Improvement of tobacco upper leaf quality after fermentation by Saccharomyces cerevisiae and its association with microbial community

Tobacco (Nicotiana tabacum. L) is an important cash crop in China, but there are some problems such as lack of aroma and uncoordinated chemical composition in the upper tobacco leaves. In order to ensure the demand of the tobacco industry for high-quality upper tobacco raw materials, a previously screened strain of Saccharomyces cerevisiae Z2 was selected as the fermentation strain for improving upper tobacco leaves. The upper tobacco leaves of GZ36, K326, and Yunyan 87 (Y87) were used as research materials, the best inoculation conditions were selected by orthogonal test. We inoculated the tobacco leaves with S. cerevisiae before curing, the quality of tobacco leaves were measured after curing, and the changes of microbial community in tobacco leaves were studied by high throughput technology. Lastly, the correlation between the microbial communities and the quality of tobacco leaves were been clarified. The results showed that the optimal inoculation conditions for S. cerevisiae to inoculate tobacco leaves were: inoculation concentration 106 CFU/mL, inoculation volume 10 mL, and processing time 2 h. After being treated with S. cerevisiae Z2, the aroma quality of tobacco leaves was improved and the impurity was reduced. The content of total sugars, reducing sugars, total nitrogen, starch, and total alkaloids decreased significantly, and the chlorine and potassium content increased in flue-cured tobacco. The internal chemical coordination of GZ36 and Yunyan 87 tobacco significantly improved. The richness and diversity of tobacco bacterial community increased, while the diversity of fungi increased and richness decreased. Redundancy analysis and molecular ecological networks showed that the sensory quality and chemical composition were correlated with dominant species, the aroma quantity, aftertaste, nicotine, and reducing sugars were the most significant factors correlated with microbial communities. This study showed that S. cerevisiae could significantly improve the quality of tobacco leaves, change the microbial community, and occupy a dominant position. The results provided a scientific reference for improving the overall quality and economic benefit of tobacco leaves.