FTIR结合曲线拟合分析用于普洱熟茶陈化过程的研究

为了研究陈化时间对普洱熟茶所含化学成分的影响，分析了同一品种普洱熟茶在不同陈化时间的傅里叶变换红外光谱，光谱初步显示不同陈化时间的普洱熟茶的化学成分存在差异。茶叶是一个复杂的体系，其红外光谱由所含成分的特征吸收带叠加而成。为了深入探索发生变化的特征带，对光谱中的1 900～900 cm-1吸收带进行傅里叶自去卷积，确定该范围内叠加子峰的个数和预估波数位置，然后进行曲线拟合分析。通过曲线拟合分析确定不同陈化时间普洱熟茶红外光谱中的蛋白质、茶多酚、果胶和多聚糖的子峰位置。蛋白质的特征吸收酰胺Ⅱ带子峰出现在1 520 cm-1，茶多酚和果胶吸收子峰分别出现在1 278和1 103 cm-1，葡甘露聚糖和阿拉伯聚糖的吸收子峰波数是1 063和1 037 cm-1，分别利用这些子峰面积和叠加带面积的比例间接反映蛋白质、茶多酚、果胶和多聚糖的含量在陈化过程中的变化情况。曲线拟合结果显示，随着陈化时间的增加，茶叶中的酰胺Ⅱ带子峰面积比例先增大后减小，同时茶多酚和果胶类物质含量比例减少，可溶性多聚糖类物质含量比例增加。这解释了普洱熟茶随着陈化时间增加其苦涩味减弱，口感上出现甜味的原因。研究表明傅里叶变换红外光谱结合曲线拟合分析能反映普洱熟茶陈化过程中化学成分的变化，为其品质的评定提供有效依据。

Aging Process of Puer Black Tea Studied by FTIR Spectroscopy Combined with Curve-Fitting Analysis

For better determination of the chemical components in the Puer black tea, Fourier transform infrared spectroscopy was used for obtaining vibrational spectra of Puer black tea at different aging time. Fourier transform infrared (FTIR) spectra indicated that the chemical components had change in Puer black tea at different aging time. The leaf of Puer black tea was a complex system, its Fourier transform infrared spectrum showed a total overlap of each absorption spectrum of various components. Each band represented an overall overlap of some characteristic absorption peaks of functional groups in the Puer black tea. In order to explore the change of characteristic absorption peaks of functional groups with aging time, the prediction positions and the number of second peaks in the range of 1 900～900 cm-1 were determined by Fourier self-deconvolution at first, and later the curve fitting analysis was performed in this overlap band. At different aging time of Puer black tea, the wave number of second peaks of amide Ⅱ, tea polyphenol, pectin and polysaccharides at overlap band were assigned by curve fitting analysis. The second peak at 1 520 cm-1 was characteristic absorption band of amide Ⅱ, the second peaks of tea polyphenol and pectin appeared at 1 278 and 1 103 cm-1 respectively. Two second peaks at 1 063 and 1 037 cm-1, corresponds mainly to glucomannan and arabinan. The relative area of these second peaks could be indicated the content of protein, tea polyphenol, pectin and polysaccharides in the Puer black tea. The results of curve fitting analysis showed that the relative area of amide Ⅱ was increasing first and then decreasing, it indicated the change of protein in Puer black tea. At the same time, the content of tea polyphenol and pectin were decreased with the increase of aging time, but the glucomannan and arabinan were increased in reverse. It explained that the bitter taste was become weak and a sweet taste appeared in the tea with the increase of aging time. The present study suggested that Fourier transform infrared spectroscopy combined with curve-fitting analysis could reveal the biochemical changed of Puer black tea with the increase of aging time, and it was evidence for evaluation the quality of Puer black tea.