Evaluation of Radical Scavenging and α-Glucosidase Inhibitory Effects of Gallic Acid Reactants Using Polyphenol Oxidase

Gallic acid is a representative hydroxybenzoic acid and is found in free form in several plants and in various esterified forms as a part of hydolyzable tannins. Convenient enzymatic transformation of trihydroxylated gallic acid with polyphenol oxidase originating from pear was evaluated to investigate whether polyphenol oxidase can be used as a valuable compound to improve the biological activity of gallic acid. Enzymatic oxidation processing of gallic acid using polyphenol oxidase was carried out for five different reaction times. The antioxidant effects of transformed gallic acid for different reaction times were evaluated via radical scavenging assays using 1,1-diphenyl-2-picrylhydrazyl and 2,2"-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals. In addition, the anti-diabetic property of the transformed gallic acid was measured based on α-glucosidase. Gallic acid reacted for 5 h showed significantly higher antioxidant and α-glucosidase inhibitory activities compared to the tested positive control substances. Biotransformation of simple gallic acid induced by polyphenol oxidase might be responsible for enhancing the biological activity of gallic acid.