普洱茶及其原料多糖分子组成及光谱学特性研究

研究了普洱茶发酵过程中多糖分子组成及光谱学特性的变化规律。结果显示，普洱茶及其原料多糖主要组分TPS1和TPS2的分子组成及光谱学特性差异显著。TPS2含有较高糖醛酸，而TPS1含有较高的中性糖和蛋白质。TPS1和TPS2均由半乳糖(Gal)、阿拉伯糖(Arb)、甘露糖(Man)、葡萄糖(Glu)、木糖(Xyl)、鼠李糖(Rha)六种单糖组成，其分子摩尔比分别为23.6∶5.9∶24.2∶1.1∶1.8∶3.2和26.9∶3.2∶19.3∶5.5∶1.3∶2.7。TPS2和TPS1的重均分子量分别为1.68×104和1.21×104道尔顿。TPS1和TPS2水溶液在200～400 nm之间无特征吸收峰。红外光谱图显示，TPS1和TPS2的信息基本相同，都是含有吡喃环的多糖。在三维AFM图中，TPS1形成的聚集体高度约为4 nm, 长宽约为0.2～0.4 μm，TPS2形成的聚集体高度约为40 nm，长宽约为0.5～0.8 μm。SEM图片显示，TPS1呈表面光滑的鳞片状聚集体，TPS2呈表面粗糙的片状聚集体。引起普洱茶及其原料多糖分子组成及光谱学性质发生变化的动力主要为微生物作用和湿热作用。

The Molecular Composition and Spectral Properties of Polysaccharide Isolated from Pu-Erh Tea and Its Material

Pu-erh tea, a kind of well-known tea from the ancient time, is originally produced in the Yunnan Lanchan River basin through a special solid state fermentation by fungi. It uses sun-dried green tea as its starting materials. To investigate the variation of composition and spectral properties of polysaccharide during solid state fermentation of pu-erh tea by using Saccharomyces cerevisiae as preponderant starter and using sun-dried green tea as materials in the present study. The results showed that the content of water soluble polysaccharide was increased，and the activity of hydrolase such as cellulase，pectinase and glucomylase were also enhanced. The content of neutral sugar increased with the ferment time increasing and the M_W of raw polysaccharide showed significant difference during fermentation. The main polysaccharide TPS2 and TPS1 were isolated and purified from pu-erh tea and its materials by DEAE-52 and Sephadex G-150 column chromatography. TPS2 contains the higher content of uronic acid, but TPS1 contains the higher contents of neutral sugar and protein. Monosaccharide analysis by GC-MS revealed that TPS1 and TPS2 were composed of arabinose, galactose, glucose, rhamnose, xylose and mannose with molar ratios of 24.2∶23.6∶5.9∶3.2∶1.8∶1.1 and 19.3∶26.9∶3.2∶2.7∶1.3∶5.5, respectively. The average molecular weight of TPS1 and TPS2 was 1.68×104 and 1.21×104 Daltons, respectively. UV scanning spectrum showed that TPS1 and TPS2 had no characteristic absorption between 200 and 400 nm wavelength, it suggested that they contain trace protein. IR spectrum of TPS1 and TPS2 demonstrated that pyranoid rings were contained in them. As shown in the image of atomic force microscope, the molecular appearance of TPS1 and TPS2 resembled islands and apparently consisted of conglomerations. The height of conglomerations of TPS2 was about 40nm and the length or width was 0.5-0.8 μm, while the height of conglomerations of TPS1 was about 4nm and the length or width was 0.2-0.4 μm. TPS2 shows sheet conglomerations with rough surface, but TPS1 shows squama conglomerations with smooth surface in the image of scanning electron micrograph. The experimental data suggested that the variation of composition and spectral properties of polysaccharide isolated from pu-erh tea and its materials owed to the action of microorganism and humid and thermal action for long time process.