3 cm)

2. Procedure

Calibration of gas chromatograph. For gas chromatographs equipped with side port loop (0.5 ml), inject 5.0 ml calibrated helium standards (suggested range 5, 15, 25, 50, and 75% helium). For instruments not equipped with side port loop, inject appropriate volume of standards. Use same volume for analysis of headspace gas samples. Plot % helium vs. helium peak height at attenuation used. Depending on quality of instrument, plot should approximate a linear or continuous curve.

Helium exposure tank ( Figure 5-42). Control the rate of introduction of helium into exposure tank and time that cans are exposed to helium pressure at 45 psi (310 kPa). Timer, solenoid, and microvalves with Vernier scales can facilitate procedure. Connect helium source to exposure tank. Turn timer on to close outlet solenoid valve. Adjust inlet and outlet microvalves to settings of 0.25 and 0.5, respectively, on Vernier scale. At these settings, it should take about 20 min to reach 45 psi (310 kPa) in tank. Make minor adjustments if necessary. Adjust timer to expose cans to helium pressure at 45 psi (310 kPa) for 30 min, in addition to time necessary to reach 45 psi (310 kPa).

Sealing an open can ( Figure 5-43). A swollen can must be depressurized and resealed before exposure to helium. Release pressure by puncturing and, if necessary, cut hole 1.5 inches (3.8 cm) in diameter to remove sample for microbiological analysis as described in "Examination of Canned Foods". Depress any high edges and roughen area around hole with emery cloth. Pool glue (cyanoacrylate) around hole and press rubber disk 2-3/8 inches (6.1 cm) in diameter (1/8 inch [0.3 cm] thick) into glue. Take care to remove any air bubbles. Place weight (400 ml beaker filled with water) on disk for at least 1 h to obtain effective seal before exposure to helium.

Collection and analysis of headspace gas. After exposure to helium, make visual observation of cans( Table 5-1). Can piercing assembly is shown in Figure 5-44.Before piercing can, close gauge valve and pull plunger on syringe to remove air from silicone tubing. Close syringe valve and expel air from syringe. Puncture can and open gauge valve to read vacuum or pressure. Turn gauge valve and syringe valve to release gas into syringe. If gas sample is >5.0 ml, withdraw only 5.0 ml and inject into side port of gas chromatograph. If gas sample is <5.0 ml, force collected gas back into can. Close syringe valve to retain gas in tubing and can. Use syringe to add 40 ml room air to can, and pump syringe twice to mix gas. Let syringe equilibrate to atmospheric pressure and record syringe volume. From this dilute gas, obtain sample for gas chromatograph. Divide % helium measured by dilution factor to determine correct % helium in headspace gas. Use the following formula:

Dilution factor = (equilibrated syringe volume - 40 ml air + headspace volume)/(equilibrated syringe volume + headspace volume)

Example: (43 - 40 + 9)/(43 + 9) = 12/52 = 0.23 dilution factor % helium in can = % helium measured/dilution factor

Example: 5% helium/0.23 = 22% helium in can

 Measure headspace volume by piercing a control can that still has vacuum. Measure both amount of vacuum (inches or mm Hg) and volume of air pulled in from syringe.

Headspace volume = measured volume from syringe ´ 30 inches (762 mm) of mercury/measured vacuum in can in inches (mm) of mercury.

Example: If 6 ml air was pulled into can and vacuum was 20 inches (508 mm) of mercury:

Headspace volume = 6 ml ´ 30 inches (762 mm) Hg/20 inches (508 mm) Hg = 9 ml

For performing additional work on the can, the collected gas may be stored in a capped syringe for a few h without appreciable change in its composition.

Interpretation of results. Report can as leaker if, after exposure to pressurized helium, can internal pressure is £ 8 psi (55.2 kPa) or helium is ³1%. Report can as nonleaker if, after exposure to pressurized helium, can internal vacuum is ³5 inches (127 mm), or helium is <1%.

Contents

Examination of glass containers for integrity (Lin et al., 1998)

Almost all low-acid foods packaged in glass containers are sealed with vacuum-type closures. Currently 4 types of vacuum closures are widely used on low-acid food products: LT (lug-type twist) cap, PT (press-on twist-off) cap, pry-off (side seal) cap, and CT (continuous thread) screw cap (Figure 5-45). Packers' tests and examinations to ensure a reliable hermetic seal of containers are required by 21 CFR 113.60 (a) (2) and (3).
 
1. Visual examination for closure and glass defects (for definition of terms, see glossary at end of this chapter)
• cap tilt
• chipped glass finish
• cocked cap
• cracked glass finish
• crushed lug
• cut-through
• stripped cap

2. Seal integrity examination
1. Vacuum. Use standard open-closed type of vacuum gauge or USG No. 12118 gauge with both vacuum and pressure scales (Figure 5-46). Wet rubber gasket on piercing device with water. Shake off excess water. Puncture closure, using piercing needle attached to vacuum gauge. Read and record vacuum in inches (0-30 inches; 0-762 mm), or pressure (0-15 psi; 0- 103.4 kPa).
2. Removal torque (cam-off) for PT or LT type closures ( Figure 5-47). Properly secure jar on torque meter. Ease closures off in smooth, continuous motion rather than rapid, jerking motion. Use one hand to twist cap counterclockwise to open cap from sealed jar while avoiding any downward pressure on cap. Record maximum torque in inch-pounds (Newton meters) required to open cap.
3. Security values (lug tension) on lug-type twist cap ( Figure 5-48). Make vertical line on cap and corresponding line on container wall with marking pen. Turn closure counterclockwise just until vacuum is broken. Reapply closure to container just until gasket compound touches glass finish and closure lug touches glass thread (or until closure is at 2 inch-pound (0.23 Newton meters) reapplication torque to achieve uniformity for application). Measure and record, in 1/16 inch (1.6 mm) increments, distance in front of vertical lines that were made before opening. Security is considered positive if line on cap is to right of line on container, and negative if line on cap is to left of line on container.
4. Pull-up (lug position) for lug-type twist cap ( Figure 5-49). Mark vertical neck ring seam on glass finish. Measure distance from this vertical line, in 1/16 inch (1.6 mm) increments, to leading edge of cap lug position nearest it. Record lug position measurements made on right side of vertical neck ring seam (as analyst looks at package) as positive (+) and those to left side of parting line as negative (-).

Contents

Examination of Flexible and Semirigid Food Containers for integrity (Lin et al., 1998)

Flexible and semirigid food packages are composed mainly or in part of plastic materials. Closure is achieved by heat sealing or double seaming. The 4 main groups of packages that cause similar integrity concerns and that are examined by common methods are paperboard packages, flexible pouches, plastic cups and trays with flexible lids, and plastic cans with double-seamed metal ends.

The purpose of a hermetic closure is to provide a barrier to microorganisms and to prevent oxygen from degrading the food. Closure integrity is significant because sealing surfaces may contain food particles and moisture that contribute to heat-seal and double-seam defects. Critical control must be exercised in this operation. Visual examination will reveal most defects. For many flexible packages, seal strength may be ascertained by squeezing.

1. Package examination

Note condition of package (exterior and interior) and quality of seals or seams; observe and feel for gross abnormalities, mechanical defects, perforations, malformations, crushing, flex cracks, delamination, and swelling. Measure dimensions as recommended by manufacturer of closing equipment or packaging material. Perform teardown procedure as described. Note condition of package and closure. If there is evidence that a package may lose or has lost its hermetic seal, or that microbial growth has occurred in the package contents, further investigation is required.

1. Visual examination

Use hand as well as eye. A magnifying glass with proper illumination is helpful. Rub thumb and forefinger around seal area, feeling for folds and ridges. Rub fingers over flat surfaces to feel for delamination, roughness, or unevenness. By sight and touch, determine presence of defects. Mark location of defects with indelible ink. See Figure 5-50 for visual inspection criteria for closure seal.

2. Examination of packages (seeTables 5-12 and 5-13)

Table 5-12. Test methods for plastic packages containing food (Arndt, 1990).

Test methods	Packaging type
	Paper board	Flexible pouch	Plastic, heat-sealed lid	Plastic, double-seam metal end
Air leak testing	O	O	O	O
Biotesting	O	O	O	O
Burst testing	O	R	R	O
Chemical etching	O	O	O	NA
Compression, squeeze testing	R	O	O	O
Distribution (abuse) test	O	O	O	O
Dye penetration	R	O	R	O
Electester	O	NA	NA	NA
Electrolytic	R	O	R	NA
Gas leak detection	O	O	O	O
Incubation	R	R	R	R
Light	NA	O	O	O
Machine vision	O	O	O	O
Proximity tester	O	O	O	R
Seam scope projector	NA	NA	NA	R
Sound	R	NA	R	R
Tensile (peel) testing	NA	R	R	NA
Vacuum testing	NA	O	R	O
Visual inspection	R	R	R	R

Abbreviations: R, test method is recommended by NFPA Bulletin 41-L, Flexible Package Integrity Bulletin; O, other commercially accepted test method applications; NA, test method is inappropriate for this style package.

