为了解菊芋提取物氧化变色的机理,用分光光度法分别研究了以邻苯二酚为底物的酶促褐变反应动力学和pH值、温度、底物浓度、酶浓度对该反应的影响,以及不同底物对多酚氧化酶活性的影响,揭示了菊芋多酚氧化酶（PPO）的基本酶学性质.结果表明：菊芋PPO催化邻苯二酚氧化反应的最适pH值为4.8,最适温度为35℃;菊芋PPO的热稳定性差,85℃以上加热处理5min就可使其大部分失活;菊芋PPO酶促褐变反应动力学符合米氏方程所描述的规律,相应的动力学参数Km=0.013 mol/L,Vmax=7.5 mmol/s.菊芋PPO的活性随酶浓度的增加而增大,酶的添加量超过0.8mL后,增速逐步减小;菊芋多酚氧化酶对邻位多酚的氧化具有专一性.

In order to reveal the oxidation-induced browning mechanism of the extracts from Jerusalem artichoke,the basic enzymatic properties of polyphenol oxidase（PPO） in Jerusalem artichoke were investigated by using a spectrophometer,with catechol as the substrate.In the investigation,the kinetics of enzymatic browning was investigated,and the effects of pH value,temperature,substrate concentration and enzyme concentration on the browning,as well as the effects of different substrates on the emzyme activity,were analyzed.The results show that（1） the optimal pH value and temperature for the enzymatic oxidation are respectively 4.8 and 35℃;（2） the PPO in Jerusalem artichoke is of poor thermal stability,with most of it deactivating after being heated at 85℃ for 5min;（3） the enzymatic browning accords with the Michaelis equation,and the kinetic parameters Km and Vmax are respectively 0.013mol/L and 7.5mmol/s;（4） the activity of PPO first greatly and then slightly increases with the enzyme concentration,with 0.8mL as the critical PPO dosage;and（5） the PPO in Jerusalem artichoke only affects o-polyphenol.