Fish sauce fermentation using Marinococcus halotolerans SPQ isolate as a starter culture

A total of 344 halophilic bacteria were isolated from fish fermentation broths, solar salt crystals, seawater, and muds from ponds of salt pans in Vietnam and subjected to aroma evaluation using fish broth containing 29 ~ 30% (w/v) NaCl. One isolate from a salt crystal with the highest aroma score was selected, identified by using 16S rDNA sequence, and named Marinococcus halotolerans SPQ. The GC-MS results of the fish broth fermented by M. halotolerans SPQ revealed elevated concentrations of several aroma compounds such as ethyl alcohol, 1-propanol, 1-butyl alcohol, 1-amyl alcohol, and methionol. During the validation tests for M. halotolerans SPQ, using 2 kg of anchovy fish in 30% (w/v) NaCl at pH 5.78, the total and amino nitrogen values in the broth increased over time from 15.2 g/L at the beginning to 26.3 g/L at 6th month, with these values being comparable to those of the control. The ammoniacal nitrogen value (2.52 g/L) in the inoculated broth at 6th month was slightly higher than that (2.21 g/L) of control. The histamine content of the fish broth inoculated with M. halotolerans SPQ after 6 months was 110.12 mg/L, less than the maximum permitted safety limit of 200 mg/L, indicating it to be safe. Physical parameters, such as the total, amino, ammoniacal nitrogens, and histamine content of fish broth fermented by M. halotolerans MPQ met the standards for Vietnamese fish sauces. Two important umami amino acids, aspartic and glutamic acid, were seen to significantly increase, by 23.5% and 35.1%, respectively, even in the extremely harsh fermentation conditions posed by 30% (w/v) NaCl. The color, odor, and taste of the fish sauce fermented by M. halotolerans SPQ elicited the highest preference score accorded by the panelists. Taken together, M. halotolerans SPQ is a promising starter culture strain for fish sauce fermentation.