The market for vacuum-packed pasteurized seafood products is developing rapidly. The stability and safety of pasteurized products rely on pasteurization processes and subsequent storage at refrigeration temperatures. The aim of this work was to study the heat resistance of characteristic bacterial flora responsible for spoilage in pasteurized seafood products and to determine the minimal pasteurizing value required for the destruction of nonsporeforming bacteria. The DT and z-values were determined for various bacteria selected from among the most heat-resistant bacteria isolated from seafood products (Pseudomonas paucimobilis, Pseudomonas putida, Micrococcus varians, Enterococcus faecium and Staphylococcus aureus). Thermal resistance was measured in different media (fish fillet, fish terrine and M/15 phosphate buffer). The most heat-resistant microorganism found was Pseudomonas paucimobilis: the D70 varied between 1.16 and 3.36 min, and the z-value, between 5.8 and 9.1°C, depending upon the medium. The minimal pasteurizing values required to destroy a sufficient proportion of nonsporulated bacteria were determined. In France, the pasteurizing value is designated PTZ. The reference temperature was 70°C (the official reference temperature in France). In fish, the minimal pasteurizing value, p706 = 15 min, should be applied to ensure the destruction of almost any vegetative forms of bacteria. In a fish terrine, the minimal pasteurizing value should be P709 = 30 min.

No abstract

H2S+ bacteria responsible for the degradation of sulfur‐containing amino acids of fish muscle are currently little used to evaluate the microbiological pal quality of fish. Shewanella putrefaciens greatly predominates in this flora, and was therefore used to define a suitable culture method and medium. Inoculations by the Spiral surface method at 25C, with an incubation of 72h, gave the best counts on a medium containing two sources of sulfur (organic and inorganic) for H2S+ bacteria. The culture medium and the NaCl concentration were determinant in the evaluation of this flora. At present there is no standard medium which meets these requirements.

Bacterial reduction of trimethylamine N‐oxide (TMAO) cannot be reliably determined try qualitative methods, which are unusable because of problems relating to incubation time, the indicator and the equilibrium of the redox potential. This makes it difficult to reproduce results. These problems have been observed with various semi‐agar media used in the evaluation of TMAO reduction. We propose a new and rapid method of quantitative evaluation by means of assay of trimethylamine (TMA) in a new TMA‐free culture medium. This methodology has been used to evaluate the TMAO‐reducing capacity of different endogenous and exogenous bacterial strains found in fish flesh (Aeromonas hydrophila, Alteromonas communis, Escherichia coli, Flavobacterium branchiophilum, Micrococcus sedentarius, Proteus mirabilis, Pseudomonas fluorescens, Pseudomonas nautica, Serratia marcescens, Shewanella putrefaciens, Vibrio parahaemolyticus). Unlike the qualitative methods, our method showed that all tested strains were able to reduce TMAO. Fish spoilage bacteria can form TMA under anaerobic conditions, as shown by tests using bacterial suspensions from fish (Helicolenus dactylopterus, Merlangus merlangus, Clupea harengus). Such tests can be used to assess fish spoilage.

H2S bacteria of seafish flesh are weakly halophilic and require on average 1.68% NaCl according to statistical studies. Enumeration is optimal on PCA‐H2S(a PCA medium supplemented with sulfur sources and increased NaCl concentrations) incubated at 25C. Total aerobic bacteria can be counted simultaneously on this medium. The proportion of H2S bacteria relative to total aerobic bacteria increased slightly during prolonged storage of the fish, but was highly variable. Models relating H2S bacterial counts to spoilage of fish are sigmoidal and showed that when the count exceeds 10,000 CFU/g, whole or filleted fish stored in ice at 0C are unfit for consumption. Shewanella putrefaciens accounted for 69% of the H2S bacteria at the fifth day of storage and 100% at the fifteenth.