Polyphenoloxidase is an enzyme present in many types of foods like fruits, vegetables, mushrooms, etc. It plays a role in protecting the plants from bacteria and viruses and enables them to withstand adverse weather conditions.
This enzyme acts as a catalyst in a reaction that takes place when fruits are cut. The reaction leads to the formation of dark polymers known as melanins which discolor the foods and lead to their browning.
Browning can be reduced to a large extent by rendering the enzyme inactive. This is down by heating it. Polyphenoloxidase is destroyed when food is heated to temperatures above 100 degree Celsius. Blanching can be done either by scalding the food by exposing it to hot water or steam, or it can be achieved by microwaving the food.