Correlation between Microbial Diversity and Flavor Substances on the Surface of Flue-Cured Tobacco

Tobacco leaves need to aged under certain temperatures and humidity for 1 to 3 years. Natural aging, also called fermentation, is a slow process. This article explores the correlation between microorganisms on the surface of flue-cured tobacco and key flavor substances during this process. High-throughput sequencing was used to characterize the composition of bacterial and fungal communities on the surface of flue-cured tobacco from Hunan, Liaoning, Guizhou, Shandong, Yunnan, Fujian, Brazil, and Zimbabwe. Gas chromatography-mass spectrometry (GC-MS) was employed to determine the flavor substances in flue-cured tobacco and correlation analysis between microbial diversity and flavor substances was performed. The function and abundance of key enzymes involved in the degradation of macromolecules on the surface of flue-cured tobacco were predicted using PICRUSt and FUNGuild. Different flavor styles of flue-cured tobacco possessed different flora structures, and the abundance of the genus Bacillus was high and significantly positively correlated with the content of the main flavor substances-carotenoid and cembranoid degradation products (p < 0.05). The content of the Enterobacter genus was higher in light-flavor style flue-cured tobacco and significantly negatively correlated with the above substances (p < 0.05). Among the fungal genera, Wallemia exhibited a significantly positive correlation with phenylacetic acid, palmitic acid, and & alpha;-ionol (p < 0.05). The abundance of the macromolecule-degrading enzymes in the bacterial community was generally higher than in the fungal community, especially the enzymes that hydrolyzed, transferred, and isomerized starch, protein, and cellulose. Classifying the tobacco leaves according to the flavor style revealed that the expression levels of a series of enzymes acting on pectin hydrolysis and cleavage and laccase were higher in strong-flavor flue-cured tobacco. This study explored the microorganisms related to the key substances of flue-cured tobacco and provided a theoretical basis for using microorganisms to improve the flavor.