Effects Of Related Factors Of Bulk Curing On Quality Of Upper Flue-cured Tobacco Leaves

To improve quality of upper flue-cured tobacco leaves, the experiment wasconducted on the Yunnan Chuxiong, Chongqing Wulong, Guizhou Suiyang, Anhui Wannan,Henan Xuchang, Hunan Chenzhou, Sichuan Liangshan and Guizhou Zunyi, during2010-2011. Effects of holding temperature time, humidity, heating rate, fan speed duringbulk curing on appearance quality, content of chemical components and their harmony,content of aroma components, smoking quality, economic characters and bulk curing timeson flue-cured tobacco leaves （B2F）. The results were as following:1. Effects of holding temperature times during bulk curing on the aroma quality ofupper flue-cured tobacco leaves. Properly prolonging holding temperature times was helpfulto increase the contents of petroleum ether extracts in upper leaves. When the time was12hat42℃and12h at54℃, the upper leaves had the highest contents of products of totalaroma components, browning reaction, cembrenoid, degraded carotenoid, andneophytadiene, furthermore, it remarkably increased content of megastigmatrienones. Andthe contents of nicotine and starch were remarkably reduced, while contents of reducingsugar and total sugar were increased, total sugar/nicotine and total nitrogen/nicotine werekept in order. It scored the highest in sensory evaluation. Holding temperature time of12hat42℃and54℃respectively could improve the harmony of chemical components, andremarkably improve aroma quality and usability of upper flue-cured tobacco leaves.2. Effects of temperature and humility on the appearance quality and internal quality ofupper leaves in flue-cured tobacco in stem-drying stage during bulk curing. the temperatureand humility in stem-drying stage had an important influence on the formation ofappearance quality and internal quality of upper leaves. Properly increase humility in thelater stem drying stage （after60℃） could greatly improve the quality of upper leaves, andthe study proved B3（dry bulb temperature54℃⁵9.9℃, wet bulb temperature38℃;dry bulb temperature60℃and after, wet bulb temperature41℃） treatment obviouslyimprove appearance quality, chemical components harmony and smoking quality, andsignificantly increase the content of main aroma components. B3treatment also had thecharacteristics of preferable note, adequate aroma amount, clean aroma quality, littleirritation, moderate density and strenth, less offensive taste and good taste. To a certaindegree, B3treatment improved the availability of upper leaves.3. Effects of heating rate during leaf-drying stage of bulk curing on smoking quality ofupper flue-cured tobacco leaf. As heating rate decreased, contents of total sugar and reducing sugar in cured tobacco gradually increased, while contents of total nitrogen,nicotine, and starch took on descending trends. Fast heating rate disadvantaged kinds ofreactions happened in cells and thus led to the decline of aroma components content andchemical compounds harmony; proper increase of heating rate could significantly increasecontents of aroma components, and improve harmony of chemical compounds of upper leaf,it had the best effect on the improvement of aroma volume, aroma quality, irritation andtaste. In conclusion, heating rate combination of1℃/3h at earlier period and1℃/2h atlater period of leaf-drying stage could remarkably improve smoking quality of upper leaf.4. Effects of fan speed during leaf drying and stem drying stage of bulk curing on theappearance quality and internal quality of upper leaves in flue-cured tobacco. the fan speedof bulk curing had an important influence on the formation of appearance quality andinternal quality of upper leaves. Properly reducing fan speed could greatly improve thequality of upper flue-cured tobacco leaves, and in the study, D3(dry bulb temperature42℃^<47℃, fan speed was1440r min^-1;47℃^<60℃,960r·min^-1，60℃⁶8℃,720r·min^-1) treatment obviously improved appearance quality, chemical componentsharmony and smoking quality, and significantly increased the content of most of aromacomponents. Upper leaves from D3had the characteristics of preferable note, adequatearoma amount, clean aroma quality, little irritation, moderate density and strength, lessoffensive taste and good taste. To a certain degree, D3treatment improved the availabilityof upper leaves.5. Effect of optimized curing technique on upper leaves quality: Based on averagecomprehensive scores on appearance quality of upper leaves in5areas, optimized techniquewas much better than CK. It showed that all of the colour, maturation, leaf structure, identityand chroma of upper leaves were improved, but oil was decreased to CK. There was nodifference between the two curing techniques on content of nicotine, total sugar, reducingsugar, total nitrogen, potassium, starch, petroleum ether extract. And among these qualityindexes, little difference existed. Compared with CK, optimized curing technique wasbeneficial to degradation of chlorophyll and carotenoid in upper leaves. The degradation inHunan Chenzhou was much bigger. Optimized curing technique had positive effect onsmoking quality of upper leaves. Compared with CK, aroma quality, volume of aroma,offensive taste, strength and aftertaste were improved obviously, but irritation decreased.The time of conventional curing technique was shorter than optimized curing technique.Internal substances in leaves could transfer completely during yellowing stage and leafdrying stage by using optimized curing technique, internal quality and economic characters has been improved. Besides, rate of high class leaf increased to15.59%compared to CK,while rate of bad leaf decreased to12.99%to CK.