Objective

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To explore the chemical composition changes of Wubeizi before and after vinegar processing by liquid chromatography-mass spectrometry （LC-MS）， and the mechanism of vinegar processing of Wubeizi from the perspective of antioxidation.

Methods

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LC-MS was used to compare the chemical composition characterization of water extract of Wubeizi before and after vinegar processing. The antioxidant capacity was determined by iron ion reducing energy test （FRAP）， DPPH free radical scavenging capacity test and ABTS free radical scavenging capacity test.

Results

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The ability of ferric ion reduction， the free radical scavenging ability of DPPH and the scavenging ability of ABTS of vinegar-processed Wubeizi were higher than those of Wubeizi and ascorbic acid with same concentration. That is， the iron ion reducing ability IC50， DPPH free radical scavenging ability IC50 and ABTS scavenging ability IC50 of the aqueous extract of Wubeizi processed with vinegar were superior to those of ascorbic acid with the same concentration of 29.17%， 61.47% and 39.40% respectively. 53 compounds， including gallic acid， ellagic acid， mono-O-gallic acid acyl glucose to dodeca-O-gallic acid acyl glucose， gallic acid with different polymerization degrees to quintuple gallic acid and their isomers， were identified by liquid chromatography-mass spectrometry combined with UNIFI analysis platform. The comparative analysis showed that the content of polygalactose above 5-O-gallic acid after vinegar processing was lower than that before vinegar processing， and the content of polygalactose was different. After vinegar processing， the contents of quintuple gallic acid and tetraploid gallic acid with high polymerization degree in gallic acid polymer decreased； double gallic acid， ellagic acid and gallic acid were higher than those before vinegar processing.

Conclusion

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Vinegar processing has a mild hydrolysis effect on tannins of Wubeizi， which partially hydrolyzes macromolecular gallic acid esters and produces free gallic acid monomers and oligomers， exposing more active phenolic hydroxyl groups so as to enhance the antioxidant effect.