Abstract: Objective: This paper describes the effect of biotransformation by Lacbacillus perolens B2 on the flavonoid composition and antioxidant activities of Ginkgo biloba pollen. Methods: The yields and high performance liquid chromatography of the ethanol extracts of G. biloba pollen and its bioconverted products and their fractions in petroleum ether, ethyl acetate and n-butanol phases were analyzed, and their in vitro antioxidant activities were evaluated by 2-2’-azino-bis-(3-ethyl-benzthiazoline-6-sulfonic acid) and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activities. By the protective effect on H2O2-induced injury in RAW264.7 mouse macrophages, their cellular antioxidant activities were also evaluated. Results: After bioconversion by L. perolens B2, the yields of all the extract and fractions were increased. The main flavonoid glycosides of G. biloba pollen were transformed into flavone aglycones such as kaempferol, enriched in the ethyl acetate phase. The in vitro antioxidant activities were improved as well, and the ethyl acetate extractable fraction of the biotransformation products showed the highest in vitro antioxidant activity. Cell experiments showed that the extracts of G. biloba pollen and its biotransformation products and their ethyl acetate soluble fractions could alleviate H2O2- induced apoptosis in RAW264.7 cells in a dose-dependent manner. The biotransformed extract and its ethyl acetate soluble fraction had stronger ability to protect RAW264.7 macrophages from H2O2-induced damage than their native counterparts. The biotransformed ethyl acetate soluble fraction had the highest protective ability, and it could completely protect RAW264.7 macrophages from H2O2-induced damage at a concentration of 15 μg/mL. Conclusion: L. perolens B2 can biotransform the major flavonoid glycosides of G. biloba pollen into flavone aglycones such as kaempferol and significantly improve the yields, in vitro antioxidant activities and protection against H2O2-induced injury in RAW264.7 macrophages of the crude extract and its fractions in various organic solvents (P < 0.05). The biotransformed ethyl acetate soluble fraction has the highest antioxidant activity.

Key words: Ginkgo biloba pollen, Lacbacillus perolens B2, flavonoids, biotransformation products, in vitro antioxidant activity, cellular antioxidant activity