Chapter 3: Cooked Fish and Fishery Products

Updated: 9/21/00

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Potential Food Safety Hazard

Pathogen survival through a cook step can cause consumer illness. Cooking is a relatively severe heat treatment, usually performed before the product is placed in the finished product container. Cooking procedures are often established to develop the desirable sensory attributes characteristic of cooked fish and fishery products, not specifically to eliminate pathogens. An important consequence of thorough cooking is the destruction of vegetative cells of pathogens (or reduction to an acceptable level) that may have been introduced in the process by the raw materials or by processing that occurs before the cook step. Cooking processes are not usually designed to eliminate spores of pathogens (FDA, 1998; Rippen 1998).

Undercooking may allow the survival of pathogens leading to several unintentional but potentially hazardous conditions: 1) direct contamination of a ready-to-eat product with pathogens, 2) elimination of other less heat resistant microorganisms that, if present, may suppress pathogen growth or cause spoilage prior to significant pathogen growth, and 3) thermal conditioning of pathogens and increasing their heat resistance to any subsequent cooking or reheating step. It is also possible for a sublethal heating step to trigger bacterial spores to germinate, producing vegetative cells that are more hazardous than spores, but also far more vulnerable to subsequent reheating (Rippen, 1998).

This section on killing pathogens by cooking excludes fish and fishery products processed by pasteurizing (covered in Chapter 5), retorting (covered by the low acid canned foods regulations, 21 CFR 113), smoking (covered in Chapter 7), acidified shelf stable fish and fishery products (covered by the acidified foods regulations, 21 CFR 114), and acidified refrigerated fish and fishery products (covered in Chapter 1).

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Control Measures

Generally, after cooking, fishery products are referred to as cooked, ready-to-eat. Examples of cooked, ready-to-eat products are: crabmeat, lobster meat, crayfish meat, cooked shrimp, surimi-based analog products, seafood salads, and hot-smoked fish.

Controlling pathogen survival through the cook step is accomplished by:

A thorough hazard analysis is important when evaluating a thermal process. In some cases, a cooking or heating step will not present a potential health hazard even if it is sublethal to pathogens. Examples include a blanching step to inactivate enzymes and a par-fry operation to set the breading on products to be fully cooked by the consumer (Rippen, 1998).

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FDA Guidelines

FDA’s recommendations for cooking fish and fishery products to destroy organisms of public health concern in food service, retail food stores, and food vending operations include: FDA guidelines for cooling cooked fish and fishery products:

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State Guidelines

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North Carolina

The North Carolina Administrative Code requires the following: Cook crabs under steam pressure until the internal temperature of the center-most crab reaches 112.8ºC (235ºF). Cook other crustaceans (lobster, shrimp, or crayfish) until the internal temperature of the center-most crustacean reaches 83ºC (180ºF) and is held at this temperature for 1 min. Other cooking processes found equally effective are also allowed (North Carolina, 1997).

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Process Establishment

The adequacy of the cooking process should be established by a scientific study. It should be designed to ensure an appropriate reduction in the numbers of pathogens of public health concern. Selecting the target organism is critical. In most cases it will be a relatively heat tolerant vegetative pathogen, such as Listeria monocytogenes. In some cases, outgrowth of spore-forming pathogens, such as C. perfringens and Bacillus cereus during the post-cook cooling step must be prevented by eliminating these pathogens during the cook. In these cases, the spore-forming pathogens will be the target organisms.

Expert knowledge of thermal process calculations and the dynamics of heat transfer in processing equipment is required to establish such a cooking process. Education or experience, or both can provide such knowledge.

Establishing cooking processes requires access to suitable facilities and the application of recognized methods. The cooking equipment should be designed, operated, and maintained to deliver the established process to every unit of product. In some cases, thermal death time, heat penetration, temperature distribution, and inoculated pack studies will be required to establish the minimum process. In many cases, establishing the minimum process may be simplified by repetitively determining the process needed to reach an internal product temperature that will assure the inactivation of all vegetative pathogens of public health concern (e.g., 82.2ºC [180°F]) under the most difficult heating conditions likely to be encountered during processing. In other instances, existing literature or federal, state, or local regulations establish minimum processes or adequacy of equipment. Characteristics of the process, product, and/or equipment that affect the ability of the established minimum cooking process should be taken into consideration in the establishment of the process. A record of process establishment should be maintained (FDA, 1998).

