Screening of Functional Strains in Traditional Brewed Soy Sauce and Their Fermentation Characteristics

In order to investigate the influence of enzyme high-yielding strains on the brewing efficacy during soy sauce fermentation, a total of 213 strains were isolated and screened from high salt liquid sauce, and the strains with high productions of protease, amylase, cellulase, and lipase were further screened and identified. Subsequently, an 8 day rapid fermentation experiment was conducted to investigate the fermentation characteristics of these strains. The headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was employed to determine the content of volatile flavor compounds in the fermentation. The results showed that 6 strains of high-yield of enzymes were obtained through initial screening, re-screening and identification, including 5 strains of Bacillus and 1 strain of Enterobacterium. After rapid fermentation, it was found that the content of reducing sugar was highest (0.49 mg/mL) in the fermentation broth of Bacillus T4 strain with high yield of protease. The content of phenolic volatile substances was highest in the fermentation broth of Bacillus T13 strain with high amylase content. The content of amino acid nitrogen reached 0.428 mg/mL in the fermentation broth of Enterobacter T11 strain with high cellulase production, and the contents of pyrazine and alkene flavor compounds were the highest. As for Bacillus T15 strain with high lipase production, there were high levels of esters and ketones in the broth. The volatile flavor compounds generated by single strain fermentation exhibited certain preferences in specific categories, while mixed strain fermentation was generally superior to single strain fermentation. This study not only provides reference for improving soy sauce quality and enabling targeted flavor modulation, but also augments soy sauce strain resources, which is beneficial for the research and development of high-quality soy sauce.