The upper tobacco leaves have high concentration and sufficient aroma. With the deepening of cigarette tar reduction, the demand for upper tobacco leaves with high availability increases. Improving the usability of upper tobacco leaves is an unavoidable and important research topic in tobacco industry, which is of great significance to improve the economic benefits of tobacco leaves and the development of cigarette brands [1-2]. High nicotine content, low ratio of reducing sugar to sugar and alkali, and internal chemical composition disharmony are the main characteristics of chemical composition of upper tobacco leaves [3]. At present, there are many studies on improving the usability of upper leaves in China [4-6], and although some achievements have been made, no substantive breakthrough has been made [7]. In order to provide reference and basis for flue-cured tobacco production in Wenshan, the main chemical components of B2F tobacco in Wenshan were analyzed.
1 materials and methods
1. 1 smoke sample collection and determination
In 20 127, representative B2F tobacco leaves 20 13 were collected in Wenshan, each piece was10.5 kg, including Wenshan 19, Xichou 14, Yanshan 3 1, Qiubei 25 and Maba. The contents of nicotine, total nitrogen, total sugar, reducing sugar, potassium and chlorine were determined according to the method of Wang Ruixin et al. [8], and the derived values of nitrogen-alkali ratio, sugar-alkali ratio, potassium-chlorine ratio and other main chemical components of tobacco leaves were calculated.
1.2 data processing and analysis
The chemical component availability index (CCUI) for comprehensive evaluation of the main chemical components of upper tobacco leaves is determined by the membership function model and calculated according to the formula CCUI=, where Nij and Wij represent the membership value and weight coefficient of the I-th tobacco leaf sample and the J-th index respectively, where 0
Use IBM SPSS 20.0 software and Excel to process and analyze the data.
2 Results and analysis
2. 1 Statistical analysis of main chemical components of B2F tobacco in different districts and counties of Wenshan Prefecture
See Table 1 for the main chemical components of B2F tobacco leaves in Wenshan Prefecture. According to the chemical composition index of "international high-quality tobacco" [9], nicotine 1.5%~3.5%, total nitrogen 1.5%~3.0%, total sugar 18%~24%, reducing sugar16% ~. According to the table 1, the nicotine content of B2F tobacco leaves from Yanshan, Maguan, Qiubei and Guangnan is relatively high, with an average value above 3. 1%, and the nicotine content of some samples is above 4%, while the nicotine content of tobacco leaves from Xichou and Malipo is moderate. The average content of total sugar and reducing sugar in tobacco leaves in Qiubei is low, while the content of total sugar and reducing sugar in tobacco leaves in other districts and counties is within the appropriate range. The total nitrogen content in all districts and counties is generally within the appropriate range, the potassium content is relatively low, with an average value below 2%, and the chlorine content is generally low, with an average value below 0.3%.
2.2 Effectiveness analysis of main chemical components of B2F tobacco leaves in different districts and counties of Wenshan Prefecture
Taking the main chemical composition indexes of upper tobacco leaves as the factors to evaluate the effectiveness of chemical composition of flue-cured tobacco in different districts and counties of Wenshan Prefecture, the membership degree of each chemical composition index is calculated by using fuzzy mathematics theory, so that the original data of each evaluation "main chemical composition index" are converted into a value of 0. 1~ 1.0. There are two main types of membership functions commonly used in comprehensive evaluation of chemical composition of tobacco leaves, namely, S-type and parabolic type, in which the function types of nicotine, total nitrogen, reducing sugar, sugar-alkali ratio and nitrogen-alkali ratio are all parabolic, and the function expression is:
The availability index of chemical constituents in upper leaves of Wenshan, Yunnan Province is shown in Table 3. It can be seen from Table 3 that the availability index of chemical components in the upper leaves of Xichou is the highest, with an average value of 0.75, and the sample sizes with the availability index of 0.8~ 1 and 0.6~0.8 are 35.7 1% and 50% respectively. Validity indexes of chemical constituents in upper leaves of Malipo and Wenshan are relatively high, with the average values of 0.68 and 0.65, respectively, and the proportions with validity indexes greater than 0.6 are 66.66% and 52.63%, respectively. The availability indexes of chemical constituents in the upper leaves of Yanshan, Maguan and Guangnan are low, which are 0.5, 0.58 and 0.55 respectively. The availability index of chemical components in the upper leaves of Qiubei is the lowest, which is 0.45, and the availability index of chemical components in 84% samples is below 0.6.
3 Summary and discussion
In recent years, a lot of research has been done to improve the availability of upper leaves, especially to reduce the nicotine content of upper leaves [12- 14]. At present, the main characteristics of chemical composition in upper leaves of flue-cured tobacco in China are high nicotine content, low ratio of reducing sugar to sugar and alkali, and uncoordinated internal chemical composition [15- 16]. Statistical analysis of chemical composition showed that the nicotine content of B2F tobacco leaves from Yanshan, Maguan, Qiubei and Guangnan was higher, with an average value of more than 3. 1%, and the nicotine content of some samples was more than 4%. The average content of total sugar and reducing sugar in Qiubei tobacco leaves is low. The analysis of chemical composition validity index shows that the chemical composition validity index of the upper leaves of Yanshan, Maguan and Guangnan is low, and the chemical composition validity index of the upper leaves of Qiubei is the lowest. To sum up, the high nicotine content in upper leaves is still one of the reasons for the low utilization rate of chemical components in upper leaves, and the low content of total sugar and reducing sugar in upper leaves is also an important reason for the low utilization rate of chemical components in upper leaves of Qiubei.
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