What is Oxidation?
Oxidation is a chemical process in which a substance loses electrons, often through reaction with oxygen. In food, it affects fats, vitamins, and the appearance of cut fruit and vegetables.
Lipid Oxidation
This is the reaction between fats and oxygen, breaking down fatty acids and forming potentially harmful compounds. Free radicals attack fat molecules, triggering a chain reaction that can lead to rancidity, off-flavours, and the loss of essential fatty acids like omega-3s.
Vitamin Oxidation
Vitamins A, C, and E are particularly susceptible to oxidation. Vitamin C is sensitive to heat, light and oxygen and loses its antioxidant properties when oxidized; Vitamin A can degrade into less active forms; and Vitamin E, itself an antioxidant, can become depleted by oxidative processes.
Enzymatic Browning
When fruits and vegetables are cut or damaged, the enzyme polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds, producing brown pigments. This affects appearance and can make the food taste more bitter, with some nutrient loss.
Controlling Oxidation
- Storage conditions: keep fats and oils in cool, dark places, and minimize exposure to air by sealing containers tightly.
- Antioxidants: foods rich in natural antioxidants (berries, citrus, leafy greens, nuts and seeds) help prevent oxidation; manufacturers may also add antioxidants like vitamin E or vitamin C to processed foods.
- Processing techniques: vacuum packaging reduces oxygen exposure, and preservatives can inhibit oxidation.
- Handling practices: avoid overheating oils and fats, and use fresh produce and meat promptly.
Why It Matters
Oxidation reduces the nutritional value of fats and vitamins, causes rancidity and undesirable colour changes, and consuming oxidized fats and vitamins is linked to oxidative stress and health issues such as cardiovascular disease.
