Inhibitors Of Potato Polyphenol Oxidase Mechanism Of Action And Color Protection In Potato Tuber Slices

Polyphenol oxidase (EC 1.14.18.1) is a copper-containing enzyme that is widely distributed in microorganisms, animals and plants. Our research in this present paper is composed of two parts. In the first part, we isolated and partially purified polyphenol oxidase from potato. The effects of tannic acid, gallic acid, L-Cysteine, 4-hexylresorcinol and some flavones or flavonols on potato polyphenol oxidase were then studied using this partially puried enzyme. The inhibitory mecharisms were determined and the inhibition constants were caculated. Mushroom tyrosinase was used to compare with potato polyphenol oxidase. The results showed that tannic acid, gallic acid, L-Cysteine, 4-hexylresorcinol and quercetin had strong inhibitory effect on potato polyphenol oxidase. The IC50, inhibitor′s concentration leading to 50% activity lost, were estimated to be 46μmol/L,76μmol/L,100μmol/L,48μmol/L and 69μmol/L respectively. Among these inhibitors, the inhibition kinetics analyzed by Lineweaver-Burk plots showed that tannic acid, 4-hexylresorcinol, quercetin and gallic acid were competitive inhibitors for the oxidation of L-DOPA, and their inhibition constants were 30.2μmol/L, 35.1μmol/L, 45.8μmol/L and 86.8μmol/L respectively. The reaction of L-Cysteine with remaining enzyme activity was irreversible, and L-Cysteine could also react with o-quinones, the product of enzyme reaction, to form colorless and stable compounds.Some other flavones or flavonols, such as naringenin, rutin trihydrate, morin had less inhibitory effect on potato polyphenol oxidase compared with quercetin. The IC₅₀ values of naringenin and rutin...