Why Apple Turns Brown After Cutting?

When apples are sliced, they start to brown after a while, which is a common occurrence. Many people think this happens because of the iron content in apples, but that’s not true. This process is actually caused by an enzyme called polyphenol oxidase that reacts with oxygen.

Polyphenol oxidase, which is naturally present in fruits like apples, becomes active when the cells are damaged. When an apple is cut or bruised, the cell walls break, and the enzyme comes into contact with oxygen. This reaction leads to the oxidation of phenolic compounds within the apple. As a result, substances called o-quinones are formed. These o-quinones then interact with nearby amino acids or proteins, leading to the production of melanin, a brown pigment, which causes the color change in the fruit.

This reaction doesn’t only occur in apples but can also be seen in pears, bananas, and eggplants. Polyphenol oxidase is also responsible for the brownish tones in tea, coffee, and cocoa. Thus, this process is a natural defense mechanism in plants.

There are several ways to slow down or stop the effects of polyphenol oxidase:

• Blanching the apples: The heat from hot water neutralizes the polyphenol oxidase enzyme and prevents browning. If iron were the cause of browning, water would not stop the process—in fact, it would speed it up.
• Using lemon or pineapple juice: The acids in these fruit juices slow down the reaction between oxygen and the polyphenol oxidase enzyme.

Genetic Engineering and the “Arctic” Apple

Scientists have made genetic modifications to completely eliminate browning by stopping polyphenol oxidase enzyme production.

A genetically modified variety of apple, called the Arctic apple, doesn’t brown at all because the production of polyphenol oxidase is blocked. This genetic modification does not affect the taste or nutritional value of the apple.

In summary, the browning of apples is not caused by iron oxidation but is an enzymatic process involving the interaction of polyphenol oxidase with phenolic compounds. Using the methods mentioned above, it’s possible to slow down this process.

Thanks to genetic engineering, apple varieties that don’t brown at all have been developed. This innovation helps extend the shelf life of the products and offers consumers more visually appealing apples. While apples do contain some iron, the amount is quite small—only about 0.12 mg of iron in 100 grams of apple flesh, and it is not absorbed efficiently by the body due to its plant-based origin.