Antioxidant and alpha-glucosidase inhibitory activities of flavonoids isolated from fermented leaves of <i>Camellia chrysantha</i> (Hu) Tuyama

Abstract Objectives Microbial fermentation has long been known as a method for processing teas to raise products with novel biological activities. Our study aimed to chemically characterize flavonoid components in fungal mediated biotransformed Camellia chrysantha (Hu) Tuyama leaves. Methods The fermented leaves of Camellia chrysantha were prepared by inoculation with an Eurotium cristatum fungal consortium and extracted with ethanol combining ultrasound-assisted technique, before introducing to chemical characterization. Normal and reverse phase C18 column chromatography and thin layer chromatography were applied for fractionation and isolation of compounds from the ethanolic extract. Nuclear magnetic resonance spectra ( 1 H NMR, 13 C NMR, HSQC and HMBC) were recorded for structure determination, while in vitro bioassays of free radical scavenging capacity and α -glucosidase inhibition were employed to assess anti-oxidative and anti-diabetic properties of isolated compounds. Results Four flavonoids, i.e. quercitrin ( 1 ), afzelin ( 2 ), (-)-epicatechin ( 3 ), and engelitin ( 4 ) were isolated from fermented Camellia chrysantha (Hu) Tuyama leaves. Compounds 1 and 3 were found to exhibit scavenging property against both DPPH and ABTS. Compound 2 was noticeably the most effective against α -glucosidase, presenting an IC 50 of 78.25 μg/mL. Conclusions The investigation on chemical composition of microbial fermented leaves of Camellia chrysantha (Hu) Tuyama brought out flavonoid compounds with significant biological activities, which could serve as a basis for further possible application in manufacturing health protecting natural products.