Selection of bacterial strains for improvement of fish sauce fermentation

By traditional methods employed in fish sauce production, fermentation of fish sauce requires a year. To decrease the time of fermentation, a better understanding of the microbiology of fish sauce is needed. Since the hydrolytic process was considered to be the major point for increasing the rate of fermentation, this study concentrated on proteolytic and lipolytic bacteria. Fish sauce is a lactic fermented product, so the major bacterial groups of interest were the lactic acid bacteria and the volatile substance-producing bacteria found in fish sauce.; At the beginning of the fermentation, a Pseudomonas sp. and Bacillus spp. comprised the predominant nonhalotolerant proteolytic bacteria; however, this group was not detected after one month. During the first two months, Bacillus spp. were the most common halotolerant proteolytic bacteria. The number of halotolerant bacteria sharply increased in the third month, predominantly coagulase negative Staphylococcus, coryneform bacteria, and Micrococcus varians. The major proteolytic, halophilic group included a new species of the genus Halobacillus, Halobacillus thailandensis. Lipolytic bacteria isolated from fish sauce were dominated by coagulase negative Staphylococcus, and Micrococcus spp. Lactic acid bacteria dominant in the fermentation were identified as Pediococcus halophilus. There was an indication of a relationship between number of proteolytic bacteria and concentration of protease in the fermenting liquid.; From the results obtained in this study, it was concluded that Halobacillus thailandensis, Micrococcus varians, and Pediococcus halophilus should be selected for analysis with the objective of accelerating fish sauce fermentation. H. thailandensis produces two extracellular serine-proteases, and one metallo-protease, detected by gelatin-PAGE. These enzymes were present in the fermenting fish sauce.; Pediococcus halophilus is concluded to play an important role in the formation of the characteristic aroma of fish sauce by producing volatile fatty acids at significant concentrations in fish meal hydrolysate, with a volatile fatty acid profile similar to that of fish sauce during production.; In conclusion, fish sauce production, carried out by enhancing hydrolytic activities, notably of the proteolytic and lipolytic bacteria, at an equilibrium that does not disturb fish sauce aroma formation, can be achieved with shorter fermentation times than the traditional method of production.