Determination of High-risk Stages of Moldy during the Curing Process of Yunnan Cigar Leaves and the Identification of Major Molds

To clarify the high-risk mold growth stages and mold types during the curing process of cigar leaves, and to provide guidance for the prevention and control of mold growth, this study investigated the cigar leaves at different curing stages in Yuxi, Yunnan. The mold quantity at different curing stages LZ0d (fresh tobacco leaves), LZ8d (curing 8 d, yellowing stage), LZ19d (curing 19 d, browning stage), LZ26d (curing 26 d, dry-tending stage) was preliminarily determined to be high-risk mold growth stages through the 3M Petrifilm^TM count plate. The main types and proportions of molds at different curing stages were obtained through plate dilution culture, and the main mold types were identified through morphological and molecular biology methods. Key findings are as follows: (1) The counting plates showed that the high mold counts were observed at LZ8d, LZ19d and LZ26d stages, indicating these are the high-risk mold growth stages during curing; (2) The main mold species during the curing stage of cigar tobacco leaves in Yuxi, Yunnan were Cladosporium tenuissimum, Letendraea cordylinicola, Penicillium rubens, Stagonosporopsis crystalliniformis, Aspergillus ochraceus, and Aspergillus flavus. The mold species varied across curing stages. Among them, C. tenuissimum strain was present in LZ0d, LZ8d, and LZ19d samples, with proportions of 70%, 50%, and 30% respectively, showing a gradual decrease trend; Penicillium rubens was present in LZ8d, LZ19d, and LZ26d samples, with proportions of 15%, 40%, and 45% respectively, showing an increasing trend; (3) The dominant molds were sensitive to high temperatures, particularly L. cordylinicola, S. crystalliniformis, and C. tenuissimum, as mold growth could be inhibited by raising the temperature to 34~37 ℃. The six mold strains showed minor differences in growth under different pH conditions. In summary, the yellowing (LZ8d), browning (LZ19d) and drying-tending (LZ26d) stages of curing cigar leaves in Yuxi, Yunnan are particularly susceptible to mold growth due to high mold counts. Different curing stages have a succession of main mold species. Raising the temperature appropriately during tobacco leaf curing is expected to inhibit mold growth and reduce the risk of mold growth.