Screening and identification of acetoin-producing Bacillus and effects of different inoculation time on solid-state fermentation of fermented grains

Acetoin-producing Bacillus were screened from the fermented grains of sauce-flavor (Jiangxiangxing) Baijiu. The strains were identified through morphological observation and molecular biology techniques. Using uninoculated fermented grains as a control, the selected strains were inoculated into a solid-state fermentation system of fermented grains at different fermentation time (12 h, 24 h, 48 h), to investigate the effects of different inoculation time on the physicochemical indexes, organic acid content, and volatile flavor compounds during fermentation. The results showed that an acetoin-producing strain YH403 was isolated and identified as Bacillus amyloliquefaciens. The fermentation performance of fermented grains of strain YH403 inoculated at 24 h was significantly improved. Compared with the blank group without inoculation, the pH value, water content and reducing sugar content of fermented grains of strain YH403 inoculated at 24 h were improved, which promoted the synthesis of L-lactic acid, acetic acid, succinic acid, citric acid and L-malic acid in fermented grains. The contents of total volatile flavor substances in fermented grains of strain YH403 inoculated at 24 h were significantly increased, especially the contents of esters, pyrazines, alcohols and acetoin were significantly increased, and the contents of acetoin in fermented grains of strain YH403 inoculated at 24 h were twice that of the blank group. Moreover, the synthesis stability of volatile flavor substances was also enhanced.