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D-value

Basing the adequacy of a cooking process on product endpoint temperature is convenient for verification purposes and may be the only alternative for some cooked fish and fishery products. However, microbial lethality is a function of time and temperature, and cooking processed should be based on time and temperature.

Death of bacteria subjected to moist heat is logarithmic. A D-value (decimal reduction time) is the time required to kill 90% of the spores or vegetative cells of a given microorganism at a specific temperature in a specific medium. A 90% reduction in bacteria is equivalent to a reduction from 10,000 bacteria/g to 1,000 bacteria/g or 1 log cycle.

D-values can be determined from survivor curves when the log of population is plotted against time ( Figure 3-1), or by the formula:

Where T = time of heating, a = the initial number of microbial cells, and b = the number of surviving microbial cells after heating time T (Stumbo, 1965; Rippen et al., 1993).

For example, if a suspension containing 10,000 microbial cells/ml is heated for 4 min at 140ºF (60ºC) and only 293 microbial cells survive:

Harrison and Huang (1990) determined D-values for L. monocytogenes (Scott A) in crabmeat (Table 3-2).

Table 3-2. D-values for L. monocytogenes (Scott A) in blue crabmeat.
Temperature
D-value
(ºC)
(ºF)
(min)
50
122
 40.43
55
131
 12
60
140
 2.61

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Z-value

The z-value is the number of ºF or ºC required for a thermal death time curve to traverse 1 log cycle. The z-value gives an indication of the relative impact of different temperatures on a microorganism, with smaller values indicating greater sensitivity to increasing heat. The z-value is obtained by plotting the logarithms of at least 2 D-values against temperature ( Figure 3-2) or by the formula:

Where T 1 and T2 are temperatures and D1 and D2 are D-values at temperatures T1 and T2 (Rippen et al., 1993).

For example, using the D values (D122ºF = 40.43 min and D140ºF = 2.61 min) for L. monocytogenes:

z = 15.1ºF

Z-values are used to determine D-values at different temperatures using the formula:

Where:
D1 = Known D-value at temperature T1
D2 = Unknown D-value at temperature T2

Using the known D-values for L. monocytogenes (Scott A) in blue crabmeat and the z-value, D-values can be calculated for any given temperature. For example, substituting D and z values for Listeria in blue crabmeat (D140 = 2.61 min, z = 15.1ºF) from the Harrison and Huang (1990) study, the equivalent D-value at 185ºF is 0.16 s.

D185 = 0.0027 min or 0.16 s

D-values vary with product type and pubished D-values are rarely determined at the temperatures encountered during commercial processing.. Equivalent D-values should not be calculated for temperatures far hotter or cooler than those used in the original laboratory studies or errors may result due to the non-linerarity of some survivor curves (Rippen, 1998).

Adequate cooking processes are generally 6-D to 7-D processes at the geometric center of the thickest product or container being processed. Table 3.3 gives 1D-, 6-D, and 7-D-values for L. monocytogenes (Scott A) calculated from the Harrison and Huang (1990) study with blue crabmeat.

All cooking processes are product and equipment specific and must be evaluated independently. Any changes in the critical aspects of processes will effect the adequacy of the cook.

Conducting an in-plant process establishment study may result in a lower temperature process resulting in improved quality or yields. A process authority can usually identify alternative cook schedules that achieve equivalent pathogen kill (Rippen, 1998).