Table 5-13. List of visible package defects provided by National Food Processors Association (Arndt, 1990).
 

Defect	Package typea
	Paper board	Flexible pouch lid	Plastic, heat-sealed metal end	Plastic, double-seam
Abrasion	+	+	+	+
Blister	-	+	-	-
Burnt seal	-	-	+	-
Channel leak(er)	-	+	+	-
Clouded seal	-	+	-	-
Compressed seal	-	+	-	-
Contaminated seal	-	+	+	-
Convolution	-	+	-	-
Corner dent	+	-	-	-
Corner leaker	+	-	-	-
Crooked seal	-	+	-	-
Crushed	+	-	+	+
Defective seal	-	-	+	-
Deformed	+	-	-	-
Deformed seal	+	-	-	-
Delamination	+	+	+	+
Embossing	-	+	-	-
Flexcracks	-	+	+	+
Foreign matter (inclusion)	-	-	+	+
Fracture	-	+	+	+
Gels	-	-	+	+
Hotfold	-	+	-	-
Incomplete seal	-	-	+	-
Label foldover	-	-	+	-
Leaker	-	+	-	-
Loose flaps	+	-	-	-
Malformed	-	-	+	+
Misaligned seal	-	-	+	+
Nonbonding	-	+	-	-
Notch leaker	-	+	-	-
Puncture	+	+	+	+
Seal creep	-	+	-	-
Seal leaker	+	-	-	-
Seal with variation	-	-	+	-
Shrinkage wrinkle	-	-	+	-
Stringy seal	-	+	-	-
Swell (swollen package)	+	+	+	+
Uneven impression	-	-	+	-
Uneven seal junction	-	+	-	-
Waffling	-	+	-	-
Weak seal	+	-	-	-
Wrinkle	-	+	+	-

^a+, Definition is applicable to that package type; -, definition is not applicable.

1. Paperboard packages (NFPA, 1989)

Teardown procedures. Unfold all flaps (except gable top packages); check integrity and tightness of transverse (top and bottom) and side (vertical or longitudinal) seals by firmly squeezing package. If package has longitudinal sealing (LS) strip, pull off overlapping paper layer at side (longitudinal) seal. Check air gap of longitudinal sealing strip application (about 1 mm). Squeeze package and check that there are no leaks or holes in the LS strip. Next, on side opposite side seal, puncture container with sharp scissors and empty contents. Saving side seal portion, cut near fold at each end of package and down length of package to remove a large rectangular body portion. Observe this large rectangular body portion for holes, scratches, or tears anywhere on the surface. Pay close attention to corners of package, particularly directly under end seals and near the straw hole or pull tab, if present. Now cut remaining package in half through the center of the side seam. Wash both halves of remaining package and dry them with a paper towel. Mark to identify the package.

Evaluation procedures for seal quality differ between package designs, constructions, and sealing methods. Obtain specific procedures for a given package from the manufacturer. For example, seal evaluation may consist of starting at one end of the seal, and very slowly and carefully pulling the seal apart. In some packages the seal is good if the polymer stretches the entire length of the seal (that is, stretching of polymer film continues to a point beyond which paper and laminates have separated). In other packages, fiber tear can be seen the entire length of the seal (that is, raw paperboard is visible on both sides of the separated seal areas). This is known as 100% fiber tear and indicates a good seal. Test all 3 seals of each package half. Problems to look for are absence of (or narrow) fiber tear, lack of polymer stretch, "cold spots" (no polymer bond in seal area), and "tacking" (polymer melt but no stretch or fiber tear). For longitudinal sealing strip-type packages, additional tests (such as centering examination, heat mark examination, and appearance of aluminum foil examination when stripped) should be made according to manufacturer's directions.

Electrolytic and dye testing. These tests differ according to each system manufacturer's filed procedure. Contact the individual manufacturer, obtain recommendations, and follow them.

2. Flexible pouches (NFPA, 1989)
1. Teardown procedures. Check tightness of both head and side seals by squeezing each package from each fill tube or sealing lane. Important points are corners and crossing of head and side seals. This is a rapid determination of obvious defects. Each seal must be accurately torn apart and evaluated for correct integrity. Carefully inspect edges of each head and side seal for evidence of product in seal areas. No product should be visible.

Observe width of each seal area. Width must comply with machine-type specifications: for example, 1/16 inch (1.6 mm) minimum on all head and side seals for fill tube or sealing lane machines. Look for presence of smooth seal junction along inside edge of seal. Open each package to check side seals and head seals. Visually inspect for such defects as misaligned seal, flex cracking, nonbonding, and seal creep. If applicable, tear the seals by doing a seal tensile strength test or a burst test. Then observe appearance of tear at each seal. Seals should tear evenly so that foil and part of laminated layer from one side of package tears off, adhering to seal on other side of package. The seal should appear rough and marbleized. The seal is also adequate if the foil is laid bare across entire length of seal. Retain records of test results as required.

2. Other test procedures

Squeeze test. Apply manual kneading action that forces product against interior seal surface. The sealing surface must be smooth, parallel, and free of wrinkles. Examine all seal areas for evidence of product leakage or delamination. Packages that exhibit delamination of the outer ply on seal area but not at product edge should be tested further by manually flexing the suspect area 10 times and examining all seal areas for leakage or reduction in the width of the seal area to less than 1/16 inch (1.6 mm).

Seal tensile strength. Results to be expressed in pounds per linear inch, average of sample (that is, 3 adjacent specimens cut from that seal) should not be less than specified for the material and application.

Burst strength test. With internal pressure resistance as the measurement to check all seals, apply uniform pressure, under designated test conditions, to a level of not less than specified for a material or application, for 30 s. Then evaluate seals to ensure that proper closure seal is still in effect.

3. Plastic package with heat-sealed lid (NFPA, 1989)

Container integrity testing. Peel test procedures of form fill and seal containers. Squeeze container sidewalls of entire set from a mold. Squeeze each cup to cause 1/8 inch (3.2 mm) bulge of lid area. Lid should not separate from package when package is squeezed. Observe sealing area for fold-over wrinkles in sealant layer of lidstock. From a first set of containers, visually observe embossed ring in sealed area for completeness. (Embossed ring should be at least 90% complete if present.) Remove a second set of containers (1 cup per mold) and gently peel back each lid at approximately a 45ºangle. Observe the peeled area for a generally frosty appearance on both the lid and cup sealed surfaces. Observe entire package for holes, scratches, even flange widths, smooth inside surfaces, and any deformities caused by dirty mold or sealing die.

Leak test procedures (optional). These tests differ according to each system manufacturer's filed procedure. Contact the individual manufacturer, obtain recommendations, and follow them.

Electrolytic test. Plastic packages generally do not conduct a flow of low-voltage electricity unless a hole is present. Use a volt meter or amp meter to determine the presence of a closed circuit. If a voltage flow can be measured, use a dye solution to identify the presence of a hole.

Dye penetration test. Use a dye to locate leaks in packages or to demonstrate that no leaks exist.

Air pressure or vacuum test. Apply pressure or vacuum to a closed package to test for holes and to observe any loss of pressure or vacuum. Underwater vacuum testing may reveal a steady stream of small bubbles emitting from a hole in a package.

4. Plastic cans with double-seamed metal ends (NFPA, 1989)

Procedures for examining metal cans with double seams are described in this Chapter and in 21 CFR, Part 113. Use these methods to examine plastic cans with double-seamed metal ends. Make the following changes to 21 CFR 113.60 (a,1,i,a and b).

2. Micrometer measurement system

Metal cans. Required: cover hook, body hook, width (length, height), tightness (observation for wrinkle), and thickness. Optional: overlap (by calculation) and countersink.

Plastic cans with double-seamed metal ends. Required in addition to seam scope examination: thickness and tightness. Compare seam thickness to that calculated from individual thicknesses of plastic flange and neck and metal end, excluding compound. Optional: cover hook, countersink, and width (length, height).

Seam scope of projector

Metal cans. Required: body hook, overlap, tightness (observation for wrinkle), and thickness by micrometer. Optional: width (length, height), cover hook, and countersink.

Plastic cans with double-seamed metal ends. Required: overlap, body hook, countersink, width (length, height). Optional: cover hook.

Visual examination for plastic cans with double-seamed metal ends. Required: tightness. Note compression of pressure ridge or flange during overlap measurement. Remove entire cover and examine pressure ridge for continuity. Under 21 CFR 113.60 (a,1,i,c) add the following: pressure ridge for plastic cans with double-seamed ends; impression around complete inside periphery of can body in double seam area.

3. Microleak detection

Microleak testing methods are not listed in order of sensitivity, nor is it necessary to use them all. Each test has advantages and disadvantages, depending on the package, equipment, and set of conditions. Optional methods are appropriate when additional information will clarify the nature of various package defects. Some test methods are not appropriate for some package materials, closures, or package styles. Refer to the manufacturer of the package or closure system for recommended test methods or see Table 5-12. Common methods are presented to provide the analyst with procedures and options. Visible defects of the 4 flexible package groups are summarized in Figure 5-50.

