白萝卜作为我国第二大蔬菜。其贮运和加工过程中的褐变多以酶促褐变为主，全面系统地了解白萝卜多酚氧化酶（PPO）的酶学特性，并研究其抑制手段，对提升白萝卜及其制品的品质和商品价值有着重要的意义。本文以新鲜白萝卜为原材料，采用丙酮洗涤、0.2 mol/L磷酸盐缓冲溶液匀浆法从中提取PPO，考察了pH、温度对酶活的影响，分析了其温度稳定性、底物浓度对PPO活性的影响，探讨了过程的反应动力学，并对多种酶抑制剂对PPO活性的影响进行了比较，为控制加工过程中白萝卜的酶促褐变提供了理论依据。试验结果表明：以邻苯二酚为底物，该酶的最适pH 值为6.0，最适反应温度为40 ℃，Km和Vmax值分别为53.8 mmol/L和588 U/min。90 ℃热处理2.5 min或85 ℃热处理3.5 min可基本完全钝化其活性，Vc、异Vc和L-cys对PPO酶活的抑制较为明显。

As the second major vegetables in China, the mainly browning of white radish during its storage and processing was enzymatic browning. A comprehensive and systematic understanding of polyphenol oxidase (PPO) in white radish and its suppression means is of great significance to promote quality and commercial value of white radish and its products. In this study, the fresh white radish was taken as the material, the PPO was extracted and characterized. The results showed that,with catechol as substrate, the optimum pH and reaction temperature of the enzyme were 6.0 and 40 ℃, respectively. Km and Vmax were 53.8 mmol/L and 588 U/min, respectively. The enzyme activity was completely inactivated by heating at 90 ℃ for 2.5 min or 85 ℃ for 3.5 min, and ascorbic acid, isoascorbic acid as well as L-cys had obvious inhibition effects on the PPO enzyme activity.

浙江省重点科技创新团队项目(2010R50032)