本文以富士苹果中含量较多的绿原酸、儿茶素、表儿茶素和根皮苷为苹果多酚氧化酶（PPO）作用底物，以磷酸盐缓冲液为苹果汁酶促褐变模拟体系，通过连续测定酶促褐变模拟体系吸光度A420值的变化趋势，研究不同苹果多酚底物对PPO酶促催化特性的影响，并确定多酚氧化酶对该4种底物较适作用条件。结果表明，苹果多酚底物对PPO反应特性影响较大；PPO酶促氧化绿原酸、儿茶素、表儿茶素和根皮苷4种多酚底物适宜的pH分别为5.0、4.0、4.5、4.5；适宜的温度分别为55、70、60、50 ℃；PPO作用适宜的底物浓度分别为5、0.5、2、10 mM；适当提高酶活可促进酶促褐变反应，且该4种底物对多酚氧化酶的亲和力大小为：儿茶素>表儿茶素>绿原酸>根皮苷。该研究为苹果汁褐变控制提供理论依据。

Influence of different apple polyphenols on the properties of polyphenol oxidase (PPO) was investigated and the suitable conditions of PPO enzymatic oxidation were obtained by employing chlorogenic acid, catechin, epicatechin and phlorizin as substrates and by determining the change of absorbance in the phosphate buffer model system. The results showed that the substrates had an important impact on the reactive characteristics of PPO. The optimum pH of enzymatic oxidation of chlorogenic acid, catechin, epicatechin and phlorizin by PPO were 5.0, 4.0, 4.5 and 4.5, respectively. The best temperature of enzymatic oxidation of the above-mentioned substrates were 55, 70, 60 and 50 ℃, respectively. And the polyphenol substrate concentration for the four substrates were 5, 0.5, 2 and 10 mM, respectively. Furthermore, appropriate increase of enzyme activity could promote the enzymatic browning reaction. The affinity of the four substrates for PPO was in the order of catechin ? epicatechin﹥chlorogenic acid ? phlorizin. This study will supply a basis for browning control of apple juice.

国基自然科学基金项目（31101326）；咸阳市科技局自然科学项目（2010k12-16）