Screening for Thermoactinomyces vulgaris in Fermented Grains of Sauce-Flavor Baijiu and Metabolic Analysis of Volatile Compounds

In order to screen for potential Thermoactinomyces from stacked fermented grains of sauce-flavor Baijiu, three strains of Thermoactinomyces valgaris were obtained by enrichment and isolation and identified by morphology and molecular biology. The metabolic characteristics of volatile compounds produced in liquid-state fermentation by each strain were investigated. Additionally, solid-state fermentation experiments were performed at 45 or 50 ℃. The flavor metabolism profiles of each strain at different fermentation stages were analyzed and summarized under liquid-state and solid-state fermentation conditions. The results showed that all three T. vulgaris strains grew rapidly in the liquid medium. They entered the logarithmic growth phase between 10 and 16 h and attained the stationary phase at 34 h, and the accumulation of acidic substances and pyrazines was enhanced. Specifically, strain ts5 displayed the highest concentrations of 2-methyl butyric acid and 2,3,5-trimethylpyrazine, amounting to 4.14 and 0.72 mg/L, respectively. The total quantity of volatile compounds produced in solid-state fermentation gradually ascended over the fermentation period. Notably, solid-state fermentation at 50 ℃ enabled a more substantial accumulation of flavor compounds such as esters, phenols, and pyrazines in comparison with that at 45 ℃. Collectively, the aroma production of T. vulgaris in solid-state fermentation on Hongyingzi sorghum was superior to that in liquid-state fermentation. Moreover, fermentation at 50 ℃ was more conducive to the accumulation of flavor compounds when compared with 45 ℃. The results of this study provide a theoretical basis for understanding the aroma-producing performance of T. vulgaris during high-temperature stacking fermentation.