Oxidation, a series of chemical reactions yielding undesirable and products (off odors, colors, and flavors), may occur in many fruits and vegetables and foods high in fat and oil during exposure to air, light, heat, heavy metals, certain pigments or alkaline conditions.
Enzymatic browning may occur in some fruits and vegetables, particularly apples, banana, peaches, pear, and potatoes, which contain phenolase enzymes. Enzymatic browning is the rapid, enzyme-mediated conversion of plant phenolic compounds into dark polyphenolic polymers.
When these fruits and vegetables are cut or sliced and exposed to air, the phenolases catalyze oxidation of phenolics compounds to ortho-quinone compounds, which then polymerize, forming brown pigments.
Fruits and vegetables must be blanched and pretreated prior to pressing, in order to inactivate the enzyme.
Oxidation in lipids (autoxidation) and in fat and oil containing foods, on the other hand, occurs as a result of the susceptibility of fatty acids (building blocks of fats and oils) to oxidations and subsequent formation of reactive compounds referred to as “free radicals”.
The free radicals promote the development of a series of chemical reactions which lead to the production of off-flavors, colors, odors, and rancidity.
Some oxidations have more than one function. For example, ascorbic acids may function as a free-radical chain terminator, and oxygen scavenger, or a metal chelator. Under certain conditions, it may act as a promoter for oxidation.
Due to increasing concern over the potential toxicity and safety of some phenolic antioxidants, the replacement of synthetic antioxidants by ‘safe, natural’ antioxidants such as vitamins E and C flavonoids and other plant phenolic has received considerable attention.
Vitamin E compounds are reported to effectively inhibit lipid oxidation in foods and biological systems.
Vitamins as antioxidants in processed foods
