Bioconversion of tea polyphenols to bioactive theabrownins by Aspergillus fumigatus

Theabrownins (TB) are water-soluble phenolic compounds associated with the various health benefits of Pu-erh tea, a post-fermented Chinese dark tea. This work reports on the production of theabrownins from infusions of sun-dried green tea leaves using a pure culture of Aspergillus fumigatus isolated from a solid-state Pu-erh tea fermentation. A theabrownins yield of 158 g kg(-1) sun-dried green tea leaves was obtained in 6 days at 45 °C in an aerobic fermentation. In a 2 l fermenter, the yield of theabrownins was 151 g kg(-1) sun-dried green tea leaves in 48 h of aerobic culture (45 °C, 1 vvm aeration rate, 250 rpm agitation speed). Extracellular polyphenol oxidase and peroxidase of A. fumigatus contributed to this bioconversion. Repeated batch fermentation process was used for producing theabrownins but was less productive than the batch process.