Structural Characterization and Gut Microbiota Modulation of Theabrownins Prepared by Macroporous Resin AB-8 Combined With Ultrafiltration Fractionation.

This study developed an efficient and environmentally benign method using macroporous resin purification combined with ultrafiltration fractionation to prepare a high-molecular-weight theabrownin fraction (TBSP5, Mw > 100 kDa) from summer green tea fermented with Aspergillus cristatus (MK346334). TBSP5 exhibited higher purity than theabrownins obtained via conventional organic solvent extraction (TBSE) while it retained comparable structural characteristics. Both TBSP5 and TBSE showed substantial stability under simulated upper gastrointestinal digestion, undergoing only limited hydrolysis before reaching the colon. Subsequent in vitro anaerobic fermentation showed that, compared with TBSE, TBSP5 more effectively promoted the production of short-chain fatty acids, particularly acetic and propionic acids. This microbial response was accompanied by a significant increase in the relative abundance of beneficial bacteria, particularly Bifidobacterium longum and B. pseudocatenulatum. These findings establish a novel green preparation strategy for theabrownins and support the prebiotic potential of theabrownins for modulating gut microbiota composition. PRACTICAL APPLICATIONS: The macroporous resin purification method developed in this study offers a green, efficient and scalable approach for producing high-purity theabrownin fractions - TBSP5 (>100 kDa) from fermented summer green tea. The TBSP5 fraction exhibits promising prebiotic potential by selectively enriching beneficial Bifidobacterium species and promoting short-chain fatty acid production, supporting its potential application as a functional food ingredient or dietary supplement for gut health promotion.