Pigment Changes And Their Mechanisms Of Flue-Cured Tobacco Leaf During Maturing And Curing Phases

The conditions during the maturing and curing stages had great effects on the degradation and transformation of the pigments of the flue-cured tobacco leaf. Different harvesting time and curing measures would impact on the degradation of pigments, and then affected the transformation of precursor and the final aroma quality of flue-cured tobacco. Based on research on the characteristics of pigment changes and their mechanisms during maturing and curing stage, this paper mainly focused on the characteristics of color change with different maturity degree, the pigment changes and their mechanisms, the relationship between color, physiology and texture during curing. The principal conclusions are as follows:1. The contents of pigments in flue-cured tobacco gradually decreased during the growing and maturing stage, and the ratio of fertilizer had some impacts on its degradation. The chlorophyll and carotinoid content of treatment B (30%:70% ratio of inorganic fertilizer to organic fertilizer) were significantly higher than the other two treatments during the early growth stage, while its contents were lower during the late growth stage, and the abundant degradation of pigments during maturing stage was good to the quality of tobacco. Chlorophyllase and LOX activity of treatment B were lower at the early maturing stage, and rose obviously at the later maturing stage, while the activity of POD was to the contrary. Higher activity of POD and lower activity of LOX during the early stage were helpful to improve resistant ability and decrease membrane lipid peroxidation, and the higher activity of Chlorophyllase and LOX were favorable to the degradation of pigments.2. The value of L* with different maturity degree during curing were overripe> ripe> unripe> immature. The value of a* had no evident difference compared with different maturity, while the value increased rapidly before the mid-term of yellowing for those had high level of maturity. The overriped tobacco had higest value of b*, then followed the ripe, unripe, and immature. The b* increased before the mid-term of color-fixing in all treatments, and then decreased at the later stage of color-fixing. The correlation analysis showed that the content of carotenoid and L* of leaf blade had significant negative correlation between the tobacco of unriped and riped, and the content of carotenoid and a* of leaf blade had significant negative correlation. Taking the riped tobacco for example, the regression equation between carotenoid and the parameter of leaf color was y=-0.017 L*+0.016 a*+0.003b*4+1.203, R2=0.993. The parameters of leaf color and pigment contets had evident correlation for overriped tobacco. It was feasible to use the colorimetric values as an auxiliary pointer to determine the tobacco maturity.3. The contents of carotenoids degraded gradually accompanying with curing process in the yellowing stage. The contents of the lutein, neoxanthin, violaxthin decreased gradually in the yellowing stage following the decrease of temperature and humidity. The treatment of low temperature and medium humidity condition is conducive to the degradation of carotenoids. Carotenoids degradation is not a single enzyme resulted, Lipoxygenase (LOX), Phenylalanine ammonialyase (PAL), Peroxidase (POD), Polyphenol oxidase (PPO) are common results to the degradation of carotenoids. Great differences existed in the enzyme activities between different treatments, the treatment of low temperature and medium humidity condition can properly coordinate the enzyme activities. The activities of LOX and POD could express fully, meanwhile the carotenoids degraded fully. Correlation analysis showed that there were highly significant relationship between the activities of POD and the carotenoids components in the yellowing stage during the curing process. If the high activities of lipoxygenase and peroxidase are prolonged longer appropriately at 36-48 h under low temperature and relatively low humidity in the yellowing stage and the effect between the cooperative and antagonism reaches to dynamic balance, it would be benefit to degrade carotenoids sufficiently and improve the aroma quality of tobacco leaves.4. The contents of carotenoids decreased gradually at color-fixing stage during curing process; the decrements of carotenoids components of the slow heating treatment were relatively large, though there were no differences among treatments. Effects of different conditions of curing on the activities of enzymes were significant and lipoxygenase, phenylalanine ammonialyase, peroxidase and polyphenol oxidase had a bidirectional effect on the quality of tobacco leaves. It was beneficial to form more premise matter of aroma based on the higher enzymes activities at early leaf-drying stage. The slow heating could regulate the changes of various enzymes activities reasonably, make cell redox reaction reach to dynamic balance and make the degradation of carotenoids adequately. Meanwhile it could avoid the occurrence of browning reaction and provide a reference to improving the quality of tobacco.5. The carotenoids contents were very significantly correlated withβ-carotene content in flue-cured tobacco, and these two pigments contents had significant negative correlation with carotenoids degradation products. Theβ-carotene content ratio was lowest, but lutein neoxanthin and violaxanthin content ratios were higher in flue-cured tobacco leaves with the treatment of low temperature with middle humidity. The treatment of low temperature with middle humidity had the highest aroma components contents. At the same time, the contents of 6-methyl-5-hepten-2-ketone, P-damascenone, dihydroactinolide etc., were also highest between the six curing teratments.6. Using principal component subset selection method, five kinds of aroma components were selected out from the 26 kinds of aroma components detected in tobacco leaves. These components were Benzaldehyde,5-methyl fufura,3,4-dimethyl-2,5-dione furan, Geranyl acetone, and Solavetivon. Because these five kinds of aroma components covered 83.4% information of the total 26, so we used them to establish a model for assessing and ranking the aroma quality of tobacco leaves. The aroma quality assessment result was ranked as low temperature with medium humidity> low temperature with low humidity> high temperature with high humidity> low temperature with high humidity> high temperature with medium humidity> high temperature with low humidity. The best curing method to improve the aroma quality of flue-cured tobacco has been determined.7. The correlation between pigments and colorimetric values during curing were better, and the pigments had positive correlation with h, one of the colorimetric parameter, and negative correlation with the other colorimetric parameters. The correlationships between texture and colorimetric parameters were feeblish. Differences in the changes of colorimetric and texture between varieties, the values of L*, b* of Qinyan 96 were always higher than those of Zhongyan 100 during curing. Meanwhile, the values of a* and C* of Qinyan 96 were also higher than those of Zhongyan 100 in cured tobacco. The hue angle of Qinyan 96 vary considerably, but its tonal value had no evident difference in cured tobacco. The texture of Qinyan 96’s cured tobacco was loosen, and the value of hardness, chewiness and resilience were relatively low.8. Texture parameters of tobacco leaves during curing stage changed greatly from the mid-term of yellowing to the mid-term of color-fixing, of which cell wall bound enzymes were higher. The changes of cell wall matter and water content were obvious too. The dynamic variations of cutting force during curing were intuitively, and the resilience and pull were better textural parameters to researching the change of tobacco cell physiology. The changes of cell physiology (water, respiratory rate, enzymatic activities and their component) were the major factors which caused the differences in tobacco texture during curing.