酶促诱发儿茶素对模拟苹果汁非酶褐变特性的影响

以苹果中含量较多的儿茶素为研究对象，以磷酸缓冲液为苹果汁褐变模拟体系，在多酚氧化酶（polyphenol oxidase，PPO）酶促诱发儿茶素后，钝化PPO，通过色差仪连续测定模拟体系亮度（L*）值、红度（a*）值、黄度（b*）值及总色差（ΔE*）值的变化趋势，研究酶促诱发条件对模拟果汁体系非酶褐变特性的影响。结果表明：酶促诱发时间及诱发体系温度对儿茶素参与的非酶褐变无显著性影响（P＞0.05），而酶促诱发体系pH值以及儿茶素浓度对模拟体系褐变程度影响显著（P＜0.05），pH 4.0时，模拟果汁体系褐变程度较大，褐变程度随儿茶素浓度的增大而增强；本实验同时发现，PPO诱发儿茶素发生非酶聚合，并与聚合产物相互作用而沉淀，导致果汁产生后浑浊。

Effect of Enzymatic Induction of Catechin by Polyphenol Oxidase on Non-Enzymatic Browning Properties in Model Apple Juice

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.