Isolation, Identification, Optimization of Fermentation Conditions and Application of β-Phenylethanol-producing Yeast from Natural Soy Sauce Mash

To improve the quality of soy sauce, this paper presented a study on the production of β-phenylethanol by Zygosaccharomyces rouxii and its application in the brewing of high-salt liquid-state fermented soy sauce. The β-phenylethanol-producing yeast strain J13, screened from natural sauce mash, was identified by morphological observation, physiological and biochemical results and molecular biological methods. The biological characteristics of Z. rouxii 13 through salt tolerance, pH tolerance and temperature tolerance analysis were studied. A series of single-factor and orthogonal tests were conducted to get the optimized medium composition and fermentation conditions for this strain. Z. rouxii 13 was then cultured under the optimal fermentation conditions to obtained flavor liquid and applied to the brewing process of high-salt liquid-state fermented soy sauce. The results showed that J13 was identified as Zygosaccharomyces rouxii, named Z. rouxii 13 accordingly. Z. rouxii 13 could successfully grow under high salinity (18% NaCl) conditions. The optimum pH was 4~8 and the optimum temperature was 25~35 ℃. Under the optimal fermentation conditions: L-phenylalanine concentration of 4 g/L, glucose concentration of 30 g/L, peptone concentration of 10 g/L, magnesium sulfate concentration of 0.5 g/L, dipotassium hydrogen phosphate concentration of 5 g/L, NaCl concentration of 50 g/L, pH6.0, and temperature of 28 ℃, the highest content with β-phenylethanol of 1.40 g/L was obtained. The flavor liquid was applied to soy sauce brewing and the finished products were obtained. The sensory evaluation showed that the flavor liquid group had more prominent soy sauce flavor and fullness, and better umami and overall evaluation compared with the control group that without flavor liquid.