Impact of fermentation on the structure and antioxidant activity of selective phenolic compounds

The impact of fermentation on the structure and antioxidant potential of phenolic compounds in foods have received wide attention. In this study, five common phenolic compounds (ferulic acid, polydatin, cyanidin-3-O-glucoside, rutin, tannic acid) were fermented by Aspergillus oryzae, Lactobacillus plantarum and Saccharomyces cerevisiae respectively. The qualitative and quantitative analyses of the fermentation products were separately performed by HPLC-DAD-ESI-QTOF-MS/MS and HPLC-DAD, and the antioxidant properties (assessed by DPPH and ABTS assays) were also estimated. The results demonstrated that the glycosidic bonds in the phenolic compounds were hydrolyzed during fermentation, which led to the formation of additional phenolic metabolites such as gallic acid, protocatechuic acid and quercetin, as evidenced by the identification of 15 phenolic compounds in the fermented samples. The contents of these phenolics were considerably decreased (p < 0.05) to 1.72%–97.99% during fermentation, while the phenolic metabolites were detected in certain amounts (0.44–15.53 mg/L). The antioxidant activities of these phenolics also varied among different fermenting microorganisms. This study provides direct evidence of the metabolites and antioxidant properties of these common food phenolic compounds after fermentation.