Measure packages before testing for microleaks. Mark visually detected defects to aid location during or after microleak testing (non-water soluble markers are recommended). Record all results, methods used, and environmental conditions (temperature, relative humidity) and retain these records. Conduct all tests in the standard laboratory atmosphere of 23 ± 2ºC and 50 ± 5% relative humidity. When this is not possible, report temperature and relative humidity along with test results (ASTM, 1992a).

1. Airleak testing (Arndt, 1990) (Figure 5-51)
1. Dry method
1. Materials
• Compressed air with regulator
• Needle, valve, hoses
• Pressure gauge or flow meter

2. Procedure

Puncture container wall with needle. Inject air while increasing at 1 psi/s (6.9 kPa/s) until a standard pressure is reached. Standard pressure used for testing should be less than the normal unrestrained burst pressure for the package. Observe pressure gauge for loss of internal pressure over a 60 s period. If a flow meter is used, observe for airflow, which indicates presence of openings in the test package. Dye testing may be used to locate air leaks that are not visible with the dry method. Inject air to create internal pressure within the package without causing it to burst. Observe all surfaces and seals for air leaks. Observe flow meter for indication of air loss from the package.

2. Wet method
1. Materials
• Compressed air with regulator
• Needle, valve, hoses
• Water
• Transparent container to observe bubbles

2. Procedure

Inject air to create internal pressure within the package without causing it to burst. Immerse package in water and inspect visually for a stream of bubbles emitting from a common source.

3. Results

Positive. - A steady stream of bubbles comes from the package at one or more locations.

Negative. - No bubbles are emitted from the package.

False positive. - Bubbles are emitted from point at which needle entered package; or bubbles cling to surface of the package after package is submerged in water.

False negative. - Food particles block holes through which air might escape from defective package; or air pressure used is insufficient to force air through minute holes in package.

2. Biotesting (Arndt, 1990; Wagner, 1981) (Figure 5-52)

The objective of biotesting is to detect the presence of holes in hermetic packages by placing them in an agitated solution of fermentation bacteria in water for an extended period of time.

Obtain representative packages and submerged them in an agitated solution of active bacteria. The bacterial concentration should be >107 /cm2 . The temperature of the solution that surrounds the packages should be maintained at a temperature that permits rapid growth of the bacteria within any packages they may enter. However, growth of the bacteria in the liquid surrounding the submerged packages is not desirable. The bacteria must cause fermentation of the product within the package if they penetrate and must not be pathogenic. Packages should be flexed during immersion to expose cracks and holes to incursion. The solution that surrounds the packages should be maintained at a temperature that permits rapid growth of bacteria within defective packages. After biotesting, packages are incubated for 3 weeks at 95-100ºF (35-37.7ºC). This test should be used only to evaluate new package designs or to validate packaging systems. It should not be used as routine quality control procedure. Other methods are cheaper, simpler, and just as reliable.

1. Materials
• Water bath with temperature control and agitation solution of Enterobacter aerogenesfor foods, pH > 5.0. Solution of Lactobacillus cellobiosisfor foods, pH £ 5.0
• Sample packages
• Apparatus to flex packages
• Incubator

2. Procedure

Obtain representative samples. Mix active bacteria in water at about 1.0 ´ 107/ml. Immerse samples in mixture. Agitate water bath and flex sample for 30 min. Remove packages and rinse with chlorinated water. Incubate samples for 2 weeks at 95-100ºF (35-37.7ºC). Observe packages for swelling for 3 weeks. Open each package by cutting in half across the middle, leaving a hinge and observe contents for spoilage. Thoroughly wash insides of both halves from each spoiled package. Subject each half to a dye test to locate leaks.

3. Results. Report location of leaks.

3. Burst testing (Arndt, 1990) (Figures 5-53 and 5-54)

The objective of burst testing is to provide a means for determining the ability of a hermetically sealed package to withstand internal pressure (psig, Pa). The entire package is subjected to uniform stress and failure generally reveals the weakest point. Both restrained and unrestrained burst testing may be used. Restraint limits expansion by minimizing the angle of the package seal, which becomes greater as a package is inflated. With restraint, packages with strong seals fail at greater internal pressure than do packages with weak seals. Thus, use of a restraining device during burst testing permits noticeable separation between packages having strong or weak seals.

Fused seals are stronger than the walls of a flexible package. Burst failure generally occurs adjacent to fused seals. Peelable seals are weaker than the walls of a flexible package, and less pressure is needed to induce pressure failure. Lower pressure and a longer time increment are required to burst test peelable seals.

Dynamic burst testing involves a steady increase of internal pressure until failure occurs. Static burst testing involves a steady increase in internal pressure to a pressure less than failure, followed by a 30 s hold. Both methods are used for packages with fused seals. Peelable seals are burst-tested by inflating at a steady rate to a point less than failure pressure and held for 30 s, followed by a 0.5 psig (3.4 kPa) pressure increase and another 30 s hold. Pressure and time indexing is continued with observation of the seal area for seal separation (peeling) until failure occurs.

1. Materials
• Compressed air or water
• Regulation valve
• Needle with gasket and pressure tubing
• Solenoid with timer(s)
• Pressure indicator(s), digital or gauge with sweep hand
• Restraining device (optional)

2. Procedure

Use empty sealed package, or cut and remove contents of a filled package. Place package in restraining fixture (if used). Pierce package with gasketted needle(s) and inject air or water. Inflate at 1 psig/s (6.9 kPa/s).

Dynamic method. Continue inflation at 1 psig/s until failure occurs. Record internal pressure at failure.

Static method. Inflate at 1 psig/s (6.9 kPa/s) to specified internal pressure, and hold at specified pressure for 30 s. Record as pass or fail.

Indexed method. Inflate to 5 psig (34.5 kPa) and hold for 30 s, inflate additional 0.5 psig (3.4 kPa) and hold for 30 s. Continue increase and hold sequence until failure occurs. Observe peelable seal separation. Report internal pressure at failure.

3. Results

Positive. Pressure failure occurs below specified level of performance, indicating a hole in the package.

Negative. No pressure failure occurs below specified level of performance.

False positive. A leak is present at point where air or water is injected into package and pressure cannot be maintained.

False negative. A small leak occurs, but is not sufficient to reduce pressure noticeably.

4. Chemical etching (Arndt, 1990)

Multilaminate and composite packaging materials may be etched to remove overlying layers, revealing the hermetic seal of packages that have polyolefin heat seals. This allows comparison of visually detected package defects on the external surface before etching and within the seal area after all external layers have been removed.

Composite paperboard packages. The outer layers of a package are removed by tearing, abrasion, and chemical action to expose the sealant layer intact. By photographing or photocopying the package before etching, the etched seal can be compared with the photograph to determine the significance of visually discernible defects.

1. Materials
• Water bath and heater with thermostat
• Three l-L Pyrex glass beakers
• Running tap water
• Graduated cylinder
• Automatic stirring device (heated is preferred)
• Drying oven equilibrated to 65ºC (150ºF)
• Paper towels
• Rubber gloves, protective goggles, apron, tongs
• Fume hood with chemical-resistant surface
• Chemicals for etching of paperboard aseptic packages:
• hydrochloric acid (HCl) solution, 3.7 N
• acidified solution of copper chloride (CuC1₂)
• saturated solution of bisodium carbonate (Na₂CO₃) in water

2. Preparation of solutions.CAUTION: Always pour acid into water; never pour water into acid.

Pour 0.5 L of concentrated HCl into 1 L of cold distilled water. Pour slowly, as heat will be produced when acid and water mix. Stir until mixed completely. Cover to prevent evaporation. Solution will be 3.7 N HCl. Pour 0.5 L of concentrated HCl into 1.5 L of cold distilled water. Add 10 g of CuC1₂. Stir until completely mixed. Cover beaker and let warm to room temperature before using.

Pour enough Na₂CO₃ into a container to make a saturated solution at room temperature. Some undissolved Na₂CO₃ should remain on bottom of beaker after stirring.

3. Procedure

Cut transversal seal from package approximately 1 inch (2.5 cm) from end. Identify multiple samples by notching cut edge with scissors. Manually strip paper from sample to be etched. Place sample in hot HCl solution (65º C) for 5 min. Remove sample with tongs and immerse it in Na₂CO₃ solution to neutralize the acid. Remove sample from the Na₂CO₃ solution with tongs and rinse it in running tap water. Pull off polyethylene layer that lies between paperboard layer and aluminum foil.

Using a glass stirring rod to manipulate the sample, drop it into the CuC1₂ solution so that it is completely immersed. Observe closely while stirring to ensure that the heat of the reaction does not damage the polyethylene sealant layer as the foil is dissolved. Remove from solution.

Dip sample in Na₂CO₃ solution to neutralize it, and then rinse it with water. Press sample gently between soft absorbent paper towels and place in oven at 65ºC (150º F) until dry. Apply alcohol-based dye solution to inner and outer seal edges. (See fluorescein dye solution formula , described above).

Observe pattern of ink dispersion and check for leaks and channels within fused seal area. Use overhead projector to enlarge seal samples and provide a more accurate visual inspection.

