Inhibition Kinetics of Polyphenol Oxidase from Purple Sweet Potato by Ascorbic Acid

Abstract

With catechol as a substrate, some kinetic parameters, including Michaelis constant (Km), maximum reaction velocity (Vmax) and substrate inhibition constant (KI) for the reaction catalyzed by polyphenol oxidase (PPO) from purple sweet potato (PSP) were mainly studied here by spectrophotometry. Kmand Vmaxwere determined depending on bi-reciprocal diagram of Lineweaver-Burk and Hanes-Woolf diagram respectively, with Kmof 12.06 mM and Vmaxof 43.66 mM·min. The effects of four various inhibitors on PPO activity were different. Ascorbic acid (AA) and phytic acid (PA) showed strong inhibitory effects, with AA of the highest effect and citric acid (CA) the lowest. Among these inhibitors, AA was a reversible competitive inhibitor with KIof 15.26 mM, which was significant and instructive to the quality and benefit improvement of processed PSP products.