One question that often accompanies yours is, "Why do some apples seem to brown faster than others?"
Well, nearly all plant tissues contain PPO, however, the level of PPO activity and concentration of substrate--here, the phenolic compounds--can vary between varieties of fruits (say, Granny Smith versus Red Delicious). In addition, a tissue's PPO level can vary depending on growing conditions and fruit maturity. One approach the food industry employs to prevent enzymatic browning is to select fruit varieties that are less susceptible to discoloration—either due to lower PPO activity or lower substrate concentration. This approach, however, may not be practical for the home "culinary scientist."