Enzymatic browning is a specific type of oxidation that occurs in some fruits and vegetables, particularly apples, bananas, peaches, pears, and potatoes, which contain phenolase enzymes. When these fruits and vegetables are cut or sliced and exposed to air, phenolases catalyze the oxidation of phenolic compounds to ortho-quinone compounds. These compounds then polymerize, forming brown pigments. This browning not only affects the aesthetic quality of the produce but can also alter its taste and nutritional value.
In foods high in fats and oils, oxidation occurs in the form of autoxidation. This process is the result of the susceptibility of fatty acids, the building blocks of fats and oils, to oxidation and the subsequent formation of reactive compounds known as free radicals. These free radicals promote a series of chemical reactions leading to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are prone to oxidation, unsaturated fatty acids are significantly more susceptible, especially at room temperature and elevated temperatures.
To combat these undesirable effects, antioxidants are commonly used. The Food and Drug Administration (FDA) defines antioxidants as substances used to preserve food by retarding deterioration, rancidity, or discoloration due to oxidation. Antioxidants can function in multiple ways. For example, ascorbic acid (vitamin C) may act as a free-radical chain terminator, oxygen scavenger, or metal chelator. However, under certain conditions, ascorbic acid can also act as a promoter of oxidation, highlighting the complex nature of oxidation reactions in food.
Understanding the mechanisms of oxidation and the role of antioxidants is crucial in food preservation. By controlling exposure to air, light, and heat, and by using antioxidants, the shelf life and quality of food products can be significantly improved, ensuring better taste, appearance, and nutritional value for consumers.
Oxidation in Foods: Causes, Effects, and Prevention
