The influence of fermentation process optimization of Bacillus subtilis 1-F-2 on the quality, flavor, and sensory properties of cigar tobacco leaves based on response surface methodology

Fermentation was a crucial process determining the final quality of cigar tobacco leaves (CTLs). In this study, an aroma-producing strain was identified as Bacillus subtilis and designated 1-F-2. To investigate the influence of inoculated fermentation on the quality of CTLs, the optimal fermentation conditions were determined by integrating single factor experiment with response surface methodology (RSM). The physicochemical properties, volatile flavor compounds (VFCs), and sensory properties of the fermented CTLs were systematically characterized. RSM revealed that the optimal parameters were 36 °C, 2 × 10⁷ CFU/g, 22 days. Compared with the non-inoculated fermentation group (CK), the nitrogen, nicotine, reducing sugar, and total sugar contents of the CTLs fermented with B. subtilis 1-F-2 decreased. The diversity and concentration of VFCs increased significantly, with the total content rising by 74.51% compared to the CK ( P < 0.05). Relative odor activity value (ROAV) analysis had confirmed the marked enhancement of key VFCs. Notably, acetophenone emerged as a new contributor, while the ROAV of ( E )-6,10-dimethyl-5,9-undecadien-2-one rose from 0.54 to 1.26, and β-damascenone (ROAV = 100) remained the predominant contributor, imparting intense fruity and floral notes. The sensory evaluations showed significant improvements in aroma complexity, smoke smoothness, and aftertaste, which were characterized by enhanced nutty and honey-sweet notes alongside emerging coffee, cocoa, and dry hay nuances. These enhancements were attributed to the elevated levels and rebalanced proportions of key VFCs, in which the increased contributions of acetophenone and the undecadienone derivative effectively complemented the dominant β-damascenone. This work provided a valuable framework for improving the quality of CTLs via targeted microbial fermentation.