What is enzymic browning primarily caused by?

Enzymic browning is primarily caused by the reaction between oxygen and enzymes present in plant cells. When fruits and vegetables are cut or bruised, their cells are damaged, allowing enzymes, specifically polyphenol oxidase, to interact with phenolic compounds in the presence of oxygen. This interaction leads to the formation of brown pigments, typically melanins, as a byproduct of the enzymatic reaction.

This process is particularly notable in fruits such as apples, bananas, and avocados, which are susceptible to browning once their protective skin is removed. Preventing enzymic browning can be achieved through methods such as applying acidic substances (like lemon juice) to inhibit enzyme activity or reducing exposure to oxygen by sealing the food in airtight containers.

The other options, while they describe processes that can cause changes in food, do not accurately represent the primary cause of enzymic browning. The reaction between sugar and acid is related to caramelization, while light and moisture, or heat and moisture, can contribute to different types of food spoilage or quality changes, but they do not account for the enzymatic reaction responsible for browning.