Fruit/Vegetables - Enzymic Browning, Oxidation

Basic Understanding

Enzymic browning is a natural process that leads to a change in colour of fruits and vegetables after being cut or bruised.
This reaction is caused by the enzyme polyphenol oxidase (PPO), which is released when the cells of the fruit or vegetable are damaged.
The enzyme interacts with oxygen in the air and oxidises phenolic compounds present in the cells to produce melanin, a brown pigment.

Lemon juice or vinegar, which is high in vitamin C and acid, can be applied to the cut surface to prevent enzymic browning. The acid lowers the pH which inhibits the enzyme’s activity.
Cooking can be used to control enzymic browning. Heat denatures the enzymes, stopping the reaction.
Chilling or freezing the fruits or vegetables can slow down the reaction, but it does not stop it completely.
Reducing exposure to air, for example by using vacuum packaging or covering with cling film, can also help to slow down the reaction.

Oxidation is a chemical reaction that happens when fruits and vegetables are cut open and exposed to oxygen.
This reaction can lead to not only colour changes but also loss of nutrients, specifically vitamin C (ascorbic acid).
Like enzymic browning, the effects of oxidation can be minimised by reducing exposure to air, applying acid, or by cooking the fruits or vegetables.

While enzymic browning does not affect the nutritional value, it can make the fruits or vegetables look less appealing, affecting their aesthetic value and potentially increasing food waste.
Oxidation, on the other hand, can result in nutrient loss, thereby lessening the nutritional value of the fruits or vegetables.
Understanding and managing these reactions is therefore important in food preparation and ensuring the nutritional quality of meals.