Table 3-3. 1-D and 7-D values for L. monocytogenes (Scott A) in blue crabmeat.
Temperature
1-D
6-D
7-D
(ºC)
(ºF)
(Min.)
(Sec.)
(Min.)
(Sec.)
(Min.)
(Sec.)
60 140 2 37 15 40 18 16
60.56 141 2 14 13 27 15 41
61.11 142 1 55 11 33 13 28
61.67 143 1 39 9 55 11 34
62.22 144 1 25 8 31 9 56
62.78 145 1 13 7 19 8 32
63.33 146 1 3 6 17 7 20
63.89 147 - 54 5 24 6 18
64.44 148 - 46 4 38 5 24
65.00 149 - 40 3 59 4 38
65.56 150 - 34 3 25 3 59
66.11 151 - 29 2 56 3 25
66.67 152 - 25 2 31 2 56
67.22 153 - 22 2 10 2 31
67.78 154 - 19 1 51 2 10
68.33 155 - 16 1 36 1 52
68.89 156 - 14 1 22 1 36
69.44 157 - 12 1 11 1 22
70.00 158 - 10 1 1 1 11
70.56 159 - 9 - 52 1 1
71.11 160 - 7 - 45 - 52
71.67 161 - 6 - 38 - 45
72.22 162 - 5 - 33 - 38
72.78 163 - 5 - 28 - 33
73.33 164 - 4 - 24 - 28
73.89 165 - 3 - 21 - 24
74.44 166 - 3 - 18 - 21
75.00 167 - 3 - 15 - 18
75.56 168 - 2 - 13 - 15
76.11 169 - 2 - 11 - 13
76.67 170 - 2 - 10 - 11
77.22 171 - 1 - 8 - 10
77.78 172 - 1 - 7 - 8
78.33 173 - 1 - 6 - 7
78.89 174 -
<1
 - 5 - 6
79.44 175 -
<1
 - 5 - 5
80.00 176 -
<1
 - 4 - 5
80.56 177 -
<1
 - 3 - 4
81.11 178 -
<0.5
 - 3 - 3
81.67 179 -
<0.5
 - 2 - 3
82.22 180 -
<0.5
 - 2 - 2
82.78 181 -
<0.5
 - 2 - 2
83.33 182 -
<0.5
 - 2 - 2
83.89 183 -
<0.5
 - 1 - 2
84.44 184 -
<0.5
 - 1 - 1
85.00 185 -
<0.5
 - 1 - 1
85.56 186 -
<0.5
 - 1 - 1
86.11 187 -
<0.5
 - 1 - 1
86.67 188 -
<0.5
 - 1 - 1
87.22 189 -
<0.1
 - 1 - 1
87.78 190 -
<0.1
 - <0.5 - 1
88.33 191 -
<0.1
 - <0.5 - <0.5
88.89 192 -
<0.1
 - <0.5 - <0.5
89.44 193 -
<0.05
 - <0.5 - <0.5
90.00 194 -
<0.05
 - <0.5 - <0.5
90.56 195 -
<0.05
 - <0.5 - <0.5
91.11 196 -
<0.05
 - <0.5 - <0.5
91.67 197 -
<0.05
 - <0.5 - <0.5
92.22 198 -
<0.05
 - <0.5 - <0.5
92.78 199 -
<0.05
 - <0.5 - <0.5

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F-value

F-value is a numeric way to express the amount of heat received by bacteria at a reference temperature. Stated differently, F-value is the equivalent time spent at a given temperature in terms of microbial kill. F-values allow the direct comparison of two or more processes. For example, testing may show that the same F-value (e.g., F185 = 10 min) is accomplished by heating containers of product for either 1 h at 195ºF or for 2 h at 185ºF: both providing the same effective kill that would be achieved by instantly heating the product to 185ºF, holding for 10 min, then instantly cooling the product. F-values include the lethal heat the product receives during the heating and cooling portion of the process.

F-values and D-values are related in that a process F-value usually represents multiple D-values. If a research study determined that an organism’s D-value was 1 min at 185ºF (D185 = 1 min), then a process with a F185 = 10 min would achieve 10 decimal reductions for the target microorganism, or a 99.99999999 % kill (Rippen, 1998).

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Critical Aspects of Processes

Critical aspects of cooking processes may include:

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Analytical Procedures

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Thermometer calibration

See Chapter 2.

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Determining the adequacy of cooking processes for crawfish: Gelatin test (Moody, 1999)

Theory

Adequate cooking of crawfish eliminates proteolytic enzymes. Gelatin liquefaction is used to indicate the presence of proteolytic enzymes in crawfish after cooking.

Equipment and materials

  1. 12% gelatin solution (by weight, 12 parts gelatin to 88 parts water)
    1. Approximately 1 ounce (28 g) gelatin (four ¼ ounce (7 g) envelopes) to 7 ounces (7/8 cup, 207 ml) water
    2. Bring the solution to a boil to dissolve gelatin
    3. IMPORTANT: cool to about 100ºF (37.8ºC) before using; otherwise the gelatin will "cook" any active enzymes that may be present.
  2. Crawfish fat removed from crawfish samples at 1 min intervals (more or less frequently according to needs) during cooking process
    1. Random sampling is important (i.e., stir crawfish before removing some for test; don’t select crawfish that are all the same size).
    2. Put crawfish in/on labeled containers to avoid confusing crawfish samples removed at different times.
    3. Allow crawfish to cool and remove some fat from 3 or 4 crawfish. About ½ teaspoon (5 ml) of fat for each tablespoon (30 ml) of gelatin solution.
  3. Other needed materials include containers and covers for fat-gelatin mixtures, mixing utensils, utensils for preparation of gelatin solution, etc.

