Abstract: High-salt-tolerant ethanol-producing mutant L6-1 was obtained by ultraviolet mutagenesis of Zygosaccharomyces rouxii L6, isolated from soy sauce mash in our previous work, followed by screening using 2,3,5-triphenyltetrazolium chloride (TTC) plates. it could accumulate 2.71% (V/V) ethanol in bean sprout juice medium with 10% (m/m) NaCl, which increased by 54.86% as compared with that of the original strain L6. On day 45 of the 90-day fermentation period, L6-1 accumulated the highest amount of ethanol (up to 1.00%) in high-salt fermented mash, which increased by 78.57% as compared with that of the control group. A total of 47 volatile flavor compounds (VFCs) were detected in the mash fermented by L6-1 using solid-phase microextraction followed by gas chromatography-mass spectrometry (SPME-GC-MS) method, as opposed to 27 VFCs in that fermented by L6. The L6-1 fermented mash contained two more esters, ten more alcohols (excluding ethanol), four more aldehydes, one more phenol, and three ketones compared with the L6 fermented mash. The total ethyl ester content of the L6-1 fermented mash was 605.64 ng/g, which increased by 6.79% and 20.61%, respectively compared with the L6 fermented mash and the control not inoculated with yeast. Furthermore, principal component analysis (PCA) showed that the L6-1 fermented mash scored the highest. In addition to increasing the types and contents of alcohols (mainly ethanol), L6-1 could promote the formation of esters as the major aroma components of soy sauce especially ethyl esters, indicating that L6-1 could improve the alcoholic aroma and effectively enhance the richness of soy sauce flavor.

Key words: soy sauce brewing; salt-tolerant ethanol-producing yeast; breeding; volatile flavor materials; high-salt liquid-state fermentation