Effects of adding fermented grains and summer-autumn tea on the quality of agricultural fermentation of filler tobacco leaves

In response to the issue of weak style characteristics of raw materials of domestic cigar, using the addition of ultrapure water as a control, the effects of exogenous additives in fermented grains and summer and autumn tea on the basic physicochemical indicators and flavor during the agricultural fermentation process of filler tobacco leaves were investigated by conventional detection methods, amino acid automatic analyzers, electronic nose and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The effect of physicochemical indicators on key differential flavor metabolites was clarified through correlation analysis. The results demonstrated that exogenous additives facilitated the degradation of reducing sugars, delayed total sugar consumption, reduced pH, starch, and protein content during the mid-fermentation stage, and increased total acid content. Based on the taste activity value (TAV) ≥1, the variable importance in projection (VIP) value≥1, and P＜0.05, it was screened that glutamic acid, proline, and threonine were the key flavor amino acids that caused the taste differences of different treated tobacco leaves, jointly endowing the umami, sweet, and bitter characteristics of the filler tobacco leaves. The exogenous additives also promoted the degradation of nitrogen oxides, balanced the aroma composition, and enhanced the floral, fruity, sweet, waxy, and musky flavors of tobacco leaves. Based on the odor activity value (OAV)≥1, VIP≥1 and P＜0.05, 8 substances such as 4,7,9-megastigmatrien-3-one and 4-oxoisophorone were screened out as the key volatile flavor substances causing the odor differences of tobacco leaves treated with different methods. The results of the correlation analysis indicated that exogenous additives affected the generation of key differential flavor metabolites by reducing the pH and increasing the total acid content of tobacco leaves.