普洱熟茶茶褐素的化学结构、形成机理与生物活性研究

The structures of polyphenols and its formation mechanisms are interesting and attractive from the viewpoints of natural product chemists. Ripe Pu-er tea as one major post-fermented tea, is increasingly attracting more and more attention and many studies have been carried out, due to the various health-giving biological function. However, as the major component in Ripe Pu-er tea, the structures and formation mechanism of theabrownin have not been understood so far. Based on our previous study on polyphenol and the research experience on black tea pigments, this project is going to study the polyphenols in theabrownin of ripe Pu-er tea with the combination of natural product chemistry, polymer chemistry and organic chemistry, to isolate, purify and further clarify their chemical compositions and structures, on the basis of various spectroscopic analysis, chemical degradation, enzymatic hydrolysis, LC-MS, and MALDI-TOF-MS analysis, and so on. Furthermore, their formation mechanism will be studied based mainly on the biotransformation study of major constituents in raw Pu-er tea with the prepondarant microbes in ripe Pu-er tea production. The polyphenols in theabrownin and biotransformation products by microbe will be evaluated for their antioxidant and anti-tumor activities, as well as the effects on diabetes. The results will not enrich the chemical and functional studies on tea and polyphenols, but provide scientific and technological support for the standardized production of ripe Pu-er tea and its wide application to health food industry, as an example of post-fermented tea.

植物多酚是天然产物研究的热点之一。普洱熟茶是后发酵茶中的主流品种，因具有多方面的生物活性和保健功能而备受关注。但决定其特殊汤色和生理功能的高聚多酚类成分即茶褐素的化学结构及形成机理至今尚不明确。本项目拟在已有多酚研究和红茶色素研究的基础上，应用传统天然产物化学与高分子化学、有机化学、菌物学和生物技术等相结合的综合技术手段与研究方法，分离纯化普洱熟茶中的茶褐素类成分，通过多种波谱，光谱，酸水解、硫醇降解等化学降解，生物酶解，以及液质、MALDI-TOF质谱分析等技术，对茶褐素类成分的化学组成进行综合分析和结构阐明。开展后发酵优势菌株对生茶中主要化学成分的生物转化，阐明普洱熟茶茶褐素的形成机理。对茶褐素及转化产物进行抗氧化、降血糖、抗肿瘤等生物活性评价，充实茶叶及多酚的化学与功能性研究内涵，为以普洱熟茶为代表的后发酵茶的深度开发利用和规范化生产提供科学依据和技术支撑。

植物多酚是天然产物研究的热点之一。普洱熟茶是后发酵茶中的主流品种，因具有多方面的生物活性和保健功能，备受关注。但决定其特殊汤色和生理功能的高聚多酚类成分即茶褐素的化学结构及形成机理至今尚不明确。本项目应用传统天然产物化学，与高分子化学、有机化学、菌物学和生物技术等相结合的综合技术手段与研究方法，对普洱熟茶中的茶褐素类成分进行了分离纯化，通过多种波谱、光谱、化学降解、以及液质、MALDI-TOF质谱分析等技术，对茶褐素类成分的化学组成进行了综合分析和结构阐明。普洱熟茶茶褐素为非均相聚合物，以黄烷-3-醇为其主要结构单元发生聚合，且多发生在C-6, C-8位，并结合有由茶氨酸由来的pyrrolidinone基团。此外，还与多糖聚合形成高分子物质，多糖部分占其结构的4.8%-23.4%，主要由常见单糖组成，分子量大于210 kDa。项目开展了普洱熟茶后发酵优势菌株对普洱生茶中主要化学成分的生物转化，并与多酚氧化酶发酵制作的红茶进行了比较研究，分离鉴定了一系列化合物，对普洱熟茶茶褐素的形成机理进行了探讨。普洱茶在高温高湿的发酵过程中，微生物大量繁殖，茶叶中的儿茶素类成分发生水解，脱去C-3位的没食子酰基，同时C-6和C-8位较为活泼，与另一分子儿茶素的C-4位发生缩合，以及与由茶氨酸由来的pyrrolidinone基团相连，并与茶叶中的多糖发生聚合。对普洱熟茶茶褐素以及分离得到的化合物进行了抗氧化、降血糖、抗肿瘤等生物活性评价，部分成分显示有较强的生物活性，为普洱熟茶在健康保健品产业的广泛应用和功能产品的进一步研发提供重要的科学依据和技术支撑，充实了茶叶及多酚化学研究的内涵。