Effects of Microbes and Metabolites on Tobacco Quality in “Humi” Characteristic Fermentation of Cigar Tobacco Leaf

Fermentation is an important link in the process of cigar production, which directly determines the quality of tobacco leaves. “Humi” fermentation is a traditional method of manually adding materials, which can highlight the aroma characteristics and improve industrial availability of tobacco leaves. However, the mechanism of “Humi” fermentation is still unclear. This study was aimed to explore the effect of the “Humi” characteristic fermentation on the quality of cigar leaves, and the potential mechanisms. Cigar variety Dexue 1 was used. Three degrees of “Humi” water were prepared and water was used as control. 16S rDNA sequencing and metabolomics analyses were carried out to determine the changes in microbes and metabolites during fermentation. “Humi” fermentation significantly improved the evaluation quality of cigar tobacco. The microbial richness and community diversity in “Humi” fermentation group were higher than that in natural fermentation group. Total 214 genera were detected, with Staphylococcus, Corynebacterium_1, and Oceanobacillus as the dominant genera in the “Humi” fermentation group. With the extension of fermentation time, the relative abundance of Corynebacterium_1 increased, and of Oceanobacillus and Staphylococcus first increased and then decreased. Moreover, Corynebacterium_1 were significantly negatively correlated with total nitrogen, protein and alkaloid content, and significantly positively correlated with amino acids, starch, reducing sugars and total sugars. Metabolome analysis revealed 2,759 known metabolites in 36 samples and “Humi” fermentation increased the nitrogenous heterocyclic compounds, sugars, alkaloids and organic acids in tobacco leaves. These metabolites were closely related to the bacterial community. Our study provides a theoretical basis for inheriting and optimizing the “Humi” characteristic fermentation technology.