烟叶果胶糖醛酸结构的固态核磁共振波谱表征

烟叶果胶不同糖醛酸结构的含量分布，对其生理功能和产品品质有着重要影响。为表征烟叶果胶糖醛酸结构，采用固态¹³C交叉极化/魔角旋转核磁共振波谱技术(¹³C CP/MAS NMR)，以二甲基硅橡胶管为内标物质，建立烤烟烟叶中果胶含量的定量分析方法。选择NMR图谱中果胶C-6区域的波谱峰，应用PeakFit软件进行去卷积分峰处理，实现烟草样品果胶不同糖醛酸结构，即果胶酸(-COOH)、甲酯化果胶(-COOCH₃)、果胶酸钙盐(-COO^-)等定性和含量分布的分析表征。应用固态核磁共振波谱分析表征了不同部位9种烟叶样品中的果胶含量及其糖醛酸结构。结果表明，烟叶果胶含量随着烟叶部位上升而逐渐增高。样品烟叶中甲酯化果胶的含量分布均小于50%，属低甲酯化果胶。对比中部烟叶，上部叶的甲酯化果胶含量偏高，下部叶偏低，而上部叶的果胶酸钙盐含量较低，下部叶较高。结果为烟草果胶大分子结构与性能的关系研究，提供准确、简便的技术方法。

Characterization on alduronic acids structure of pectin in flue-cured tobacco using a solid-state NMR method

The content distribution of pectin alduronic acids structure in tobacco leaves has an important impact on its physiological function and product quality. A quantitative analysis method was developed for characterizing the alduronic acids structure of pectin in Flue-cured tobacco samples by solid state ¹³C CP/MAS NMR, using dimethyl silicone rubber tube as the internal standard substance. The C-6 carbon region of pectin in the NMR spectrum was selected, and the deconvolution of spectral peaks was performed using the PeakFit software to achieve the qualitative and quantitative analysis of different alduronic acid unit structures of pectin in tobacco samples, such as carboxylic acid group (-COOH), methyl ester group (-COOCH₃) or carboxylate anion group(-COO^-). The results, applied to the measurement of pectin content and the structural characterization of the alduronic acid units in nine tobacco samples from different parts of the tobacco leaf, showed that the pectin content of the tobacco leaf increased gradually with the rise of the tobacco parts. The distribution of methylated pectin content in the sample tobacco leaves was less than 50%, which was low methylated pectin. In contrast to the central tobacco leaves, the upper leaves showed high methylated pectin content, while the lower leaves showed high calcium pectate content. The result provides an accurate and simple technical method for the study of the relationship between the structure and properties of tobacco pectin macromolecules.