Strawberry Polyphenoloxidase: Its Role in Anthocyanin Degradation

Abstract

ABSTRACT Two purified fractions of strawberry polyphenoloxidase (PPO) were used in model systems containing D‐catechin alone or in combination with either pelargonin or cyanin. Km values using D‐catechin were 0.5 mM and 0.41 mM and Vmax 82,700 and 18,800 nmoles O 2 /min/ mg protein, respectively, for each isozyme. Reaction of PPO with D‐catechin led to the formation of yellow‐brown pigments with maximum absorbance at 390 nm. Little PPO activity could be detected using cyanin as a substrate and no activity with pelargonin. PPO and D‐catechin together caused the loss of 50 to 60% of the anthocyanin pigments after 24 hr at room temperature with the formation of a precipitate.