Apple waste management: a study on polyphenol oxidase activity

Abstract

The enzymatic browning of apples by polyphenol oxidase is a major drawback in the food industry. The change in the color, taste, and texture discourage the client from buying these fruits in the market. The description of this enzyme’s characteristics can be helpful in preventing the adverse consequences of the reaction. A study was carried out using polyphenol oxidase extracted from “Red delicious” apples cultivated in Laklouk, a small mountainous village located 69 km northeast of Beirut, Lebanon. The enzyme extraction was performed using phosphate buffer (0.1 M, pH 6.5), ascorbic acid, 3% polyvinylpolypyrrolidone, and 0.5% TritonX-100. The enzymatic reaction catalyzed by polyphenol oxidase was held using pyrocatechol (20 mM) as substrate. The optimum temperature and the optimum pH at which the enzyme shows maximal activity were determined. The stability of the enzyme after incubation at different temperatures was studied, and the major kinetic and thermodynamic parameters were calculated. The enzyme exhibits optimal activity at pH 5.5 and at 303 K. Higher or lower temperatures majorly reduce the enzyme activity. Apple polyphenol oxidase heat inactivation showed a first-order decay approach. The means of thermodynamic parameters suggest that polyphenol oxidase catalyzed reaction is endergonic with insignificant dispersion in the reaction medium. The results also provided information on the stability and structural resistance of the enzyme. This study determines for the first time some characteristics of polyphenol oxidase extracted from Lebanese apples. The knowledge of the enzyme activity can generate helpful instructions. This data taken into consideration while harvesting, handling, and processing apples, will help in reducing undesirable wastage of fruits and permitting economical savings.