芒果多酚氧化酶的特性及抑制研究

以邻苯二酚为底物,采用分光光度法在420nm处测定芒果多酚氧化酶(PPO)的活性,研究了温度、pH值、底物浓度对其活性的影响,并建立了酶促褐变反应动力学方程,探讨了L-半胱氨酸、抗坏血酸、亚硫酸氢钠、柠檬酸和醋酸五种抑制剂对芒果酶促褐变的抑制效果。结果表明,芒果多酚氧化酶的最适温度为50℃,最适pH值为6.86;酶促褐变反应动力学符合米氏方程所描述的单底物酶促反应动力学,以邻苯二酚为底物的最大反应速度Vmax=192(U/min·g),Km=0.0173mol/L,相应的动力学方程为v=192S]/(0.0173+S]);五种物质对该酶均表现出不同的抑制作用,抑制效果为:抗坏血酸>L-半胱氨酸>亚硫酸氢钠>柠檬酸>醋酸。

Study on Characters and Inhibition of PPO in Mango Fruit

The activity of mango polyphenol oxidase (PPO) was determined by spectrophotometer at 420nm using catechol as substrate. The effects of the temperature, pH, substrate concentration and inhibitors on PPO were studied and the reaction kinetic equation was established. The results showed that the optimum temperature and pH were 50℃ and pH6.86, respectively. The reaction kinetic of enzymatic browning in this experiment built accorded with Michaelis Equation model. The Km, Vmax and kinetic Equation were 0.0173mol/L, 192U/g·min and v=192S]/(0.0173+S]) using catechol as substrate, respectively. The five inhibitors had different effects on inhibiting enzymatic browning and the inhibiting effect as follow: ascorbic acid>L-cysteine >sodium hydrogen sulfite>citric acid>acetic acid.