Retortable pouches (Figure 5-55)

1. Materials
• Two l-L Pyrex beakers
• Running tap water
• Paper towels
• Rubber gloves, apron
• Protective goggles, tongs
• Fume hood with chemical-resistant surface
• Chemicals for etching retortable pouches
• 6 N HCl solution, commercial grade Tetrahydrofurant (THF), commercial grade, stabilized

2. Procedure

Cut off end of pouch and remove contents. Wash inside of pouch. Dry the pouch. Cut all but suspected area away from area of interest, leaving about 1 inch (2.5 cm) adjacent to seal. Soak sample in tetrahydrofurant (THF) to remove outer polyester layer by softening adhesive and/or inks. Do this in a fume hood; wear protective gloves resistant to THF. (If separation cannot be obtained, proceed to next step.) Remove most of the ink and adhesive from aluminum foil with THF and paper towels. Soak remaining structure in 6 N HCl in a fume hood to remove aluminum foil by etching. Rinse sealant layers with water and dry with paper towels.

5. Compression test (Arndt, 1990) (Figure 5-56)

Place a filled and sealed food package on flat surface and apply pressure while observing for leaks.

1. Materials
• Flat surface or conveyor belt
• Sealed package
• Heavy flat object or mechanical press
• Timer

2. Procedure

Static method. Place sealed package on flat surface and lay a flat-surfaced weight on it. Observe effect of weight on integrity of package seals over time. A similar test may be performed by applying a constant weight to a package moving on a conveyor belt. The speed of the moving belt determines the time of compression.

Dynamic method. Use a press to continually increase the force applied to a package at a constant rate. Observe the maximum force required to cause failure of the package.

Squeeze test. Apply a manual kneading action that forces product against the interior seal surface area. Examine all seal areas for evidence of product leakage or delamination. Packages that exhibit delamination of the outer ply on the seal area but not at product edge should be tested further by again manually flexing the suspect area 10 times and examining all seal areas for leakage or short-width.

3. Results

Positive. Holes form in package or its seals or seams, with measurable movement of top plate or deflection on a force gauge.

Negative. No loss of hermetic integrity, and no measurable movement of top plate or deflection on a force gauge.

False positive. Underfilled or weak packages deflect in a manner that simulates failure without loss of hermetic integrity.

False negative. Holes form in package but food product closes off the holes, permitting pressure to increase within package.

6. Distribution (abuse) test (Arndt, 1990)

Packages are subjected to vibration, compression, and impact at levels typical of the distribution system for which they are designed. After the test, which is a conditioning regimen, the packages are examined. Defects are quantified and described in relation to package failures observed in normal distribution. Fragility is eliminated by design changes in the package system. Whenever possible all samples should be incubated for 2 weeks at 100º F (37.7ºC) before abuse-testing (Figure 5-57).

1. Materials
• Packages to be tested
• Drop tester
• Vibration table
• Compression tester
• Standard laboratory conditions 23 ± 2º C, 50 ± 5% relative humidity
• Incubator at 100º F (37.7ºC) to contain all test packages

2. Procedure. See ASTM D-4169 Standard Practice for Performance Testing of Shipping Containers and Systems (ASTM, 1992b).

Select distribution cycle 6 for flexible packages in shipping cases transported by motor freight. Before testing, incubate all packages for 14 d at 100º F (37.7ºC) and inspect visually for defects.

Perform the following 10 steps (see Section 9 of ASTM D-4169) (ASTM, 1992b).

1. Define shipping unit - Shipping unit to be tested is a typical pallet load.
2. Establish assurance level - Assurance level II will be used, based on value and volume of shipment.
3. Determine acceptance criteria at assurance level II:

Criterion 1- no product damage;
Criterion 2- all packages in good condition.
4. Select distribution cycle (DC) - DC-6 will be used for pallet shipments.
5. Write test plan (values for X must be determined before conducting the test). Select representative samples for test. Condition samples to 23 ± 1ºC, 50 ± 2% relative humidity, in accordance with Practice D 4332 (ASTM, 1992a).
6. Perform tests in accordance with test plan in step 5, as directed in the referenced ASTM standards and in the special instructions for each shipment.
7. Evaluate results - Examine products and packages to determine if acceptance criteria have been met.
8. Document test results (ASTM, 1992c) - Write a report to cover all steps in detail.
9. Report fully all the steps taken. At a minimum, the report should include all the criteria in step 10.
10. Description of product and shipping unit DC and test plan Assurance levels and rationale
• Number of samples tested
• Conditioning used
• Acceptance criteria
• Variation from recommended procedures
• Condition of specimens after test

After testing, examine all failed (positive) packages to determine location and cause of damage. Incubate all containers that do not fail (negative) during testing for 14 d at 100º F (37.7ºC) and inspect visually for defects before destructive testing by other methods listed in this chapter.
3. Results

Positive. A package loses hermetic integrity during any one phase of the testing protocol or during the incubation period that follows:

Type test: Handling (ASTM, 1992d)
ASTM Method: D-1083
Level: One impact on 2 opposite base edges from X inches

Type test: Stacking (ASTM, 1992e)
ASTM Method: D-642
Level: Compression to X lb (individual container). Alternative full pallet load compression test, X lb per bottom tier container.

Type test: Vibration (ASTM, 1992f)
ASTM Method: D-999, Method C
Level: Search 3-100 Hz at 0.5 g peak. Dwell 10 min at 0.5 g peak

Type test: Handling
ASTM Method:

 
D-959 (ASTM, 1992g)
D-1083 (ASTM, 1992d)
D-997 (ASTM, 1992h)
D-775 (ASTM, 1992i)

Level: One impact on 2 opposite base edges from X inches

Type test: Stacking
ASTM Method: D-642 (ASTM, 1992e)
Level: Compression to X lb (individual container). Alternative full pallet load compression test, X lb per bottom tier container.

Negative. A package retains hermetic integrity through the test, and contents do not show evidence of microbial growth after incubation.

False positive. A package appears to be defective, yet confirmational testing by incubation or dye penetration reveals that no loss of the hermetic barrier occurred during the abuse test.

False negative. A package appears to pass testing but later exhibits failure when incubated.

7. Dye testing (Arndt, 1990)

Dye or ink is applied to inside surface of a cleaned package at the seal or suspected location of failure and observed to determine whether it can pass through to the outside(Figures 5-44, 5-58, 5-59).

1. Materials
• Disposable plastic gloves
• Dye solution: 1 L of isopropanol (solvent) and 5 g of rhodamine (powder) mixed (or other appropriate dye solution
• Sink
• Scissors or knife
• Oven to dry sample packages
• Paper towels
• Magnifying glass or low-power microscope

2. Procedure

Open and empty a package; wash, and dry by wiping or by oven drying (180ºF (82.2ºC), 15 min). Apply low surface-tension solution containing dye along the closure or on side of package at suspected location of hole. The solution moves by capillary action through the hole and appears on opposite side of package wall. After dye is completely dry, cut package with scissors and examine the hole closely.

Cut open cans, tubs, or bowls through bottom (leaving seal areas or double seams untouched) and remove product. Cut pouches and paperboard containers along equator, leaving a hinge (so that both ends can be tested), and remove product. Wash package with water containing mild detergent, rinse thoroughly with tap water, and wipe dry. Holding package upside down and at slight angle, place 1 drop of dye solution at inside edge of seal surface. Rotate to allow dye to wet entire inside seal circumference.

CAUTION: A number of dyes are known or suspected to cause cancer. Rhodamine B is a possible carcinogen. Wear disposable plastic gloves and avoid skin contact with dyes.

Let dye solution dry completely. Very slowly peel the seal completely and observe the frosty, white, sealed surfaces for evidence of dye. In some packages the innermost laminates must be carefully observed for stretching as the seal is peeled.

3. Results

Positive. Dye penetrates hole in package, indicating loss of hermetic barrier.

Negative. Dye does not pass through the package (wall or seal).

False positive. Solution dissolves packaging material, creating hole in package, or dye is accidentally splattered on outside of package, indicating hole or leakage where none exists.

False negative (for paperboard only).Solution penetrates holes in hermetic barrier layers but fails to reach outside of package where it would be visible.

8. Electester (Arndt, 1990)

The objective is to determine changes in viscosity of liquid foods after incubation of filled packages (Figure 5-60).

Microbial fermentation can cause changes in the viscosity of still liquids. If all factors are constant, shock waves will dampen at different rates in liquids with different viscosities. Incubation of shelf stable liquid foods and nondestructive testing of each package may identify containers that have been subjected to microbial activity.

1. Materials
• Packages filled with still, liquid food, incubated
• Electesting device
• Fixture to restrain test packages

2. Procedure

Remove representative samples from production line and incubate at 95ºF (35ºC) for 4 d. Place packages containing still liquids in restraining device with largest flat surface of package facing downward. Rotate package 90º horizontally and back to its original position very rapidly; do this only one time. The motion creates a shock wave. Fixture holding the package is precisely balanced to minimize outside interference and minimize dampening as shock wave moves back and forth within package. Motion is sensed and displayed on an oscilloscope with alarms alerting operator to vibrations that dampen more quickly or more slowly than normal for a specific liquid food product. Examine contents with a microscope and determine pH to confirm spoilage if there is any doubt.

