Optimization of solid-state fermentation process for low-grade tobacco leaves by mixed strains of Bacillus amyloliquefaciens and Saccharomyces cerevisiae

Using volatile aromatic components content as evaluation index, the fermentation process conditions of low-grade tobacco leaves by mixed strains of Bacillus amyloliquefaciens JL-4 and Saccharomyces cerevisiae PY-1 were optimized through single-factor experiments and orthogonal experiments. The volatile aromatic components in the fermented tobacco leaves were detected by simultaneous distillation and extraction combined with GC-MS, the physicochemical indicators were measured, and the sensory evaluation was conducted. The results showed that the optimal mixed solid-state fermentation conditions for low-grade tobacco leaves were mixed strains ratio (strain JL-4∶strain PY-1) 2∶1, fermentation temperature 33 ℃, and inoculum 24%. Under these conditions, the content of volatile aromatic components in low-grade tobacco leaves reached the highest (565.47 μg/g). Compared with low-grade tobacco leaves solid-state fermented with sterile water, strain JL-4 and strain PY-1, the contents of volatile aromatic components in low-grade tobacco leaves through mixed solid-state fermentation increased by 30.44%, 9.94% and 12.42%, respectively, the starch contents decreased by 31.04%, 5.27% and 30.71%, respectively, the total content of water-soluble sugar increased by 14.85%, 6.55% and 9.07%, respectively, and the sensory evaluation score increased by 51.35%, 12.00% and 16.67% respectively, the smoking quality was significantly enhanced, with the aroma temperament and aroma quantity being significantly improved, the aftertaste was better, and the irritation and impurity being reduced. In conclusion, the low-grade tobacco leaves were fermented with mixed strains of B. amylolyticus and S. cerevisiae (2∶1), which could endow tobacco leaves with unique aroma components, significantly reduce the starch content and improve the smoking quality of tobacco leaves.