Characterization of Polyphenoloxidase from Ravat 51 and Niagara Grapes

Abstract

ABSTRACT Polyphenoloxidase (PPO) was isolated from two varieties of grapes grown in the northeastern United States and its characteristics were studied. The temperature and pH optima for both enzymes were 25°C and 5.5, respectively. The thermal inactivation of PPO followed first‐order kinetics; with the Niagara enzyme being more heat stable than Ravat PPO. The substrate specificity of the grape PPO clearly showed high affinity toward the o‐diphenolic compounds, with a high affinity toward caffeic acid. Inhibition studies indicated that L‐cysteine and sodium diethyldithiocarbamate were the most potent.