Fermentation of Robinia pseudoacacia flower for improving the antioxidation: optimized conditions, active composition, mechanism, and biotransformation process

Abstract

Robinia pseudoacacia flower is a natural product with many biological activities, including antioxidation. To further develop its antioxidation, the extract was fermented by Aspergillus niger FFCC 3112 in the medium with carbon to nitrogen ratio of 1.4:1 and initial pH of 4.2 for 3.5 days to form the best antioxidant activity of the fermentation product by strain screening, single factor optimization, and response surface methodology. Further analysis, isolation and activity determination showed that a main chemical component, kaempferol-3-O-α-L-rhamnopyranosyl-(1→6)-β-D-galactopyranosyl-7-O-α-L-rhamnopyranoside, in the extract was completely hydrolyzed to kaempferol-7-O-α-L-rhamnopyranoside and kaempferol with better antioxidant activity through biotransformation, which was the basis for improving the antioxidant activity of fermentation products. Moreover, the mechanism of antioxidant and the contribution of phenolic hydroxyl groups were investigated by density functional theory. The result indicated that the antioxidant capacity of kaempferol-7-O-α-L-rhamnopyranoside and kaempferol increased with the increase of solvent polarity. In high-polarity solvents, they mainly scavenge free radicals through single electron transfer followed by proton transfer.

Graphical Abstract

Keywords:

• Antioxidant mechanism
• Aspergillus niger
• counter-current chromatography
• density functional theory
• kaempferol
• kaempferol-7-O-α-L-rhamnopyranoside

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by grants from Basic Research Projects of Liaoning Universities (Nos. LJKMZ20220901 and LJKMZ20221098) and National Natural Science Foundation of China (No. 22278045).