Improved accumulation of organic acids and amino acids in Saccharomyces cerevisiae by GREACE and its application in enhancement of kokumi and umami in soy sauce

This study aimed to improve the concentrations of organic acids and amino acids in Saccharomyces cerevisiae for application in enhancement of kokumi and umami in soy sauce by Genome Replication Engineering Assisted Continuous Evolution combined with high-salinity screening. The concentrations of succinic acid, amino acid nitrogen and total acidity in evolved strain G1.6-15 reached 620.1 mg/L, 13.56 mg/g and 281.3 mg/g, which were 146.1%, 47.2% and 57.4% higher than parental G100. Its biomass and succinic acid titer reached 57.8 g/L and 9.6 g/L after fed-batch fermentation in 5 L fermenter for 60 h. After preparation into compound fermentation-derived flavor enhancer (CFE), the concentrations of total free amino acids and succinic acid in CFE-G1.6-15 were 85.35 mg/g and 145 mg/g, which were 36.4% and 520% higher than CFE-G100. When applied in soy sauce, CFE-G1.6-15 exhibited superior taste enhancement than pure succinic acid at the same addition levels while synergistic effect was observed between organic acids and amino acids. CFE-G1.6-15 significantly improved the umami , kokumi and sweetness of soy sauce, reduced saltiness perception and increased the quantities and concentrations of volatile flavor compounds. Fractionation experiments further revealed that extracellular organic acids, especially succinic acid, in CFE dominated the kokumi enhancement while amino acids mainly contributed to umami and sweetness improvement. This study provided a non-GMO, efficient and industrial feasible technical approach for preparing high-flavor CFE and improving the flavor profile of soy sauce.