EFFECTS OF GREEN TEA EXTRACT ON “GOLDEN DELICIOUS” APPLE POLYPHENOLOXIDASE AND ITS BROWNING

Abstract

ABSTRACT The inhibitory effect of green tea extract on apple polyphenol oxidase (PPO) and on apple browning was investigated. PPO has been isolated from apples (cv. Golden Delicious), and extraction with polyvinylpolypyrrolidone and Triton X100 yielded a 6.45-fold increase in the specific enzyme activity. The optimum pH and temperature of the enzyme was found as 5.5 and 25C, respectively. The kinetics of enzyme-catalyzed reactions followed the Michaelis-Menten model, and the PPO exhibited a Km value of 4.76 mM. Apple PPO activity was inhibited by green tea extract, and the inhibitory effect toward apple PPO increased with increasing extract concentration. Addition of 30 mg/mL green tea extract resulted in approximately 42% inhibition on apple PPO activity. To support the inhibition behavior of PPO, apple browning was also investigated by immersing apple slices into green tea extract, and it was revealed that the browning of apple slices was effectively retarded by the green tea extract. PRACTICAL APPLICATIONS The quality of fruits, especially apples, depends on controlling the enzymatic browning that affects its organoleptic and nutritional qualities. Addition of chemicals, pH adjustment, refrigeration, thermal treatments and exclusion of oxygen are among the most effective methods for the inhibition of polyphenol oxidases (PPO). Consumer demand for minimally processed and fresh-like food products has undergone a continuous rise in recent years. Several authors have stated the necessity to evaluate the inhibitory effect of natural and nontoxic compounds on PPO activity and its potential applicability to the food industry. Experiments showed that green tea has an inhibitory effect on the activity of apple PPO and its browning. Our results suggest that green tea extract could potentially be used as a natural inhibitor of PPO, and its utilization is possible due to its wide occurrence, low cost and nontoxicity, but further feasibility studies are needed to increase its effect as an anti-browning agent in its application in the food industry.