Abstract: We investigated the effects of four strains of Planococcus with protease activity at low temperature (15 ℃) isolated from traditional fermented shrimp paste on the quality of low-salt fish sauce. The strains were screened for their enzymatic activity at 40 ℃. Among these, strain XJ11 showed the highest protease activity of (10.07 ± 0.11) U/mL. Based on morphological observation and 16S rRNA sequence alignment, all four strains were identified as Planococcus and named P. maritimus XJ2, P. plakortidis XJ10, P. dechangensis XJ11 and P. rifietoensis XJ12, respectively. The strains grew well in a low-temperature, low-salt, and alkaline environment. The protease produced by Planococcus exhibited the highest enzymatic activity at 40 ℃ at pH 9.0 and showed good salt tolerance. A 1:1:1:1 mixture of the four strains was inoculated at 3% as a starter culture in low-salt fish sauce fermentation. The results showed that the amino acid nitrogen content of low-salt fish sauce inoculated with the starter culture was (1.33 ± 0.08) g/100 mL, which was significantly higher than that of the control prepared without the starter culture ((0.89 ± 0.02) g/100 mL) (P < 0.01). The amounts of the key desirable volatiles such as alcohols, ketones, acids, esters and pyrazine were higher than in the control. In summary, the starter culture increased the amino acid nitrogen content of low-salt fish sauce and improved the flavor effectively.

Key words: fish sauce; Planococcus; protease; fermentation; low-salt; low-temperature