为探究苹果多酚氧化酶(PPO)酶促诱发因素对苹果多酚参与的非酶褐变的影响，以绿原酸和根皮苷为底物，以磷酸缓冲液为苹果汁模拟体系，通过控制PPO酶促诱发条件，进行酶促诱发反应，然后钝化酶，模拟体系于60 ℃进行非酶聚合反应，每隔24 h用色差计测定L*值、a*值、b*值和ΔE*值。结果表明，酶促诱发因素对绿原酸和根皮苷参与的非酶褐变的影响存在较大差异。pH在3.5~6.0，含有绿原酸和根皮苷的模拟体系，其褐变程度随酶促诱发pH升高而增大；酶促诱发温度20~60 ℃，诱发体系温度对绿原酸参与的非酶褐变影响不显著，而根皮苷在40 ℃时褐变程度较大；酶促诱发时间分别为40 min和30 min时绿原酸和根皮苷参与的非酶褐变程度较大；酶活14.25~171 U，酶活的增大加速两种多酚参与的非酶褐变。结果同时表明，根皮苷非酶褐变与果汁后浑浊有关，且较高的pH、温度、PPO酶活以及较长的酶促诱发时间加速果汁后浑浊形成。

In order to study the effects of apple polyphenol oxidase (PPO) enzymatic inducing factors on the non-enzymatic browning of apple polyphenols, chlorogenic acid and phlorizin were used as reaction substrates, and phosphate buffer was used as the model apple juice system to carry out enzymatic induction under controlled enzymatic induction conditions. Subsequently, the enzyme was deactivated, and the non-enzymatic polymerization in the model apple juice system was carried out at 60 ℃; L*, a*, b*, and △E* values were measured using a colorimeter every 24 h. The results showed that significant differences were found in the impacts of enzymatic inducing factors on the non-enzymatic browning involving chlorogenic acid and phlorizin. In the 3.5~6.0 pH range, the degree of browning in the model juice system containing chlorogenic acid and phlorizin increased with increasing pH values. When the temperature of enzymatic induction was between 20 and 60 ℃, the temperature of the inducing system had no significant effect on the non-enzymatic browning involving chlorogenic acid, while the degree of non-enzymatic browning in the model juice using phlorizin was higher at 40 ℃. A higher degree of non-enzymatic browning was achieved for the model juice using chlorogenic acid and phlorizin when the durations of enzymatic induction were 40 and 30 min, respectively. When the PPO activity was in the range of 14.25~171 U, the increasing enzymatic activity could accelerate the non-enzymatic browning involving chlorogenic acid and phlorizin. Meanwhile, the results indicated that non-enzymatic browning involving phlorizin was related to the haze occurring in apple juice, and the development of the haze in apple juice could be accelerated by increasing the pH, temperature, PPO activities, and duration of enzymatic induction.

国家自然科学基金项目（31101326）；咸阳市科技局自然科学项目（2010k12-16）