求下面这段有关多酚氧化酶的翻译？十分感谢！！

Polyphenol oxidase is caused enzymatic browning of fruits and vegetables major enzymes, cause browning of fruit juice most important factor. PPO sources are different, their physical and chemical properties are fairly different. thus on the same physical or chemical treatment sensitivity, in practice, according to the food of different types of raw materials, source and processing characteristics, reasonable choice PPO activity in the method for improving the quality of products is important. This study analyzes four apple varieties PPO certain nature, that is, pH, temperature, inhibitors of the activity, with a view to processing apples inhibit browning improve product quality frame of reference. Preparation of liquid nitrogen with good fruit extract powder PPO enzyme used Spectrophotometry PPO activity by the experimental study of pH, temperature, substrate, the substrate concentration and the activity of inhibitors of the impact. The results showed : catechol as substrate, PPO Th