Abstract: This study aimed to efficiently prepare oligosaccharides from large-leaf yellow tea and systematically elucidate their structural characteristics and biological activities. A mixture of cellulase and pectinase was used for targeted enzymatic hydrolysis of large-leaf yellow tea. The process parameters were optimized by the combined use of single-factor experiments and response surface methodology with Box-Behnken design. The obtained oligosaccharide (ELYPW) was structurally characterized by high performance gel permeation chromatography (HPGPC), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM). Its hypoglycemic, hypolipidemic, and gut microbiota-modulating effects were evaluated in a high-fat diet-induced obese mouse model. The results revealed that the optimal preparation conditions for ELYPW were as follows: a cellulose-to-pectinase ratio of 1:2, an enzyme concentration of 0.8 mg/mL, pH 5.0, hydrolysis temperature of 40 ℃, and a hydrolysis time of 4 h. Structural characterization indicated that ELYPW had a molecular mass of 3.2 × 103 Da; it was composed primarily of rhamnose, galacturonic acid, glucose, galactose, and arabinose at a molar ratio of 9.32:39.17:1.00:23.11:25.34, with an average particle size of 52.56 nm. In vivo experiments demonstrated that ELYPW significantly reduced body mass, fat mass, fasting blood glucose levels, and serum concentrations of total cholesterol, triglyceride, and low-density lipoprotein cholesterol in obese mice, while concurrently elevating serum high-density lipoprotein cholesterol levels and alleviating hepatic lipid accumulation. Furthermore, gut microbiota profiling showed that ELYPW ameliorated intestinal flora dysbiosis in obese mice, markedly increasing the abundances of beneficial bacterial taxa including Akkermansia, Bifidobacterium, and Lachnospiraceae_NK4A136_group, and decreasing the abundances of detrimental taxa such as Romboutsia, unclassified_f__Atopobiaceae, and Corynebacterium. Collectively, this study demonstrates that ELYPW exhibits prominent effects in ameliorating glycolipid metabolism disorders as well as regulating the gut microbiota. This finding provides theoretical support for the development and application of tea-derived functional oligosaccharides, and offers new insights for the high-value utilization of tea resources and the design of functional foods against metabolic syndrome.

Key words: large-leaf yellow tea oligosaccharides; enzymatic hydrolysis; structural characterization; glycolipid metabolism; gut microbiota