抄録
The polyphenol oxidase (PPO) activity in the leaves, stalk or flesh, and core or peel of seven vegetables was determined, and the temperature, time and pH value required for the thermal inactivation of the enzyme were investigated. The PPO activity was highest at the bottom of the stalk in spinach, celery and komatsuna and in the core of cabbage, while the PPO activity in radish, carrot, and onion was highest in the peel. The enzyme activity was rapidly decreased by incubating for 10min at a temperature above 50℃ for celery and 60℃ for spinach, cabbage and komatsuna, whereas the carrot PPO activity was gradually decreased above 60℃ and reduced to 19% by heating at 70℃ for 10min. The enzyme obtained from carrot was the most heat resistant, requiring 59.3min at 65℃ for 90% reduction of the activity. The z value of PPO prepared from five vegetables ranged from 6.1℃ to 11.5℃. A change in pH from 5.5 to 4.0 resulted in a substantial reduction in the D value of radish PPO.
