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

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.