| Physical and physiological biochemical characteristics of cured tobacco leaves had changed greatly during the tobacco curing stage, especially during the yellowing stage of tobacco curing. The physical change includes that the tobacco leaves were exsiccated gradually due to continual evaporation of water in leaf tissue. While the biochemical change during the cured process was much complex, which includes the disaggregation, transition and digestion of the fresh tobacco leaf cell, as well as the small molecule organic matter which formed continuously via the affecting of respiratory enzymes, hydrolytic enzymes and oxidation enzymes. It was very important for the improvement of the cured tobacco leaf quality to study deeply the regularity of the physiological and biochemical change in tobacco leaf during the curing process. In this research, The effect of different temperature and relative humidity combination on the quality of cured tobacco leaf during the yellow stage was studied, using the middle part of the tobacco leaves of Guiyan 4, which was popularized in Chongqing, as the material, with the perfect design of two factor regression, and the main results of the research were as follows:1. At the yellowing stage of curing process, the tobacco leaves could be turned yellow on the condition with as a temperature of 32.0□~42.0□ and relative humidity (RH) of 75.0%~95.0%. However, leaves quality was different with the different of temperature and RH. With the increase of the temperature, the change of the tobacco quality was like a parabola, and the effect of the temperature was larger than that of RH. The quality of cured tobacco leaves were good for that produced from the process with the environmental temperature of 36.7□~39.0□ and RH of 84.3%~91.7%, among them the best one was obtained from the temperature of 38.0□ and RH of 87.7%. The qualities of tobacco leaves descended rapidly on the condition of lower temperature (32.0□~34.5□) and RH(75.0%~80.0%) or higher temperature (39.5□~42.0□) and RH (90.0%-95.0%) , it indicated that extreme temperature and RH was unsuitable for the improvement of tobacco leaves quality.2. At the yellowing stage of the curing process, the content of substance extracted from petroleum ether was affected greatly by the temperature and RH, in which the effectof temperature was much greater than that of RH. The interaction effect of temperature and RH was also significant. Petroleum ether extract content was increased at the beginning of the curing process, then decreased with the increase of the temperature and RH. At the temperature of 36.6D~38.6D and RH of 85.4%~92.9%, the petroleum ether extract content arrived to a higher level and a high flat roof was appeared. When the temperature was 37.7D and was 87.0%, the best treatment combination of the experiment, the petroleum ether extract content was as high as reached 8.3%3. At the yellowing stage of curing process, the flavor and smoking quality of the cured tobacco leaves was influenced significantly by different temperature and RH during the curing process. The flavor and smoking quality of the cured tobacco leaves, with a total score of 60, was increased with the increase of the temperature and RH in a certain range, but high temperature of curing process can not led to the best smoking quality. The effect of temperature on flavor and smoking quality of cured tobacco leaves was also greater than that of RH, and the interaction effect between temperature and RH was significant as well. The favor and smoking quality of cured tobacco leaves was good when the temperature of curing process was 37.7D~39.0D and RH was 86.7%~92.9%, i.e. the difference of temperature between dry ball and wet ball was about 1.5D-2.5D, the flavor and smoking quality score was 48.7-49.3. The best combination of the temperature and RH during the curing process was 37.7°C+87.0%..In summary, as the results of this experiment, concerned the synchronous improvement of the favor and smoking quality and curing process, it is suggested that the temperature of curing process of tobacco leaves for Guiyan 4 should be controlled from 37.0D to 38.5D, and the relative humidity should be controlled in 86.0%~88.0%, i.e. the difference of the temperature between dry ball and wet ball was about 2.0D.
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