Evaluation of the effects of a novel ozonised-slurry ice combined system on the microbial quality of comercial fish species

Campos C.A.^a,b, Rodríguez Ó.^a, Losada V. ^c, Aubourg S.P.^c, Veiga P.^a, and Barros-Velázquez J. ^a,*.

^aDepartment of Analytical Chemistry, Nutrition and Food Science, School of Veterinary Sciences, University of Santiago de Compostela, E-27002 Lugo, Spain; ^bDepartment of Industries, School of Exact and Natural Sciences, University of Buenos Aires, Ciudad Universitaria (1428) Buenos Aires, Argentina; and ^cDepartment of Seafood Chemistry, Institute for Marine Research (IIM-CSIC), C/ Eduardo Cabello 6, E-36208 Vigo, Spain. E-mail: jbarros@lugo.usc.es

Aim: A novel ozonised-slurry ice system was developed and evaluated with respect to both slurry ice and traditional flake ice, as a new refrigeration system for the storage of three different commercial fish species.

Methodology: The composition of the slurry ice binary mixture was 40% ice and 60% water, prepared from filtered seawater. The concentration of ozone in the flow ice mixture was 0.17 mg/l. Sensory assessment of the fish included the examination of skin, external odor, gills, consistency and flesh odor. Microbiological analyses included the investigation of both surface and muscle microorganisms, the following microbial groups being considered: total aerobes, psychrotrophic bacteria, anaerobes, coliforms, lipolytic bacteria, proteolytic bacteria, H₂S-producing bacteria and histamine-producing bacteria. Complementary analyses included the investigation of pH, TMA-N and TVB-N. Statistical analyses were considered at the p<0.05 level.

Results: According to sensory analyses, the fish specimens stored in ozonised slurry ice exhibited an extended shelf life as compared with counterpart batches stored in slurry ice or flake ice. Storage in ozonised slurry ice led to significantly (p<0.05) lower counts of aerobic mesophiles, psychrotrophic bacteria, anaerobes, coliforms, and both lipolytic and proteolytic microorganisms in muscle, and of surface counts of mesophiles and psychrotrophic bacteria in skin, as compared with the slurry ice and the flake ice batches. The combination of slurry ice with ozone also allowed a better control of pH and TMA-N formation as compared with slurry ice alone or flake ice, thus indicating a reduction in the microbial activity in such batch.

Conclusion: This work demonstrates that the combined use of slurry ice and ozone for the storage of different fish species is recommended in the seafood industry, to slow down microbial growth thus improving the quality and shelf life of seafood products.