3. Results

Positive. Wave dampens more quickly or slowly than normal, indicating change in product viscosity.

Negative. Rate of wave dampening is within range established by testing "normal" liquid product that did not display microbial spoilage during incubation.

False positive. Range of acceptance is too narrow, and normal product is incorrectly identified as spoiled.

False negative. Range of acceptance is too broad, and spoiled product is incorrectly identified as normal.

9. Electroconductivity (Arndt, 1990)

The objective is to detect holes in hermetic packages by sensing the flow of electrical current. Plastics are generally poor conductors of electricity. Consequently, plastic food packages without holes will form an effective barrier to mild electrical current; therefore, this method may be used to detect minute breaks in plastic food packages. A detectable flow of low-voltage electrical current generally indicates that the hermetic barrier has been lost.

1. Materials
• 1% NaCl in water (brine solution)
• Scissors
• Battery 9V, three 12 inch (30.5 cm) lengths of wire, 9V light bulb, or a conductivity meter (VOM). Remove insulation from each end of wires. One wire from positive pole goes to light bulb that has a wire as probe. The second wire from the negative pole is the other probe (Figure 5-61).
• Plastic bowl large enough to submerge package

2. Procedure

Obtain sample food package and cut off one end with scissors. Aseptic paperboard packages and flexible pouches may be cut on all but one edge along package equator and folded 180º on uncut side to form 2 equal halves. Wash samples to remove all food contents and any dried plugs that may occlude holes. Oven drying at 180ºF (82.2ºC) is recommended but not required before immersion. Wipe the cut edges with a paper towel if necessary, as wet edges may result in false-positive test results. Place samples in bowl containing brine solution and partially fill sample with brine so that it stands upright and is almost completely submerged. Place conductivity meter or light bulb with one probe inside the package and the other outside the package. Submerge both probes into their respective brine solutions. Test the other half of package similarly for current flow.

3. Results

Positive. Current flow indicates break in hermetic barrier.

Negative. No current flow indicates hermetic barrier exists.

False positive. Aluminum foil conducts electricity. A pinhole or partial break through inner layers of a package may expose the foil layer, resulting in false-positive test result. Dye testing will confirm presence or absence of holes. Moisture may form a bridge over cut edge of a package, creating a false positive.

False negative. Dried product may occlude minute holes in a package. If plugs do not rehydrate quickly, they will not conduct electricity when packages are immersed.

10. Gas detection (Arndt, 1990)

The objective is to detect microleaks in hermetically sealed packages with sensors tuned to detect only gas leaking from within package. The package must be a barrier to the test gas so that the rate of gas permeation through the package wall will not raise the normal background concentration in atmosphere of testing area. Gas concentrations may be detected by impact to a sensor. The sensor may be a heated element in which electrical resistance varies in relation to gas molecules removing heat as they impact. Examples of test gases suitable for package include oxygen, nitrogen, hydrogen, carbon dioxide, and helium.

1. Procedure for detecting helium leak

Gas obtained from storage tanks or air fractioning may be used to displace headspace gases within food packages before closure. Concentration of gas within package must be greater than the concentration of that gas in the atmosphere where packages are tested. There are three modes for detection: ASTM E493, inside-out tracer mode (ASTM, 1980a); ASTM E498, tracer probe testing mode (ASTM, 1980b); and ASTM E499, detector probe testing mode (ASTM, 1980c). Slight compression of a package may assist the movement of gas molecules through microleaks.

2. Results

Positive. Detection of gas concentrations greater than the normal atmospheric concentration indicates break in hermetic barrier of sample package. Confirm with dye testing to locate hole in sample package.

Negative.No detection of test gas concentration greater than the normal atmospheric concentration indicates hermetically sealed container.

False positive.Detection of gas concentrations in excess of the normal background level may result from increase in test gas concentration in the testing area. Test background concentration before and after testing sample. Packages with high permeability may lose gas.

False negative. Internal gas concentration may be reduced through absorption by the product, reaction with a component inside the package, or permeability if over an extended storage period.

11. Incubation (Arndt, 1990)

The objective is to determine whether a package has lost hermetic barrier by holding containers at an ideal temperature for sufficient time to ensure microbial growth. Hermetic integrity is the condition that bars entry of microorganisms into a package. Growth of microorganisms indicates either insufficient processing or loss of hermetic barrier. Growth may be observed as gas formation, change in pH, growth of viable organisms, or changes in the appearance of food.

1. Materials
• Insulated box or room to serve as an incubator
• Heater with thermostat
• Storage racks
• Recording thermometer
• Temperature recording charts
• Knife, scissors
• pH meter
• Inoculating loop and flame
• Sterile culture dishes and tubes, and culture media

2. Procedure

Obtain representative sample packages containing processed product. Inspect all samples visually for defects. Place packages in incubator for recommended period of time at recommended temperature.

Products stored in incubator at 95ºF (35ºC)

• FDA products - 14 d
• USDA products - 10 d

Products stored in warehouse
• 85-95ºF (29-35ºC) 30 d
• 70-85ºF (21-29ºC) 60 d
• 60-70ºF (16-21ºC) 90 d

Visually inspect packages for evidence of spoilage. Open and inspect all (or some) packages for visible signs of microbial growth, aroma, and change in pH. Never taste incubated product if spoilage may have occurred. Aseptically obtain product samples to culture microbiologically and confirm cause of spoilage. Conduct appropriate integrity test on package to identify presence or absence of microleaks. Dispose of product safely. Autoclave any product or packages showing spoilage before disposal.
3. Results

Positive. Spoilage has occurred and is evident as swelling, putrefactive odor, change in product pH from normal, or change in appearance.

Negative. Spoilage has not occurred.

False positive. Chemical reaction or enzymatic activities alter product characteristics without microbial activity.

False negative. Should not occur because this would be commercial sterility.

12. Light (Arndt, 1990)
1. Infrared light. The objective is to observe differences in the absorbance and transmittance of heat energy (infrared light) in a package or seal. Infrared light may be absorbed, transmitted, and emitted by a package or a seal. Differences between these parameters provide a means for visual interpretation when sensed automatically and enhanced for visibility.
1. Materials
• Infrared light or oven (180ºF, 82.2ºC)
• Visual infrared light detector

2. Procedure: Expose samples to infrared radiation before examining.

2. Laser light. The objective is to measure small changes in the relative position of similar surfaces on separate packages as they are subjected to changes in external pressure. Flexible packages possessing some headspace gas may be flexed by altering the external pressure in a closed chamber. Packages are held by fixtures so that a split laser beam may be directed to the same position on both packages. The reflected beams are recombined with mirrors and prisms. Laser light has a well-defined wavelength that does not change by reflection. However, if packages move differently when flexed, one beam segment will travel a greater distance than the other. When beam segments are recombined, differences in position of reflecting surfaces will cause the recombined laser beam to be out of phase. This condition can be sensed and used to segregate packages that do not flex in the normal manner from those that do.
1. Materials: Laser set up with chamber and means to read the differences.
2. Procedure: Flex packages in chamber by applying and releasing vacuum. Observe any difference in the 2 packages and determine by controls which package leaks.

3. Polarized light. The objective is to observe differences in the transmittance of visible light through translucent and transparent heat seals (Figure 5-62). Polarized light filters are composed of minute parallel lines on a glass surface or plastic film. When 2 polarized filters are rotated to be 90° different, no light will pass through. At 0°, both sets of lines are parallel and a light bulb set in line with the 2 polarized filters will be visible.

During heat sealing of transparent and translucent plastic materials, energy is added, providing free movement of polymer chains. Close packing and increased hydrogen bonding occurs, resulting in alignment of carbon chains and increased crystalline structure. Differences between random, oriented, and crystalline configuration affect both light absorption and transmission in these materials. A seal sample placed between 2 polarizing filters is first illuminated by polarized light. To enhance color changes resulting from differences in crystalline structure, rotate the other filter to block most of the transmitted light. Inspect visually to determine degree of crystalinity within fused seals. Uniform crystalinity, seen as uniform color tone along the inner edge of the primary seal, is one indicator of fusion. Areas that are not fused appear as a different color. Colors differ with materials and thickness.

1. Materials
• Light bulb, white, 40, 75, 100 W
• Polarized camera filters, 2 each
• Frame to hold filters and permit free rotation of both filters in line with light bulb and sample

2. Procedure

Obtain a clean transparent seal sample. Turn on light. Place seal sample between polarized filters. Rotate one filter to obtain maximum difference in color between fused seal and nonseal area. Examine fused seal area for uniformity.

