Why Apples Turn Brown: Unraveling the Mystery

Browning is a common issue in many fruits, including apples, which can affect their appearance and taste. Scientists compared a browning-resistant apple variety called 'Rb-18' with a more susceptible variety, 'Fuji'. They found that 'Rb-18' had lower levels of polyphenol oxidase (PPO) enzyme activity and phenolic content compared to 'Fuji'. This enzyme, PPO, helps in turning fruits brown by breaking down certain substances. In 'Fuji', this enzyme was also more attracted to its main ingredient, catechol. By looking at the genetic instructions (transcriptome) and using a technique called RT-qPCR, researchers found that a gene called MdPPO7 plays a big role in making the apple flesh turn brown after it's cut. They tested this by injecting the MdPPO7 gene into apples and apple cells (calli), discovering that several substances like syringic acid, procyanidin, phloridzin, chlorogenic acid, gallic acid, catechin, and caffeic act as fuel for this browning process. Interestingly, a particular protein called MdWRKY3 was found to control the expression of MdPPO7. This protein binds to the instructions for the MdPPO7 gene and helps it work more, leading to browning. This study sheds light on how apples turn brown and might help in creating apple varieties that resist browning, keeping our apples looking and tasting fresher for longer.