Why Do Apples Turn Brown?

Many have asked the question “why do apples turn brown?”. Apples turn brown when the phenolic compounds typically found in the fruits react with oxygen. This oxidation process is driven by the Polyphenol oxidase (PPO) enzyme. Upon wounding, bruising or other cell rupture situations, PPO is able to react with the phenolics and the browning reaction begins.

We have been able to learn from apple genomic investigation that apples actually have at least eight PPO genes and that these are in three main PPO gene families.  Some apples turn brown more slowly then others, which can be due to a number of factors. The apple variety may be high in acid, which impedes the reaction; it may be low in phenolic substrate; it may have stronger cell walls, which reduce the mixing of PPO; or it may be that it has naturally low levels of PPO.  In general, to make a non-browning apple, the developer must silence all of the PPO genes active in the fruit.

Learn more on The Non-Browning Apple.