| The effect and mechanisms on improvement of sweet-smelling quality of Virginia-type cigarette induced by the two fungal strains, BF06 and BF07, were studied. BF06 and BF07 were identified as members of Hyphomycetes and Zygomycetes, respectively.The biological characteristics of BF06 and BF07 had been clear. To the strain BF06, the better conditions, which can induce the sweet-smelling, are in the carbon resource from fructose, in the nitrogen from potassium nitrate, at pH=8.0, in PDA 8-10 days cultivate at 27.5 ℃. While to the strain BF07, the better conditions are in the carbon resource from fructose, in the nitrogen from ammonium sulphate, at pH=6.0, in the LB 8-10 days cultivate at 35.0°C.To test and verify the true effect of the two fungal strains on improvement of sweet-smelling quality of the cigarette the sprying of the cultivating metabolites produced by BF06 and BF07 on leaves at upper and middle plant parts of the tobacco tested in different growing stage were caried out, respectively. The total volume of the sugar, the reductive sugar, the nitrogen, the protein and the nicotinamide etc.were determined by using auto-near-infrared auto-instrument. The results indicated that the ratios of the sugar/ nitrogen, the sugar/ nicotinamide and the nitrogen/ nicotinamide are all being more close to the standard of high quality tobacco than that occurred in CK.Based on the assessment of the authoritative savour experts, the cigarettes made of tobacco treated with BF06 and BF07 are all better than that made of CK leaves in their fragrance.According to the determinations before curing, the kinds and content of the volatile materials in the middle leaves of the two tobacco cultivars, K236 and Yunyan 85, treated with metabolites of BF06 and BF07, were obviously increased and the new ones, which hold 29.01% in the total volatile materials, occurred compared with the untreated leaves (CK). The quantities of the natural substances such as alcohols, ketones, aldehyde and the ester precursors etc. which are essential for the synthetizing of sweet-smelling matters in the leaves were increased in the treated leaves. In some treatments the content of nicotinamide was decreased in some degree.The determinations showed that the activities of proteases, α -amylases, cellulases and peroxidases in the leaves treated in the early and middle growing stage were obviously increased in certain periods. This indirectly indicated that there were some interrelationships between the accumulation of the kinds and content of the volatile materials and the increase of the enzyme activities in the leaves treated with BF06 and BF07. The test also revealed that the activity of polyphenol oxydase was not increased or even lower than that in the untreated leaves (CK). This might be advantageous to reduce the over oxidizing of the phenolic matters during the stages of curing and fermenting of tobacco leaves. Therefore, the tobacco leave browning due to the over accumulation of the quinones might be avoided.The TEM observation showed that the amylogranules in the leave cells treated with BF06 and BF07 had been notably reduced as compared with the untreated samples (CK). It is consistent with the results of amylase testing.The security of two fungal strains had been assessed. They had never caused any tobacco diseases and being moldy in growing season and during the periods of curing and manned- zymolysis. After curing the fungi used for treatment were all deactivated, and no any...
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