Many food raw materials contain natural antioxidants which exert control of oxidative processes in the living cells. Among antioxidative agents are found enzymes such as superoxide dismutase, glutathione peroxidase and glucose oxidase-catalase. Among naturally occurring non-enzymic antioxidants are carotenoids, especially astaxanthin (e.g. in fish), tocopherols in oils and other phenolic compounds in plant material. Enzymic antioxidants are mostly inactivated in food processing but the non-enzymic ones can be active also in heat-treated food and might also be active after consumption of the food, as is claimed with ϐ-carotene, and vitamins A and E. Vitamin C is a generally reducing substance which acts synergistically with other antioxidants. Processing of food can result in the formation of antioxidative compounds, e.g. by protein hydrolysis, Maillard reaction and fermentation by lactic acid bacteria. Curing of meat yields nitrosylhaem pigments which can act as radical scavengers and protect both the meat pigment and the lipids from oxidation. Two or more antioxidants together can act synergistically, i.e. affect lipid oxidation to a higher extent than the sum of the contributions from each single antioxidant.

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