Improvement of fish-sauce odor by treatment with bacteria isolated from the fish-sauce mush (Moromi) made from frigate mackerel

A bacterium, which was isolated from fish-sauce mush (moromi) of frigate mackerel and identified as Staphylococcus xylosus, could change notes of an odor in fish sauce made in Thailand. Volatile compounds of the fish sauce after incubation at 32 degreesC for 24 d with the cultured bacterium were analyzed by gas chromatography. Although the contents of 2-ethylpyridine and dimethyl trisulfide were reduced during the incubation, 4 volatile compounds, including 2-methylpronal, 2-methylbutanal, 2-pentanone, and 3-(methylthio)propanal, showed no significant quantity changes. On the other hand, although 3-methyl-1-butanol and 2,6-dimethylpyrazine were markedly increased, 3-methylbutanoic acid was slightly increased. As a result of sensory evaluation, fishy, sweaty, fecal, and rancid notes of the fish sauce treated with the bacterium were all weaker than those of the nontreated fish sauce. No changes were found with respect to burnt, cheesy, meaty, and ammoniacal notes between fish sauce treated with the bacterium and that without treatment. Taken together, the odor of fish sauce was much improved by treatment with the isolated bacterium.