生菜属褐变敏感型蔬菜，酶促褐变严重影响其营养品质和商品价值，抑制酶促褐变是当前生菜贮藏加工中亟待解决的关键科学问题。本项目组前期研究发现，高强度光照(2500Lux)降低鲜切生菜PPO活性，减缓酶促褐变，但其调控机制目前尚不清楚。本项目拟在此基础上应用分光光度计、透射电镜、聚丙酰胺凝胶电泳、氨基酸分析仪、圆二色光谱技术研究2500Lux光照对外源性和内源性PPO酶活性、分子形态、分子量、同工酶、一级结构、二级结构变化的影响，从形态、结构和构象上探索高强度光照抑制PPO活性机制。同时，采用高效液相色谱技术研究高强度光照对总酚类物质含量、合成前体物质苯丙氨酸含量、合成关键酶L-苯丙氨酸解氨酶(PAL)活性以及氧化产物苯醌含量的影响，阐明高强度光照调控总酚物质代谢规律。本研究对揭示高强度光照抑制PPO活性机制和酶促褐变基础物质代谢规律具有重要理论意义，为探索抑制果蔬酶促褐变研究提供崭新思路。

Lettuce is susceptible to enzymatic browning, resulting in quality decay and economic loss. In the previous study, we found that high intensity (2500Lux) light （HIL）exposure is efficient to inhibit PPO activity and subsequently alleviate enzymatic browning of fresh-cut lettuce. However, the mechanism is unclear until now.To clarify the mechanism of HIL inhibiting PPO activity and enzymatic browning, this research investigates the effect of HIL exposure on exogenous and endogenous PPO characteristics associated with enzyme activity, molecular form, molecular weight, isoenzyme, primary structure,scondary structure by means of spectrophotometer, transmission electron microscopy (TEM),PAGE, amino acid analyzer and circular dichroism (CD). Meanwhile, total phenol content, aminohydrocinnamic acid, L-phenylalanin ammo-nialyase (PAL) activity and quinone content are also assayed to clarify the influence of HIL on phenolic metabolism using HPLC. The results obtained will be valuble to clarify the mechanism of HIL exposure inhibiting PPO activity and substance metabolism related to enzymatic browning, and provide an innovative idea for fresh fruits and vegetables browning inhibition.