4. Visible light. The objective is to detect holes in packages by sensing transmitted and reflected visible light. Package is placed over low-wattage light bulb in darkened room to enhance visual inspection. Aluminum foil will block all light transmission except where holes and flexcracks in foil are present. Close inspection is required to determine whether other lamina overlay holes in foil layer. Dye testing is required to establish presence or absence of minute holes. Chemical etching may be used to remove materials external to polyolefin seals. Magnification of etched seals with backlighting aids inspection.
1. Materials
• Light bulb
• Scissors
• Sink with running water
• Paper towels
• Darkened room
• Indelible marking pen
• Dye (optional)

2. Procedure

Remove contents, wash, and dry container. Inspect package for light leaks. Mark location of light leaks with a marking pen; draw a circle around the defect location. Closely examine defects for presence of holes through all layers. Use dye test to verify presence or absence of holes.

3. Results

Positive. A hole through all layers is detected in a package.

Negative. No light leaks are detected.

False positive. A hole in the foil layers permits light to pass, but no holes exist in overlying layers and hermetic barrier is maintained.

False negative. A hole through all layers is not aligned so that light can be transmitted.

13. Machine vision (Arndt, 1990)

The objective is to detect holes in hermetic packages by computer evaluation of images with previously defined patterns of acceptance. This system is designed to eliminate visual inspection of packages. Packages are positioned before a camera to present a consistent pattern. The video image obtained is digitized. Both grayscale and color density may be evaluated. The computer compares coded patterns with acceptable patterns stored in memory. Some systems evaluate one image at a time. Others use parallel computers to evaluate different segments of the video image in less time. Patterns that do not match the acceptance criteria are rejected and the package is automatically rejected from the production line.

1. Materials
• Video imaging system
• Computer with stored images for acceptance criteria
• Strobe light (optional)
• Packages

2. Results

Positive. Image does not match acceptance criteria.

Negative. Image matches acceptance criteria.

False positive. Image was not presented to camera correctly and does not match acceptance criteria.

False negative. Acceptance criteria include defects.

14. Proximity devices (Arndt, 1990)

The objective is to detect holes by measuring changes in the shape of hermetically sealed packages as a function of time. The position of a package containing metal may be established by the strength of a magnetic field, detected with a galvanometer. By comparing 2 readings as a function of time, a determination can be made as to whether the shape of a package has changed.

1. Materials
• Proximity detection system
• Computer with stored acceptance criteria
• Packages

2. Procedure

Compare multiple packages to a standard value. Fix limits of acceptance or alter automatically by computing a running average and standard deviation. Packages displaying stronger or weaker disturbances to a magnetic field sensed by a galvanometer may fall outside of the limits of acceptance. Mark these packages for removal from packaging line.

Read magnetic fields of single packages at one location and, after a period of time, make a second reading at a downstream location. If shape of container changes, mark package for removal from packaging line. Confirm with dye testing to locate holes in packages.

3. Results

Positive. Disturbance of magnetic field exceeding limits of acceptance.

Negative. Disturbance of magnetic field within limits of acceptance.

False positive. External disturbance of magnetic field or imprecise positioning of package resulted in values that exceeded limits of acceptance.

False negative. Distortion of package sufficient to cause disturbance of magnetic field outside normal range of acceptance.

15. Seam scope projection (Arndt, 1990)

The objective is to measure critical dimensions in the closure profile of plastic packages. Packages are cut in cross-section to reveal all components in their proper thickness and relative position. The cut edge is magnified with a projector to aid measurement and visual inspection.

1. Materials
• Knife, saw, or scissors
• Microprojector
• Micrometer, calipers, ruler, or measurescope

2. Procedure

Cut directly across seal or closure with knife, saw, or scissors and remove section containing adjacent material. Magnify cross section. Compare observed dimensions with criteria for acceptance or rejection provided by manufacturer of package or closure machine. Accept or reject sample.

3. Results

Positive. Dimensions of sample exceed limits of criteria for acceptance.

Negative. Dimensions within limits of criteria for acceptance.

False positive. Magnification with incorrect scale or measuring error results in rejection of acceptable sample.

False negative. Measuring error results in acceptance of defective sample.

16. Sound (Arndt, 1990)

Ultrasonic. The objective is to passively sense air moving through small orifices in packages possessing internal vacuum or pressure by monitoring the presence or absence of high-frequency sound waves.

1. Materials
• Microphone
• Audiofilters
• Oscilloscope with alarm system
• Packages

2. Procedure

Place packages in a chamber to eliminate external disturbances and subject to changes in external pressure. Air movement through small holes in package wall generates ultrasonic sound waves. A microphone senses the vibration. Audiofilters eliminate all frequencies except those of interest.

3. Results

Positive. Package exhibits ultrasonic whistling sound, indicating a leak is present, permitting air to enter or exit package.

Negative. No sound is emitted by package within range of frequencies monitored.

False positive. Background noise occurred within range monitored.

False negative. Hole does not emit a noise within the range monitored, or hole was occluded by moisture or food.

Echo. The objective is to actively sense the frequency of echoes in hermetically sealed containers. When a package possessing a vacuum is tapped, the tightness of the package creates a sound that is audibly different from that of the same package without a vacuum. Two changes can be monitored: frequency and amplitude. Changes in frequency (vibrations per second) are recognized as differences in tone (pitch). Changes in amplitude are recognized as 2 relative difference in volume. Loss of hermetic integrity will result in microbial growth within the contents of a food package during incubation. Changes in sound accompany changes in viscosity. Consequently, this method may be used as a nondestructive test for a number of product/package combinations.

1. Materials
• Control sample
• Samples to be evaluated
• Tapping device (electronic device or unsharpened pencil to be used like a drumstick)
• Incubator

2. Procedure

Obtain sample packages, either newly packed or incubated, and a control package (known to be properly sealed) containing the same product as sample packages. Tap the section of the package covering that is taut. Listen to the echo for differences between packages. Commercial devices are available that electronically monitor the echos, allowing for a less subjective determination.

3. Results

Positive. Package displays audibly different sound, indicating loss of hermetic integrity.

Negative. Package resonates at same frequency as control package.

False positive. Differences in vacuum level or fill volume create different sounds in test packages.

False negative. Audible difference between control package and test package cannot be differentiated.

17. Tensile strength (Arndt, 1990)

The objective is to measure the tensile strength required to cause separation of peelable or fused seals. A section of a seal is obtained by cutting a 1/2 or 1 inch (1.3-2.5 cm) strip perpendicular to the seal edge. The strip is then clamped by opposing grippers and pulled at constant speed and defined angle until failure is obtained. The peak force required to fully separate the 2 halves is recorded as the strength of the seal.

1. Materials
• Sample packages
• Sample cutting apparatus
• Scissors (sample dimensions are critical to precision)
• Tensile strength testing device

2. Procedure. See ASTM D-882 - Standard test methods for tensile properties of thin plastic sheeting (ASTM, 1985).

Remove representative sample from production line. Cut open sample and remove contents. Do not disturb seal to be tested. Cut a segment of the seal to produce a test strip. Test strip must be cut perpendicular to the seal to be tested. Secure both ends of test strip in separate clamps. With screwdriver, move one screw clamp away from the other, creating a 180E separation of the seal. Observe force required to fully separate seal. Fixtures are required to hold samples at angles different from 180º.

3. Results

Positive. Sample separates at peak tensile strength less than established standard.

Negative. Sample separates uniformly at peak tensile strength greater than or equal to established standard.

False positive. Sample separates at peak tensile strength less than established standard because of equipment miscalibration or greater separation speed of jaws.

False negative. Sample separates at tensile strength greater than or equal to established standard. However, a different portion of the same sample failed at a tensile strength less than the standard.

18. Vacuum testing (Arndt, 1990)

The objective is to cause the movement of air out of a sealed container through leaks by using external vacuum within a testing chamber. Closed packages are placed inside a sealed testing chamber and vacuum is created to cause movement of air through leaks in the packages. Deflection of the package may be measured as a function of time to determine whether leakage has occurred. If vacuum chamber contains water, bubbles from holes in packages may be observed.

1. Materials
• Bell jar (glass or plastic) with tight-fitting lid
• Water to cover package within bell jar
• Weighted fixture to keep package below water level during test
• Vacuum pump
• Vacuum gauge
• Valve Grease for tight gasketing of lid on chamber

2. Procedure

Obtain representative sample from production line. Place one sample inside vacuum chamber. Evacuate chamber. Observe package swelling and any movement of air (bubbles) or product through holes that may be present or may have developed. When vacuum is released, observe packages to determine if original shape is retained or if atmospheric pressure causes sample to appear slightly crushed.

3. Results

Positive. Leak in test package causes air or product to escape through holes in container. Container ruptures or lid separates because of weak closure. When vacuum is released, package appears distorted or crushed by atmospheric pressure.

Negative. Package distorts under vacuum but no loss of product or air is observed. When vacuum is released, package assumes its original configuration.

False positive. Air clinging to surface of package or within paper laminates is mistaken for bubbles emitting from a defect.

False negative. Food particles prevent movement of air out of a hole in container while under vacuum.

19. Visual inspection (Arndt, 1990)

The objective is to visually observe defects in food packages. Representative samples are obtained from production line. External surfaces are examined for holes, abrasions, delamination, and correct design. Critical dimensions are measured and observations recorded.

