Extremely halophilic strains of Halobacterium salinarum as a potential starter culture for fish sauce fermentation

Abstract

Proteinase-producing halophilic archaea were isolated from Thai fish sauce collected from industrial fermentation tanks at various periods of fermentation. Five isolates namely, J-1-S4, J-1-S13, J-1-S22, 2 m-40-15-R2, and P-1-S8, were identified as Halobacterium salinarum with slightly different colony and morphological characteristics among isolates. Starters of five isolates were prepared and added to the anchovy mixed with 25% solar salt and fermented for 180 days at 30–35°C. Halophilic bacteria/archaea counts of inoculated samples were decreased and undetected after 120 days of fermentation. At 180 days of fermentation, α-amino group contents of inoculated fish sauce samples (856–1010 mM) and total nitrogen content (2.2%–2.5%) were higher than the control without archaea inoculation (p < 0.05). All samples contained low amounts of biogenic amines, suggesting that all starters were not biogenic amine formers. The major volatile compound found in samples inoculated with H. salinarum P-1-S8 and H. salinarum 2 m-40-15-R2 was 3-methylbutanal, which contributes to the meaty note. Dimethyl disulfide, a compound that contributes to fecal note, was detected in all inoculated samples in a lower amount than in the commercial fish sauce (p < 0.05). Thus, H. salinarum accelerated protein hydrolysis and produced desirable volatile compounds during fish sauce fermentation in a strain-specific manner.