Effects of Different Fermentation Methods on the Quality and Flavor Metabolic Characteristics of Cigar Filler Leaves

To investigate the effects of different fermentation methods on the quality formation of cigar filler leaves and their underlying mechanisms, this study systematically analyzed the differences in temperature and humidity dynamics, chemical composition, appearance, and sensory quality of tobacco leaves among natural fermentation (NF), stacking fermentation (DJF), medium fermentation (JZF), and oak barrel fermentation (XMF), and analyzed their metabolic profiles and flavor characteristics using untargeted metabolomics and gas chromatography- ion mobility spectrometry (GC-IMS). The results showed that in the microenvironments of the four fermentation methods differed significantly: NF exhibited low and stable temperature and humidity; DJF showed large temperature fluctuations and relatively low humidity; JZF experienced rapid temperature rise and high humidity, indicating vigorous fermentation; and XMF maintained moderate and stable temperature and humidity. Artificial fermentation significantly promoted the transformation of chemical components in tobacco leaves, with XMF showing the most complete degradation of total sugars, reducing sugars, nicotine, and polyphenols. The appearance quality score ranked as JZF > DJF > XMF > NF. XMF demonstrated the best performance in aroma and aftertaste characteristics, achieving the highest overall sensory score. XMF produced more differential metabolites (391 non-volatile and 161 volatile) than DJF (213, 173) and JZF (173, 127), and these were mainly enriched in key flavor-forming pathways such as diterpenoid biosynthesis and nucleotide metabolism. GC-IMS analysis showed that DJF had higher levels of substances such as (Z)-2-pentenal, which imparted green and pungent notes to the tobacco leaves; JZF had a relatively higher content of (E)-2-butenal, associated with scorch; while XMF produced a richer and more harmonious fruity, grassy, and honey-sweet flavor profile. In summary, different fermentation methods, by creating distinct fermentation micro environments, mediate differential metabolic pathways of tobacco chemical components, thereby determining the final quality and flavor characteristics.