Procedure

  1. Put fat samples from each period into separate labeled containers. Put some raw fat in one container( time "0"); leave one container empty.
  2. Add cooled liquid gelatin to all containers, including the empty one.
  3. Mix well – IMPORTANT: do not cross-contaminate samples when mixing as active enzymes may be carried from a sample cooked less to one cooked more.
  4. Cover containers to prevent drying.
  5. Leave mixtures at room temperature for 1-2 h, and at that time…
  6. Record texture of gelatin-fat mixture and of plain gelatin as follows:


    7. 1 = thin liquid
    2 = thick liquid
    3 = soft gel
    4 = firm gel

    Note: gelatin-raw fat mixture should have a texture = 1; plain gelatin should have a texture = 4, and should serve as a reference when checking for lack of enzyme activity

  7. Refrigerate covered containers overnight at approximately 37-40ºF (2.8-4.4ºC). The next day (about 24 h later) check and record texture again (this is important to detect lower levels of active enzymes which will continue to act on gelatin).
  8. IMPORTANT: enzyme activity is indicated in all gelatin mixtures that have texture softer than "4". These active enzymes can degrade the texture of fresh and frozen crawfish meat packed with fat, and produce a product with an unacceptable textural quality.
An adequate cook process is indicated by the first time yielding crawfish that contain fat samples which allow development of a firm ("4") gel of the fat-gelatin mixture, the texture of which is maintained for at least 24 h

For example,
 
Time

(min.)
Texture
0 (raw)
1
1
1
2
1
3
2
4
2
5
3
6
3
7*
4
8
4
9
4

*Minimum cook time required to eliminate enzymes.

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Other Analytical Procedures

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Commercial test products 

Table 3-4. Commercial test products for cooked fish and fishery products.
Test Kit
Analytical Technique
Approx. Total Test Time
Supplier
CHEF Test with Charm LUM-T meter 
[Used to identify undercooked fish]		 Phosphatase measurement 5 min Charm Sciences, Inc. 
36 Franklin St. 
Malden, MA 02148-4120 
Phone: 781/322-1523 
E-mail: charm1@charm.com 
Web: www.charm.com

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Cooking 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.

Cooked Dungeness crab sections I

Remove crab carapace cleanly. Cut the crabs in half. Brush off intestinal content as completely as possible. Wash and rinse the halves in running water or with spray. Cook the crab sections at 100ºC (212ºF) for at least 15 min (Lee and Hilderbrand, 1992).

Cooked Dungeness crab sections II

Butcher live crab by holding the crab by the legs on each side while bringing the belly down shapely on a knife edge. Shake to jar out viscera that cling to the body cavities. Clean off gills and remaining viscera with revolving nylon brush. Cook crab sections in unsalted boiling water for 10-12 min (Babbitt, 1981).

Cooked whole Dungeness crab

For crab planned for fresh sales, cook whole crab in salted boiling water for 20-25 min. Begin timing cook when water returns to a boil after crab have been added. Use 4-5% salt (16-20º salimeter) in the cook water. (Babbitt, 1981).

Cooked whole Dungeness crab

Live male Dungeness crabs, weighing about 2 pounds (907 g) each, were cooked using either a minimal input of steam (less than 212ºF [100ºC]) or an excess input of steam. After a 23 min cooking period, crabs processes with a minimal input of steam had an internal temperature of 60ºC (140ºF); crabs processed with an excess input of steam had an internal temperature of 77.8ºC (172ºF). All parts of crabs cooked with excess steam input were cooked adequately (Barnett and Nelson, 1966).

Cooked lobster I

Heat lobster for a period of time such that the thermal center of the product reaches a temperature adequate to coagulate the protein (FAO, 1978a).

