Why Do Apples Turn Brown When Exposed To Air?

By | April 9, 2018

The moment you cut an apple into pieces, it switches to a self destruction mode. And there begins a race against time with the apple turning into a flabby brown mess every second since then. Have you ever wondered what could be the possible reason behind it? Science has the answer. So, let’s unravel the mystery Of Why Do Apples Turn Brown When Exposed To Air?

why do apples turn brown

Ever Thought Why Do Apples Turn Brown When Exposed To Air | Discoverfoodtech.com

Why Do Apples Turn Brown? | Why Do Apples Brown

This unpleasant phenomenon is due to a series of biochemical reactions known as enzymatic browning. When an apple is cut, the injured plant tissue gets exposed to oxygen. The presence of oxygen in the cells causes an enzyme polyphenol oxidase(PPO) in the chloroplasts to oxidize phenolic compounds present naturally in the apple’s flesh to o-quinones. These new chemicals react with amino acids to produce brown colored melanins. Different varieties of apple contain different levels of PPO activity and thus they brown at different rates.

How To Preserve Cut Apples | How To Keep Apples Fresh After Cutting

Refrigeration can slow the reaction and hence prevent browning in apples. Lemon or pineapple juices, which contain natural antioxidants that inhibit the reaction, can also be used to coat apple slices. Also, enzymatic browning is reduced by the acids in these juices which slow down the reaction. The lower pH and acidic nature of the fruit juices causes less activation of PPO enzymes. Blanching of apples by boiling in water for a short time (4-5 mins) can eliminate PPO activity. Oxygen diffusion can be reduced by coating with honey, caramel or sugar and thus prevent browning.

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Why Do Apples Turn Brown

Nearly all plant tissues contain PPO, which is a mixture of monophenol oxidase and catechol oxidase. Browning is an unappetizing reaction; the familiar brown color of the beverages (tea, coffee and cocoa) consumed daily is developed by PPO enzymatic browning during processing of the product. Brown apples will someday be a thing of the past as the scientists are working to genetically engineer apples that do not produce the PPO enzyme.