Effects of 60Co-γ ray irradiation on microorganisms,metabolites and quality of cigar tobacco during the fermentation
[Purpose]We used 60Co-γ rays to sterilize bacteria,clarifying the significant role of microorganisms in cigar tobacco leaf fermentation process.[Method]Cigar tobacco leaves of the Dexue No.1 variety were fermented following 10k Gy of 60Co-γ ray irradiation.Microbial diversity,metabolomics,neutral aroma components,alkaloids,and other indices of cigar leaves were measured and analyzed during fermentation.[Results]1)No bacterial community was detected in irradiated cigar leaves fermented for 28 days,as determined by traditional isolation culture and Illumina MiSeq high-throughput sequencing.2)Non-targeted metabonomics showed higher levels of polyphenols,such as rutin,astragaloside,phloridzin,kaempferol,kaempferol-3-O-rutinoside,and dipeptides in irradiated tobacco leaves after 28 days of fermentation compared to non-irradiated leaves..Meanwhile,levels of amino acids like leucine,L-serine,and proline were lower..Metabolic pathways showing significant differences in KEGG enrichment included flavonoid and flavonol biosynthesis,and arachidonic acid metabolism.3)After 28 days of fermentation,significant reductions were observed in total alkaloids,reducing sugars,total sugars,starch,and protein content in both groups of tobacco leaves.The decrease in these indicators was less pronounced in irradiated leaves compared to non-irradiated leaves.After 28 days of fermentation,irradiated leaves had significantly lower neutral aroma components but higher browning reaction products,resulting in greater vitality,impurities,and irritability in cigar leaves.[Conclusion]A 10kGy dose of60Co-γ ray irradiation effectively sterilized the cigar leaves before fermentation.After 28 days of fermentation and transformation of macromolecules in irradiated leaves were lower than in non-irradiated leaves,leading to a reduced increase in sensory quality..Despite this,the quality of irradiated leaves still showed some improvement compared to non-fermented tobacco.
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