Cooked lobster II

Place lobsters in 1 layer on racks immersed in fresh boiling water. For whole lobster that will be frozen up to 1 month, cook 1 pound (454 g) lobsters 1-2 min and 1½ pound (680 g) lobsters 2-3 min. For lobsters that will be kept in frozen storage for 3 months or longer, cook 1 pound (454 g) lobsters 8-10 min and 1½ pound (680 g) lobsters 12-14 min. After cooking, cool lobsters in clean cold water for about 10 min, drain 5-10 min, and commence freezing within 1 h (Wojtowicz, 1974).

Cooked lobster III

Lobsters (about 1¼ pounds [567 g]) were cooked in boiling water. With lobster 1, temperature changes were monitored from the time the lobster was placed in the boiling water. For lobsters, 2-4, temperature changes were monitored when the pot began to boil a second time (Table 3-1). Thermocouples were inserted into the lobster’s crusher claw by punching a small hole in the top of the claw, and inserted into the lobster’s tail through the first joint in the carapace. The researchers concluded that 12-15 min cooking time was sufficient to kill disease-causing bacteria (Bushway and Bayer, 1996).

Table 3-1. Temperature changes in lobster claw and tail muscle during cooking in boiling water.
Time
Tail temp.
Claw temp.
(min.)
ºC
ºF
ºC
ºF
Lobster #1        
0
 11.9 53 12.7 55
2
 54.9 131 55.4 132
4
 86.4 188 81.7 179
6
 94.2 202 97.4 207
8
 95.9 205 100.5 213
10
 97 207 103.7 219
12
 98.2 209 105.1 221
14
 98.8 210 105.6 222
15
 99.3 211 105.7 222
Lobster #2
        
0
 14.7 59 16.7 68
2
 52.1 126 67.2 153
4
 67.7 154 79.4 175
6
 84.2 184 88.2 191
8
 91.2 196 93.6 201
10
 94.6 202 98.1 209
12
 95.5 204 100.5 213
14
 96.7 206 101.4 215
15
 98.1 209 101.7 215
Lobster #3
        
0
 17.1 63 19.5 67
2
 61.5 143 60.3 141
4
 78.6 174 84.3 184
6
 90.3 194.5 94.9 203
8
 95.5 204 100.0 212
10
 97.4 207 102.2 216
12
 99.6 211 103.1 218
14
 100.4 213 103.4 218
15
 100.8 213 103.4 218
Lobster #4
        
0
 16.6 62 17.1 63
2
 53.3 128 69.1 156
4
 62.9 145 79.9 176
6
 70.5 159 97.4 207
8
 88.7 192 101.5 215
10
 94.4 202 104.4 220
12
 96.7 206 105.7 222
14
 97.8 208 106.1 223
15
 98.5 209 106.2 223

 Cooked Pacific shrimp

Controlled experiments with a pilot scale mechanical peeler gave 23.5% yields for untreated shrimp and 28.6% yields for shrimp treated with 1.5% condensed phosphate for 5 min prior to steam precooking. The shrimp were fed onto a steam pre-cooker no more than 1 body layer thick and cooked for 90 s in steam at 101ºC (213.8ºF) (Crawford, 1980).

Cooked shrimp

Boil shrimp in potable water, clean sea water, or brine or heat in steam for a period of time sufficient for the thermal center of the shrimp to reach a temperature adequate to coagulate the protein (FAO, 1976; FAO, 1978b).

Inactivation of C. botulinum toxin

Cooking to an internal temperature of 79ºC (174.2ºF) for 20 min or to an internal temperature of 85ºC (185ºF) for 5 min inactivates any C. botulinum toxin at concentrations up to 105 LD50/g in foods (Woodburn et al., 1979).

Note: LD50 is an abbreviation for the dose (expressed in milligrams per kilogram of body weight of the test animal) that is lethal to 50 per cent of the group of test animals (Ali, 1995).

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References

Ali, S. (Ed.). 1995. Pesticide toxicity, hazard and risk. http://itsd-s3.agric.gov.ab.ca/pests/pestcide/toxicity.html#LD50 (25 June, 1998).

Babbitt, J.K. 1981. Improving the Quality of Commercially Processed Dungeness Crab. SG 65, Oregon State University, Extension Marine Advisory Program, Corvallis, OR.