1. Materials

Strong light without glare, for visual inspection of packages Measuring devices, such as ruler, calipers, micrometer Scissors or knife

2. Procedure

Refer to examination procedures for paperboard packages, flexible pouches, plastic packages with heat-sealed lids, and plastic cans with double-seamed metal ends.

3. Results

Positive. Visually detected defect.

Negative. No visually detected defects.

False positive. Visual identification of defect not actually present.

False negative. Defect is present, but not visually detected.

Contents

Container Integrity Glossary (Lin et al., 1998)

BASE PLATE PRESSURE- Force of the base plate that holds the can body and end against the chuck during the double seaming operation. In general, it has the following effect on the seam formation: low pressure, short body hook; high pressure, long body hook.

BODY- The principal part of a container, usually the largest part in one piece comprising the sides. The body may be cylindrical, rectangular, or another shape.

BODY HOOK- The flange of the can body that is turned down in the formation of the double seam.

BOTTOM SEAM- Double seam of the can end put on by the can manufacturer, also known as factory end seam.

CABLE CUTS- Cuts or grooves worn into can ends and bodies by cables of the runway conveyor system.

CAN, SANITARY- Full open-top 2-piece drawn can and 3-piece can with double seamed bottom. Cover or top end is attached with a double seam by the packer after filling. Ends are compound-lined. Also known as packer's can or open-top can.

CANNER'S END- See Packer's end.

CAP TILT- Cap should be essentially level with transfer bead or shoulder.

CHIPPED GLASS FINISH- Defect in which a piece of glass has broken away (chipped) from the finish surface.

CHUCK- Part of a closing machine that fits inside the end countersink and acts as an anvil to support the cover and body against the pressure of the seaming rolls.

CHUCK WALL- Part of the can end that comes in contact with the seaming chuck (Figure 5-40).

COCKED CAP- Cap not level because cap lug is not properly seated under glass lug.

CODE CUT- Fracture in the metal of a can end caused by improper code embossing.

COLD WELD- Weld appears narrower and lighter than normal and may be scalloped. Fails the pull test, possibly exhibiting a zipper or sawtooth type of failure.

CONTAMINATION IN WELD AREA- Any visible burn at one or more points along side seam.

COMPOUND- Sealing material consisting of a water or solvent dispersion or solution of rubber and placed in the curl of the can end. The compound aids in producing a hermetic seal by filling spaces or voids in the double seam

COUNTERSINK DEPTH- Measurement from top edge of double seam to end panel adjacent to chuck wall.

COVER- See Packer's end.

COVER HOOK- The part of the double seam formed from the curl of the can end. Wrinkling and other visual defects can be observed by stripping off the cover hook.

CRACKED GLASS FINISH- Actual break in the glass over the sealing surface of the finish. Also known as split finish.

CRAWLED LAPS- Occurs when two layers of metal are bent and the outer layer looks shorter because it has a greater radius to traverse than the inner layer, which has a smaller radius, perhaps being bent almost double. Also known as creep.

CROSS-OVER- The portion of a double seam at the juncture with the side seam of the body.

CROSS-SECTION- A section cut through the double seam for the purpose of evaluating the seam.

CRUSHED LUG- Lug on cap forced over glass lug, causing the cap lug not to seat under glass lug.

CURL- Extreme edge of the cover that is turned inward after the end is formed. In metal can double seaming, the curl forms the cover hook of the double seam. For the closure for glass containers, the curl is the rolled portion of metal at the bottom of the closure skirt (may be inward or outward).

CUTOVER- A break in the metal at top of inside portion of double seam caused by a portion of the cover being forced over the top of the seaming chuck. This condition usually occurs at the cross-over. Also known as a cut through by some can manufacturers. These manufacturers refer to a cutover as the same condition without the break.

CUT THROUGH- Gasket damage caused by excessive vertical pressure.

DEADHEAD- An incomplete double seam resulting from the seaming chuck spinning in the end's countersink during the double seaming operation. Also known as a spinner, skidder, or slip.

DELAMINATION- Any separation of plies (laminate materials) that results in questionable pouch integrity.

DOUBLE SEAM- Closure formed by interlocking and compressing the curl of the end and the flange of the can body. It is commonly produced in 2 operations. The first operation roll preforms the metal to produce the 5 thicknesses or folds; the second presses and flattens them together to produce double seam tightness.

DROOP- Smooth projection of the double seam outside and below the bottom of the normal seam. Usually occurs at the side seam lap area.

FACTORY END- See Manufacturer's end.

FALSE SEAM- Double seam where a portion of the cover hook and body hook are not interlocked, i.e., no hooking of body and cover hooks.

FINISH- That part of the glass container for holding the cap or closures.

FLANGE- Outward flared edge of the can body cylinder that becomes the body hook in the double seaming operation. For weld cans, any flange crack at or immediately adjacent to the weld is a major defect.

FLEXIBLE CONTAINER- A container, the shape or contour of which, when filled and sealed, is affected by the enclosed product.

HEAVY LAP- A lap containing excess solder. Also called a thick lap.

HOOK, BODY- See Body hook.

HOOK, COVER- See Cover hook.

IMPROPER POUCH SEAL- A defect (e.g., entrapped food, grease, moisture, voids, or fold-over wrinkles) in that area of the closure seal that extends 1/8 inch (0.3 cm) vertically from edge of seal on food product side and along full length of seal.

IRREGULAR WELD WIDTH- Any obvious irregularity in weld width along length of side seam.

JUMPED SEAM- See Jumpover.

JUMPOVER- Double seam that is not rolled tight enough adjacent to the cross-over; caused by jumping of the seaming rolls at the lap.

JUNCTURE- The junction of the body side seam and the end double seam, or that point where the 2 seams come together. Also known as the cross-over.

KNOCKED-DOWN FLANGE- Common term for a false seam where the bottom of the flange is visible below the double seam. A portion of the body flange is bent back against the body without being engaged with the cover hook.

LAP- The section at the end of the side seam consisting of 2 layers of metal bonded together. As the term implies, the 2 portions of the side seam are lapped together to allow for the double seam, rather than hooked, as in the center of the side seam.

LID- See Packer's end.

LIP- Projection where the cover hook metal protrudes below the double seam in one or more "V" shapes. Also known as a vee.

LUG CAP- Closure with raised internal impressions that intermesh with identical threads on the finish of the glass container. It is a closure with horizontal protrusions that seat under angled threads on the glass container finish.

MANUFACTURER'S END- End of the can that is attached by the can manufacturer.

NOTCH- Small cut-out section in the lap designed to facilitate the formation or the body hook at cross-over.

OPEN LAP- A lap that is not properly soldered or has failed by separating or opening because of various strains in the solder.

OVERLAP- Distance the cover hook laps over the body hook. Any observable loss of overlap along the side seam is a critical defect.

PACKER'S END- End of the can attached and coded by the food packer. Also known as the canner's end.

PLATE- General term for tinplate, aluminum, and the steel sheets from which cans are made. It is usually tin plate, which is black plate with tin applied to it.

PRESSURE RIDGE- Impression (chuck impression) around the inside of the can body directly opposite the double seam.

PULL-UP- Term applied to distance measured from the leading edge of the closure lug to the vertical neck ring seam.

SAWTOOTH- Partial separation of the weld side seam overlap at one or more points along the seam. If observed after performing the pull test, it is considered a critical defect.

SEAM NARROWING- A steadily visible narrowing of the weld at either end of the weld side seam is a critical defect.

SEAM THICKNESS- Maximum dimension of double seam measured across or perpendicular to layers of seam.

SEAM WIDTH (LENGTH OR HEIGHT)- Maximum dimension of double seam measured parallel to folds of seam.

SECURITY- Residual clamping force remaining in the closure application when gasket has properly seated after processing and cooling.

SEMIRIGID CONTAINER- A container, the shape or contour of which, when filled and sealed, is not affected by the enclosed product under normal atmospheric temperature and pressure, but which may be deformed by external mechanical pressure of less than 10 psi (69 kPa) (i.e., normal firm finger pressure).

SIDE SEAM- The seam joining the 2 edges of the body blank to form a can body.

SKIDDER- Can with incompletely finished double seam because the can slipped in the seaming chuck. In this defect, part of the seam will be incompletely rolled out. The term has the same meaning as deadhead when referring to seamers that revolve the can. Also known as a spinner.

SOFT CRAB- Colloquial term used to describe a breakdown in the packer's can resulting in a hole between end and body.

SPINNER- See deadhead and skidder.

STRIPPED CAP- Lug closure applied with too much torque, which causes lugs to pass over glass lugs. May have vacuum but has no security value.

TIGHTNESS- Degree to which the double seam is compressed by the second operation roll. Tightness is determined primarily by the degree of freedom from wrinkles in the cover hook. Tightness rating is a percentage that ranges from 100 to 0, depending on the depth of the wrinkle: 100% indicates no wrinkle and 0% indicates a wrinkle extending completely down the face of the cover hook. A well-defined continuous impression around the circumference of the can in the double seam area indicates a tight seam. This impression is known as a pressure ridge.

