| Tobacco(Nicotiana tabacum L.), an important agricultural crop, is widely planted in China. Altitude, sun exposure and temperature are different and quality of tobacco leaves differs considerably among typical production regions. The chemical components of tobacco leaves, particularly the aroma components produced during metabolism, are closely associated with the flavor and quality of cigarettes, whereas the ecological conditions, particularly climatic conditions, affect the degradation process and the content of degradation products. It is very important to study on the key indices of aroma components from typical production regions and climatic factors.Aroma components in tobacco leaf samples collected from typical production regions were analyzed using solvent extraction and liquid chromatography-gas chromatography-mass spectrometry(LC-GC-MS). Principal component analysis(PCA) was applied to obtain the key indices of aroma compounds in flue-cured tobacco leaves. Typical production regions were classified and identification models of partial least squares-discrimination analysis(PLS-DA) were established according to the content of aroma components. Combined with analysis of climatic factors in different growth stages of flue-cured tobacco, the correlation between climatic factors and aroma components were studied.The main results were as follows:(1) The observed aroma components were significantly different among typical production regions. The PCA showed that megastigmatrienone, 3-oxo-α-ionol, neophytadiene, farnesylacetone, solanone and norsolandione were the key indices of aroma components. The characteristics of aroma components in different production regions reflected the lower content of plastid pigment and cembratriendiol catabolites and embratriendiol catabolites in Guizhou and Taining in southeast production regions, the moderate content of solanone and norsolandione in Shandong, Henan and Wannan production regions, the higher content of neophytadiene in Wuling and Qinba production regions, the higher content of solanone, norsolandione, geranylacetone and β-Ionone in Xiangnan production regions, the higher content of ionone oxide and dihydroactinidiolide and the lower content of megastigmatrienone in Northeast production regions, the lower content of β-damascenone, 3-oxo-α-ionol, neophytadiene and farnesylacetone in Yunnan production regions, moreover, the higher content of plastid pigment and cembratriendiol catabolites in Yongding in southeast production regions.(2) The observed aroma components were significantly different between at least two of medium-flavor types regions, reflecting significant differences between the ecological factors in these regions. β-ionone, megastigmatrienone, farnesylacetone, solanone and norsolandione were the key indices of aroma components. The characteristics of aroma components in different ecological regions reflected the higher content of megastigmatrienone, β-damascone, β-ionone, 3-oxo-α-ionol, neophytadiene and farnesylacetone in Wuling and Qinba production regions, the higher content of 3-hydroxysolavetivone in Qinba production regions, the higher content of geranylacetone and 3-hydroxy-β-damascone in Wuling and Shandong production regions, the higher content of solanone and norsolandione in Shandong and Qinba production regions, more β-damascenone in Guizhou production regions, and the higher content of dihydroactinolide in Northeast production regions. The PCA score plot showed that samples of Guizhou production regions were clearly different from those of other regions. Collections were separated into five groups according to the different geographical origins of the tobacco samples. Interestingly, some intersections among different production regions, particularly between samples of Wuling and Qinba production regions, were observed. The scatterplots of Wuling and Qinba production regions multipoint samples overlapped, likely reflecting the similar ecological conditions.(3) Geranylacetone and farnesylacetone were significantly different among three mainly varieties in Guizhou production regions. The significant differences between leaf positions and among regions exceeded those amonge varieties. The PCA showed that megastigmatrienone, solanone and norsolandione were the key indices of aroma components. Collections were separated into three categories according to the different aroma components in tobacco samples. The first categories included Dejiang, Xingren, Xixiu, Daozhen and Weining regions with lower content of aroma components. The second one included Guiding, Kaili, Kaiyang and Yuqing regions with higher content of geranyl acetone, megastigmatrienone, 3-hydroxy-β-damascone, neophytadiene and farnesylacetone. In addition, the third one was Panxian regions with higher content of solanone and norsolandione. The PCA score plot showed that samples of Guizhou production regions were clearly separated according to the different geographical origins of the tobacco samples. The tobacco samples in Xingren regions were concentrated as well as Kaili regions, but dispersed distribution in Weining regions.(4) By using research methods of metabonomics, PLS-DA models were established to discriminate different production regions.The results of typical production regions showed that the aroma components were clearly dependent on ecological conditions, a PLS-DA model was established to discriminate seven different classes, including Guizhou and Taining in southeast production regions, Wuling and Qinba production regions, Shandong, Henan and Wannan production regions, Xiangnan production regions, Northeast production regions, Yunnan production regions and Yongding in southeast production regions. Combining the variable importance in the projection(VIP) values in the loading plot, eight aroma components with VIP values higher than 1 were selected as key aroma components. These key aroma components included neophytadiene, dihydroactinidiolide, β-damascenone, ionone oxide, 3-hydroxy-β-damascone, β-ionone, geranyl acetone and megastigmatrienone 1.The results of medium-flavor types regions showed that the aroma components were clearly dependent on ecological conditions, discriminated as five ecological regions through a multistep PLS-DA. To understand the differences among tobacco leaves in the three larger regions, including Guizhou production regions(GZ), Wuling and Qinba mountainous areas(WL-QB), Shandong and Northeast production regions(SD-NE), a PLS-DA model was established. Eight aroma components were selected as key aroma components in this model. These key aroma components included geranyl acetone, megastigmatrienone(1, 2, 4), 3-hydroxy-β-damascone, neophytadiene, β-ionone and norsolandione. Two other additional PLS-DA models were established to further understand the differences between the tobacco leaves of the WL and QB and SD and NE ecological regions. Seven aroma components were selected as key aroma components in PLS-DA models of WL and QB. These key aroma components mainly included β-damascone, β-damascenone, farnesyl acetone, 3-hydroxy-β-damascone, megastigmatrienone 3, 3-hydroxysolavetivone and solanone. Moreover, nine aroma components were selected as key aroma components in PLS-DA models of SD and NE. These key aroma components mainly included 3-hydroxy-β-damascone, megastigmatrienone, ionone oxide, farnesyl acetone, neophytadiene and dihydroactinolide.The results of Guizhou production regions showed that the aroma components were clearly dependent on ecological conditions, a PLS-DA model was established to discriminate three different classes, including Dejiang, Xingren, Xixiu, Daozhen and Weining regions, Guiding, Kaili, Kaiyang and Yuqing regions and Panxian regions. Eight aroma components were selected as key aroma components in this model. These key aroma components mainly included 3-hydroxysolavetivone, β-damascone, megastigmatrienone, solanone and farnesyl acetone.(5) The results of the simple correlation analysis and canonical correlation analysis(CCA) confirmed that climatic factors significantly affect the content of aroma components.The results of typical production regions confirmed that the relative humidity at the glomeration stages has positive effects on the content of neophytadiene, while the sunshine hours at the glomeration stages has negative effects on the content of neophytadiene.The results of medium-flavor types regions confirmed that the content of β-ionone was primarily affected by the relative humidity at the flowering stages, and the rainfall and sunshine hours at the glomeration stages. The geranyl acetone and 3-hydroxy-β-damascone contents were primarily affected by the rainfall at the flowering stages, and by the relative humidity and average temperature at the glomeration stages. Moreover, megastigmatrienone and farnesyl acetone contents were closely associated with temperature and humidity during later growth periods.The results of Guizhou production regions confirmed that the average temperature at the flowering and mature stages have positive effects on the content of megastigmatrienone and neophytadiene. The rainfall at the mature stages has negative effects on the content of solanone and norsolanadione. In addition, the relative humidity at the mature stages and the average temperature at the flowering have negative effects on the content of 3-hydroxy-β-damascone. |
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