Barnett and Nelson, 1966. Recent technological studies of Dungeness crab processing. Part 4 – Preliminary report on salt uptake and heat penetration in whole cooked crab. Fishery Industrial Research 3(3):13-16.

Bushway, A.A. and Bayer, R. 1996. Lobster processing temperature recordings needed for HACCP plans. MSG-E-96-11. Maine/New Hampshire Sea Grant College Program and the Lobster Institute, 5715 Coburn Hall #22, University of Maine, Orono, ME.

Crawford, D.L. 1980. Meat yield and shell removal functions of shrimp processing. Special Report 597, Oregon State University, Extension Marine Advisory Program, Seafoods Laboratory, Astoria, OR.

FAO. 1976. Recommended international standard for quick frozen shrimps and prawns. CAC/RS 92-1976. Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission, Food and Agriculture Organization of the United Nations, World Health Organization, Rome.

FAO. 1978a. Recommended international standard for quick frozen lobsters. CAC/RS 95-1978. Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission, Food and Agriculture Organization of the United Nations, World Health Organization, Rome.

FAO. 1978b. Recommended international code of practice for shrimps and prawns. CAC/RCP 17-1978. Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission, Food and Agriculture Organization of the United Nations, World Health Organization, Rome.

FDA. 1998. Pathogen survival through cooking. Ch. 16. In Fish and Fishery Products Hazards and Controls Guide, 2nd ed., p. 189-196. Department of Health and Human Services, Public Health Service, Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Seafood, Washington, DC.

FDA. 1999a. Destruction of organisms of public health concern: Cooking (raw fish). p. 53. Section 3-401.11(A)(1). 1995. Food Code, United States Public Health Service, Food and Drug Administration, Washington, DC.

FDA. 1999b. Destruction of organisms of public health concern: Cooking (comminuted fish). p. 54. Section 3-401.11(A)(2). 1995. Food Code, United States Public Health Service, Food and Drug Administration, Washington, DC.

FDA. 1999c. Destruction of organisms of public health concern: Cooking (stuffed fish). p. 54. Section 3-401.11(A)(4). 1995. Food Code, United States Public Health Service, Food and Drug Administration, Washington, DC.

Harrison M.A. and Huang, Y. 1990. Thermal death times for Listeria monocytogenes (Scott A) in crabmeat. J. Food Protect. 53:878-880.

Lee, J.S. and Hilderbrand, K.S. 1992. Hazard analysis & critical control point applications to the seafood industry. Oregon Sea Grant Publication ORESU-H-92-001. Oregon State University, Corvallis, OR.

Lind, J. 1965. Determination of activity of acid phosphatase in canned hams. Danish Meat Products Laboratory, The Royal Veterinary and Agriculture College, September 23, 1965.

Moody, M. 1999. The gelatin test. Louisiana State University, Baton Rouge, LA.

North Carolina. 1997. Handling, packing and shipping of crustacea meat. North Carolina Administrative Code, Title 15A, Department of Environment, Health and Natural Resources, Chapter 18, Environmental Health, Subchapter 18A - Sanitation, Section .0100 - (April, 1997).

Rippen, T.E. 1998. Personal communication. University of Maryland, Princess Anne, MD.

Rippen, T.E., Hackney, C.R., Flick, G.J., Knobl, G.M., Ward, D.R., Martin, R.E., and Croonenberghs, R. 1993. Seafood Pasteurization and Minimal Processing Manual. Virginia Cooperative Extension Publication 600-061 (1993), Virginia Sea Grant Publication VSG 93-09, Virginia Polytechnic Institute and State University, Blacksburg, VA. 173 p.

Stumbo, C.R. 1965. Thermobacteriology in Food Processing. Academic Press, New York, NY.

USDA. 1993. Internal cooking temperature determination (ICT1-2). In FSIS Analytical Chemical Laboratory Guidebook. Chemistry Division, Food Safety and Inspection Service, U.S. Department of Agriculture, Washington, DC.

Woodburn, M.J., Somers, E., Rodriguez, J. and Shantz, E.J. 1979. Heat inactivation rates of botulinum toxins A, B, E, and F in some foods and buffers. J. Food Sci. 44: 1658-1661.

Wojtowicz, M.B. 1974. Information on production of whole, frozen lobsters. New Series Circular No. 74. Environment Canada, Fisheries and Marine Service, Halifax Laboratory, Halifax, Nova Scotia.