| To investigate the main curing characteristics and correlation of the upper leaves of flue-cured tobacco Yunyan 87.The laws of the upper leaves of Yunyan 87 darkened and browned,the change of water content,the change of color,and the main physiological and biochemical changes from the beginning of curing to the end of fixing color were studied by using the darkened box and intensive curing methods,and the correlation was analyzed.The main research results are as follows:（1）The upper leaves of Yunyan 87 have good easy curing potential and medium curing potential and medium curing characteristics.（2）During the curing process of the upper leaves of Yunyan 87,the water loss rate showed a"slow-fast-slow"trend.The water loss rates were 0.38%/h,0.55%/h and 0.16%/h,respectively,from the early yellowing stage to the middle yellowing stage,from the late yellowing stage to the middle fixed color stage,and from the late fixed color stage.The total water loss was 77.2%at the end of the fixed color stage;PPO activity showed a trend of"downward-upward-down",that is,it slowly decreased before the middle stage of yellowing,then increased rapidly,then decreased sharply after reaching the peak at the end of yellowing,and gradually stabilized at the late stage of fixing color;The change trend of POD and SOD activities was similar to that of PPO,but the peak value was earlier than that of PPO.The activity of amylase showed a double peak curve of"ascending-descending-ascending-descending",and reached the peak value at 36h and 84h,respectively.The content of MDA showed a"slow-fast-slow"increasing trend,that is,it increased slowly before the middle yellowing stage,rapidly increased during the early yellowing stage and gradually stabilized in the late yellowing stage;The contents of total nitrogen,potassium,nicotine and petroleum ether extracts were increased by 11.92%,17.36%,17.54%and 30.95%,respectively,compared with fresh tobacco leaves at the end of fixing;Starch content showed a"fast-slow"decreasing trend,which was mainly degraded in the early yellowing stage,and the total degradation was80.13%at the end of color fixing;The content of total sugar and reducing sugar showed a"quick-slow"increasing trend,and the increasing rate was faster in the middle stage before turning yellow,and increased by 83.42%and 77.97%respectively at the end of fixing color compared with fresh tobacco leaves;The degradation of protein was fast in the middle stage of yellowing,and gradually slowed down after the late stage of yellowing.The total degradation amount was 36.37%at the end of color fixing;The content of total phenol showed a trend of"rising,falling and rising",which increased slowly before and during the middle stage of yellowing,then decreased slowly,reached the lowest value in the early stage of fixing color,then increased rapidly,and increased by 54%compared with that of fresh tobacco at the end of fixing color;The total chlorophyll,chlorophyll a,chlorophyll b and SPAD showed a"fast-slow"decreasing trend,and the degradation rate was fast in the early yellowing stage,and then tended to be stable after the fixed color stage;The total degradation amount was 90.5%,85.53%,93%and 84.7%,respectively,at the end of fixed color stage;Carotenoids showed a slow downward trend,but the degradation was mainly concentrated before the middle yellowing stage,and then tended to be stable at the end of the fixed color stage,with the total degradation of 43.9%.（3）Simple correlation analysis showed that water content was significantly correlated with PPO and MDA content in each stage of curing process;And SOD activity were significantly negatively correlated and extremely significantly positively correlated(r=-0.794*,0.938**)from late yellowing stage to early coloration stage,respectively.And POD activity was significantly positively correlated at the later stage(r=0.907**).And amylase in the early stage,color yellow,late before respectively,has negative correlation significantly positive correlation(r=0.784*,0.938**,0.911**),therefore,upper leaves in the curing process for tobacco leaf oxidative aging,in particular,should pay attention to the yellow late-set the color of water regulation,especially for large molecules decomposition should pay attention to the early stage of the yellow and the color of water regulation.（4）Principal component analysis showed that 3 factors were extracted from 14 chemical components in the curing process,with a contribution rate of 88.06%,of which factor 1 mainly represented plastid pigment and carbohydrate,factor 2 mainly represented petroleum ether extract,and factor 3 mainly represented total nitrogen.（5）Grey correlation analysis showed that the main chemical components in the curing process were carotenoids which had a close relationship with the activities of PPO,SOD and POD,and total nitrogen which had a close relationship with amylase.The grey correlation degree of POD,SOD activity,PPO activity and MDA content all showed that SOD>POD,and POD mainly played a defensive role in the early yellowing stage,SOD mainly played a defensive role in the late yellowing stage and the early fixed color stage.（6）Stepwise regression analysis showed that proteins,carotenoids and total phenols were the main chemical components that affected the yellow-turning degree of tobacco leaves during the curing process,among which proteins and carotenoids played a dominant role,and the prediction accuracy of the equation was high. |
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