Fish sauce microbiology

While it is evident that microorganisms are present during the production of fermented fish sauces, it is not clear to what extent these organisms contribute to the finished product. The microbial population in raw, unsalted fish and shellfish is high in number and rich in diversity. Considering the fact that whole unevis-cerated fish (guts and all) are usually used to make fish sauces, the initial load of organisms is significant.

In addition, the manufacturing environment is not aseptic, and even the salt (usually obtained by solar drying of sea water) may contribute microorganisms. However, the high salt concentration established early on in the fermentation provides strong selective pressure for halotolerant organisms. Not surprisingly, therefore, there is a shift in the initial bacterial population, from a wide variety of aerobic and anaerobic organisms to a more narrow microflora consisting mainly of salt-tolerant species of Bacillus, Halobacillus, Staphylococcus, and Micrococcus. Lactic acid bacteria are also widely present in fish sauce (Table 12-10), including some strains that are capable of growing in media containing 12% (2.1 M) salt.

Table 12.10. Lactic acid bacteria isolated from fish i sauces'.

Organism

Lactobacillus plantarum Lactobacillus farciminis Lactobacillus acidipiscis Lactobacillus pentosus Weissella thailandensis Leuconsotoc citreum Lactococcus lactic subsp. lactis Tetragenococcus muriaticus xFrom Tanasupawat et al., 1998,Tanasupawat et al., 2000, Paludan-Muller et al., 1999, and Kimura et al., 2001

Establishing the function of the microflora during the fish sauce fermentation is not easy. It has been suggested that there is a succession that occurs during the fermentation, leading to the eventual dominance of the more salt- and acid-tolerant organisms. While this may be true for some products, in which considerable microbial growth is evident, for other products, microbial growth hardly occurs. In either case, the population eventually decreases, such that at the end of the fermentation (six to twelve months), there are usually less than 103 cells per ml. Many of the organisms isolated from fermented fish products have proteolytic activity and likely contribute, at least in part, to the overall proteolysis of fish protein. Lactic acid bacteria and other anaerobes also can metabolize amino acids, producing volatile fatty acids, amines, ammonia, and other volatile end-products.

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Responses

  • heike
    What organisms contribute to the fermentation of fish sauce?
    2 months ago

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