Changes Of Chemical Components During The Aging Process Of Flue-cured Tobacco And Their Relation To Aging Quality

Aging of flue-cured tobacco(Nicotiana tabacum L.) was one of the key measures to improve both the quality and the utility of tobacco.For a long time,the aging quality of flue-cured tobacco has been mainly estimated by human sensory evaluation,which existed many disadvantages including being expensive,slow and subjective.Developing a simple,rapid and objective method to judge the aging quality of tobacco is of very great significance in tobacco technology and production.Ten of chemical components,including pH,iodine value,total water soluble sugar, reduced sugar,nicotine,volatile base,total organic acid,volatile acid,total nitrogen,and starch,and four groups of aroma constituents,i.e.,the four degrading compounds of aromatic amino acid,maillard reaction,cembranenoid,and carotenoid,of flue-cured tobacco with different tobacco production areas,quality grades and aging time were analyzed in order to understand the basic rule of tobacco aging and to establish new effective chemical methods to judge the aging quality of flue-cured tobacco in the practical production.The main research contents included:(1) The changing rule of major chemical components during the aging process of flue-cured tobacco;(2) The factors influencing chemical compositions of aging flue-cured tobacco;(3) The changing rule of aroma constituents in aging flue-cured tobacco with different grades and production areas;(4) The relationship between the chemical composition and human sensory evaluation;(5) Development and application of chemical methods for evaluating aging quality of tobacco.The main results were as follows:1.In the process of aging,as the time of aging increased,there was a decreasing trend existed for pH value,total water-soluble sugar and volatile base,while an opposite occurred for iodine value,total organic acids and volatile acid.No much change was found for nicotine,total nitrogen starch content during the aging.The reduced sugar decreased in the first 9 months,then increased a little during 9-12 months,and finally decreased again afterwards due to the transformation of relating matters.2.The human sensory evaluation value increased continuously during the aging,with a rule being increasing faster in the first 24 months,then a little slower after 24 months, and finally a slightly deceasing after 30 months of aging.3.Chemical components changed greatly in the first 24 months of aging but tended to be stable with a narrow changing extent.4.pH value of flue-cured tobacco from 6 production areas was obviously different,the values ranked as,for province being Dongbei＞Yunnan＞Sichuan＞Hubei＞Guizhou＞Fujian,and for parts of the flue-cured tobacco being middle leaf＞lower leaf＞upper leaf. The change of iodine values was completely opposite to that of pH values.The content of total water soluble sugar and reduced sugar ranked as Sichuan＞Fujian＞Yunnan＞Guizhou＞Hubei＞Dongbei for the production areas,and the middle leaf＞the upper leaf＞the bottom leaf for the different parts.The nicotine and volatile alkali content in six major producing areas were Guizhou＞Hubei＞Fujian＞Yunnan＞Sichuan＞Dongbei,and the upper leaf＞the middle leaf＞the bottom leaf.The order of the organic acid content was Guizhou＞Yunnan＞Hubei＞Sichuan＞Fujian＞Dongbei,and the upper leaf＞the bottom leaf＞the middle leaf.The saturated fatty acids and fatty acids was Fujian＞Sichuan＞Guizhou＞Yunnan＞Hubei＞Dongbei.And the values of human sensory evaluation were Hubei＞Yunnan＞Sichuan＞Fujian＞Guizhou＞Dongbei,and the middle leaf＞the upper leaf＞the bottom leaf.5.A continuing increasing trend was found for the aromatic amino acid degradation compounds,the maillard reaction compounds,the cembranenoid degradation products, the carotenoid degradation products and chlorophyll degradation products of flue-cured tobacco from 6 production areas.In the first 18 months of aging the rate increased fairly fast,after 18 moths the rate of increase slowed down.With the increasing of aging time, degradation of chlorophyll content had a continuing downward trend.In six major producing areas,the content of aromatic amino acid degradation products was Fujian＞Yunnan＞Guizhou＞Hubei＞Sichuan＞Dongbei;The content of the Maillard reaction matter was:Fujian＞Yunnan＞Sichuan＞Hubei＞Guizhou＞Dongbei;the content of cembranenoid degradation products was Hubei＞Yunnan＞Sichuan＞Guizhou＞Fujian＞Dongbei;The content of the carotenoids degradation products was Fujian＞Hubei＞Guizhou＞Yunnan＞Sichuan＞Dongbei;The content of the chlorophyll degradation products was:Fujian＞Guizhou＞Hubei＞Sichuan＞Yunnan＞Dongbei. 6.Correlation analysis showed that pH value,total water soluble sugar and starch had a significantly negative correlation with the human sensory evaluation value.However, Iodine value,nicotine,the volatile base,the total organic acids,total nitrogen had a significantly positive correlation with human sensory evaluation value.7.Chemical components were closely related,pH value was negatively related to nicotine,volatile base,total organic acids and total nitrogen,but positively to iodine value,volatile acid,total water soluble sugar and reduced sugar.Iodine value related positively to pH value,total sugar and reduced sugar,and negatively to nicotine,the total organic acids and total nitrogen.The total organic acid had a very significant negative correlation with pH value,total sugar,reducing sugar and starch,and had a very significant positive correlation with the iodine value and nicotine.Volatile acid was negatively related with the pH value,and positively related with the iodine value.8.By Using of multivariate statistical analysis,the multiple regression model between the values of human sensory evaluation(Y) and 10 chemical components(x1:pH value; x2:iodine value;x3:total sugar;x4:reduced sugar;x5:nicotine;x6:volatile base;x7: total organic acid;x8:volatile acid;x9:total nitrogen;x10:starch) was established as(F =11.13,P＜0.0001):Y=96.40962-6.09084X₁+1.09281X₂-0.64631X₃+1.32682X₄-2.07649X₅+27.93830X₆+0.3 0411X₇+4.77529X₈+2.05941X₉-0.90409X₁₀.The optimal regression equation by backward regression method was(F=11.13,P＜0.0001):Y=129.17447-10.76616X₁ +0.56916X₂+25.18313X₃+5.21851X₄-0.98300X₅.9.Principal component analysis showed that 10 chemical components were extracted as 4 main principal components,which the cumulative contribution reached to 89.96%.10.A series of regression models was established to forecast(or estimate) the values of human sensory evaluation(Y):(1) the optimal pH regression model:Y= 121.84-1.3821*pH²,F=38.04,Pro.＜0.0000;or Y=-412.51233+201.31*pH-20.26861 pH²,F=49.44,Pro.＜0.0001.(2) optimal iodine value regression model:Y =I/(0.011341*I+0.00026656),F=53.16,Pro.＜0.0000.(3) the total organic acids regression model:Y=TA/(0.0089015*TA+0.004515),F=46.69,Pro＜0.0000.(4) the optimal nicotine regression model:Y=TA/(0.0099248*YJ+0.0040851),F=76.269, Pro＜0.0000.(5) the mukiple composite regression model were Y= 56.7508-0.63997*pH²+50.09304*TA-13.27179*TA²,F=19.62,Pro.＜0.000,in which the TA was total organic acids.11.The practical Using of the regression model to estimate the values of human sensory evaluation was quite successful.The results showed that the accuracy of the model forecast was up to more than 95%.