TOP SEAM- Top of packer's end seam.

UNEVEN HOOK- Body or cover hook that is not uniform in length.

WELD CRACK- Class I corrosion products plus any observable seam crack, and any cracks that extend 25% or more across the width of the weld at any point along the weld seam are considered critical defects.

WELD PROTRUSION- Protrusion of the weld in excess of 1/16 inch (0.2 cm) beyond the leading or trailing edge of the can body.

WRINKLE (COVER HOOK)- A waviness occurring in the cover hook from which the degree of double seam tightness is determined.

ZIPPER- Gross separation of the side seam overlap along all or any part of the side seam. If observed during pull test, it is a critical defect.

Contents

Other Analytical Procedures

• Evaluating can double seams (FPI, 1989)
• Flexible package integrity (NFPA, 1989)
• Container evaluation (Gavin and Weddig, 1995)
• Performance of food cans (Hotchner, 1995)
• Guidelines for evaluation and disposition of damaged canned food containers (NFPA, 1998)

Contents

Pasteurizing Processes

Examples of seafood processes are provided for information only. The National Seafood HACCP Alliance does not endorse or recommend specific seafood processes. Some of the referenced processes are of historical interest and may not reflect current best management practices. Processes should not be followed as written without validation.

Blue Crab (Callinectes sapidus) I

Cook crabs for 10 min at 121.1ºC (250ºF) (15 psi, 103.4 kPa) Cool in the retort basket using air circulation or mechanical refrigeration. Refrigerate crab at temperatures below 4.4ºC (40ºF) if delays between cooking and picking occur. Pick crabmeat into 401 flat cans and seal the containers. The crabmeat should be about 26.7-18.3ºC (60-65ºF) when the containers are sealed. Pasteurize within 24 h following picking. Pasteurize containers of crab in a water bath until the geometric center of the containers reach at least 85ºC (185ºF) for at least 1 min. Process 401 flat cans in an 87.8-88.9ºC (190-192ºF) water bath for 110-115 min to give a min. Cool containers in an ice bath at a temperature below 7.2ºC (45ºF) until the temperature of the containers reaches 37.8ºC (100ºF) (about 45 min). Transfer containers to dry storage at 0-2.2ºC (32-36ºF) (Tatro, 1970; Rippen and Hackney, 1992).

Blue crab (Callinectes sapidus) II

Cook crabs as soon as possible after they are delivered to the plant. Refrigerate crabs not cooked within about 2-4 h after delivery at 4.4-10ºC (40-50ºF). Cool crabs in the same container in which they were cooked. If crabs are not picked within about 8 h after cooking, refrigerate them at 4.4ºC (40ºF) or below. Pasteurize within 36 h after picking. Pasteurize to achieve a thermal process of of at least 31 min (Table 5-14). Chill containers to about 12.8ºC (55ºF) or below within 180 min after pasteurization. Cool the containers further to reach 3.3ºC (38ºF) or colder within about 18 h (Rippen et al., 1993).

Table 5-14. F-values achieved for pasteurized blue crab¹.

Heating Time (min)	(min)	Heating Time (min)	(min)
90	5.0	125	35.6
95	6.8	127.5	40.7
100	9.7	130	43.6
105	13.4	132.5	46.5
110	17.3	135	49.4
112.5	21.0	137.5	52.0
115	23.4	140	55.1
117.5	26.8	142.5	58.0
120	30.2	145	60.9
122.5	32.7

¹86.1-87.8ºC (187-190ºF) water bath, 401 ´ 301 cans, crabmeat initial temperature of 15.6-18.3ºC (60-65ºF) (For illustrative purposes only--each pasteurization system must be evaluated independently!) (Rippen et al., 1993).

Blue crab (Callinectes sapidus) III

Cook crabs within 1-2 h after receipt or refrigerate at 7.2-10ºC (45-50ºF). Cook crabs under steam pressure of 15 psig (103.4 kPa) (121.1ºC [250ºF]) for 10 min until the internal temperature of the centermost crab reaches 115.6ºC (240ºF). Air cool crabs to room temperature in the same container in which they were cooked. If not picked within 12 h, refrigerate crabs at 1.7-4.4ºC (35-40ºF). Pick crabmeat into 401 flat cans and seal within 1 h after picking. Pasteurize in a water bath at 87.8-88.9ºC (190-192ºF) for 110-115 min (an internal temperature of 85ºC (185ºF) for 3 min). Cool containers in ice water to an internal can temperature of 32.2ºC (90ºF) (45 min). Transfer to dry storage at 3.3ºC (38ºF) or below (Duersch et al., 1981).

Caviar

Remove sturgeon roe by splitting the belly. Rub roe carefully through a 4-mesh screen over a tub. After collecting all eggs, sift about 1 pound (454 g) of Luneberg salt (or ½ pound (227 g) American dairy salt) over each 12 pounds (5.4 kg) of roe. Mix for 5-8 min and then let stand for about 10 min. Pour roe into sieves with a capacity of 8-10 pounds (3.6-4.5 kg) of caviar and drain for about 1 h. Pack into jars, seal and pasteurize in a hot-water bath at 68.3-71.1ºC (155-160° F) for 30, 45, or 60 min for 1, 2, and 4 ounce (30, 59, and 118 ml) containers (Long et al., 1982).

Dungeness crab (Cancer magister)

Dungeness crabmeat pasteurization processes (Table 5-15) are based on an initial crabmeat temperature of 1.1ºC (34ºF) and do not include the "come-up" time for product to reach process temperature. The processes are 7-D pasteurization processes (Peterson et al., 1997).

Table 5-15. Pasteurization time-temperature intervals and F values for the destruction of nonproteolytic C. botulinum type B spores in Dungeness crabmeat (Peterson et al., 1997).

Process Temp.		Process Time (min)	D value	(min)
(ºF)	(ºC)
192	88.9	90	12.9	247
193	89.4	77.6	11.1
194	90.0	66.8	9.5
195	90.6	57.6	8.2	243
196	91.1	49.6	7.1
197	91.7	42.8	6.1
198	92.2	36.9	5.3	240
199	92.8	31.8	4.5
200	93.3	27.4	3.9
201	93.9	23.6	3.4
202	94.4	20.3	2.9	235

Grain caviar (Russia)

Split open sturgeon belly and remove roe. Rub roe through a metal sieve that has a mesh large enough to permit the eggs to pass through without breaking, but will retain membranes. Mix eggs with salt and place in a sieve as soon as the salt is dissolved. Pack immediately into 9 ounce (255 ml) enameled cans. Process cans for 90 min at 60-65 °C (140-149 °F). Cool for 5 min to 20-30 °C (68-86 °F) with a water spray. Hold for 24 h at 24 °C (73 °F). Repeat pasteurization for a second and third time. Wash and dry cans. Store at 10 °C (50 °F) or less (Jarvis, 1987).

Surimi-based imitation flaked crabmeat

Flaked artificial crab was vacuum-packed into 907 g (2 pound) packages and pasteurized for 25 min in a 91ºC (195.8ºF) water bath to achieve an internal temperature of 81-85ºC (177.8-185ºF) for at least 5 min (Hollingworth et al., 1990).

Smoked salmon

Frozen and eviscerated chum salmon (Oncorhynchus keta) were cut into 1 inch (2.5 cm) thick steaks with an average weight of 180-220 g. The steaks were thawed in plastic bags in cold running water at less than 15.5ºC (60ºF). Steaks were brined in 1.0 to 3.0% salt at 3.3ºC (38ºF) for 3 d with a fish-to-brine ratio of 1 to 7 (weight/volume), rinsed with cold water, and then stored at 3.3ºC (38ºF) in plastic bags for 2 d before smoking. Salmon steaks were smoked at an initial temperature of 60ºC (140ºF) which was increased in 5.6ºC (10ºF) at 30 min intervals. When the steaks reached an internal temperature of 63ºC (145ºF), the smoker temperature was adjusted to maintain the steaks at a constant temperature for at least 30 min. Smoked steaks were cooled and refrigerated overnight, inoculated with 106 spores of C. botulinum types B and E, and vacuum packaged under 23-25 inches (58.4-63.5 cm) vacuum in polyester film bags (O₂ transmission rate of 108 cm³ per M² during 24 h at 22.8ºC (73ºF); CO₂ transmission rate of 526 cm³ per M² during 24 h at 22.8ºC [73ºF])

Packages of smoked salmon were precooled to a uniform internal temperature of 1.1ºC (34ºF) in slush ice. Products were pasteurized in water baths. Pasteurization processes include "come-up" time and are given in Table 5-16. All processes prevented toxin formation by types B and E.

During cooling in slush ice following pasteurization, product internal temperatures dropped below 71.1ºC (160ºF) within 3 min and below 25ºC (77ºF) within 11 min (Eklund, et al., 1988; Pelroy et al., 1982).

Table 5-16. Pasteurization processes for vacuum packaged smoked salmon (Eklund et al., 1988).
 

Processing Temperature		Process Time (min)
(ºF)	(ºC)
185	85	175
192	88.9	85
198	92.2	65

Contents

References

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