Abstract:

The polyphenol oxidase (PPO) in phosphate buffer as a model apple juice browning system was inactivated byenzymatic induction of catechin, one of the major phenolic compounds identified in apples. The effect of different conditionsfor catechin induction by PPO on non-enzymatic browning properties of the model apple juice system was investigated bycontinuously measuring changes in color values (L*, a*, b*, and ΔE*). The results indicated that the enzymatic inductiontime and temperature had no significant impact on non-enzymatic browning properties of the model apple juice (P ＞ 0.05).However, pH and catechin concentration could significantly affect non-enzymatic browning properties of the model applejuice (P ＜ 0.05). A high degree of browning was developed in the model juice at pH 4.0, which was promoted by increasedcatechin concentration. Meanwhile, non-enzymatic polymers of catechin induced by PPO could interact with PPO, thusresulting in haze in the model juice.

Key words: catechin, polyphenols, polyphenol oxidase, non-enzymatic browning, enzymatic browning