Cooks often put cut apples or potatoes in a water bath until they are ready to be cooked. The water reduces contact with oxygen and prevents enzymatic browning. Cooking fruits or vegetables inactivates (destroys) the PPO enzyme, and enzymatic browning will no longer occur. Refrigeration can slow enzymatic browning.

The most important factors that determine the rate of enzymatic browning of vegetables and fruits are the concentration of both active PPO and phenolic compounds present, the pH, the temperature and the oxygen availability of the tissue.

According to this article, the actual mechanism that causes browning in apples and potatoes involves an enzyme called polyphenol oxidase, also known as tyrosinase. The enzyme then has access to oxygen in the air and it does its thing, turning the fruit brown.

Non-enzymatic browning involves a set of chemical reactions that take place during the preparation or storage of foods. It is responsible for the formation of brown compounds, which are volatile flavor molecules that affect the sensory quality of foods.

Enzymatic browning is initiated in the flesh and seeds from fruits harvested at the horticultural stage of maturity (weeks eight to ten after fruit set) upon exposure to air when peeled, sliced or diced within five minutes.

The Maillard Reaction is known to create a carcinogen called Acrylamide. It’s so serious the food standard agency is working to reduce the amount of Acrylamide in our own human food. It is a risk to humans but has been proven to be a more significant risk to our pets.

The Maillard reaction, or non-enzymatic browning reaction, between reducing sugars and proteins (amino acids), is known to cause serious deterioration of food quality during processing and storage.

Maillard reaction is strongly influenced by the pH which increases with increasing pH. At low pH, the amino group was protonation, so only a few amino groups were available for Maillard reaction (El-Ghorab et al., 2010).