黄冠梨果皮多酚氧化酶的酶学特性

目的]研究黄冠梨果皮中多酚氧化酶(PPO)的酶学特性,为黄冠梨的贮藏保鲜和加工提供理论基础。方法]采用分光光度法分别测定在不同反应pH值、不同反应温度、不同底物和抑制剂条件下的PPO活性。结果]该酶的最适温度为25℃,50℃以上PPO活力明显受抑制;最适pH值为6.0;以邻苯二酚为底物时,Km=0.031 7 mol/L;以绿原酸作为底物时,Km=0.018 9 mol/L;在选定的浓度范围内(0.2~1.0 mmol/L),所用抑制剂的抑制能力从强至弱排列为L-Cys>Vc>Na2S2O3>NaHSO3>EDTA-Na2。较高浓度的CaCl2、NaCl也可对黄冠梨果皮PPO产生抑制作用。Cu2+能提高黄冠梨果皮PPO活性。结论]绿原酸在黄冠梨果皮酶促褐变中的作用值得重视;采取调节pH值、热烫、添加安全抑制剂可以明显控制该PPO活性。

Enzymatic Characteristics of Polyphenol Oxidase in the Pericarp of Huangguan Pear

Objective] The research aimed to study the enzymatic characteristics of polyphenol oxidase(PPO) in the pericarp of Huangguan Pear and provide the theoretical foundation for the storage,preservation and processing of Huangguan Pear.Method] By using spectrophotometry,PPO activity was determined under different reaction pH value,different reaction temperature,different substrate and inhibitor.Result] The optimum temperature of this enzyme was 25 ℃ and PPO activity was obviously inhibited at over 55 ℃.The optimum pH value was 6.0.When pyrocatechol was taken as the substrate,Km=0.031 7 mol/L.When chlorogenic acid was taken as the substrate,Km=0.018 9 mol/L.In the range of selected concentrations(0.2-1.0 mmol/L),the inhibitory abilities of the used inhibitors were as follows: L-Cys>Vc>Na2S2O3>NaHSO3>EDTA-Na2.CaCl2 and NaCl at higher concentrations could inhibit PPO in the pericarp of Huangguan Pear.Cu2+ could increase PPO activity in the pericarp of Huangguan Pear.Conclusion] More attentions should be paid to the role of chlorogenic acid in the enzymatic browning of Huangguan Pear pericarp.PPO activity could be obviously controlled by adjusting pH value,blanching and adding safe inhibitors.