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An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction that can produce free radicals, leading to chain reactions that may damage cells. Antioxidants such as thiols or ascorbic acid (vitamin C) terminate these chain reactions. The term "antioxidant" is mainly used for two different groups of substances: industrial chemicals which are added to products to prevent oxidation, and natural chemicals found in foods and body tissue which are said to have beneficial health effects.

To balance the oxidative state, plants and animals maintain complex systems of overlapping antioxidants, such as glutathione and enzymes (e.g., catalase and superoxide dismutase) produced internally or the dietary antioxidants, vitamin A, vitamin C, and vitamin E.

Antioxidant dietary supplements do not improve health nor are they effective in preventing diseases. Randomized clinical trials including supplements of beta-carotene, vitamin A, and vitamin E singly or in different combinations found no effect on mortality rate and cancer risk, or may even increase cancer risk. Supplementation with selenium or vitamin E does not reduce the risk of cardiovascular disease. Oxidative stress can be considered as either a cause or consequence of some diseases, an area of research stimulating drug development for antioxidant compounds for use as potential therapies.

 

Foods Reducing acid present
Cocoa bean and chocolate, spinach, turnip and rhubarb. Oxalic acid
Whole grains, maize, legumes. Phytic acid
Tea, beans, cabbage. Tannins
Antioxidant metabolite Solubility Concentration in human serum (μM) Concentration in liver tissue (μmol/kg)
Ascorbic acid (vitamin C) Water 50 â€“ 60 260 (human)
Glutathione Water 4 6,400 (human)
Lipoic acid Water 0.1 â€“ 0.7 4 â€“ 5 (rat)
Uric acid Water 200 â€“ 400 1,600 (human)
Carotenes Lipid β-carotene: 0.5 â€“ 1

retinol (vitamin A): 1 â€“ 3

5 (human, total carotenoids)
(vitamin E) Lipid 10 â€“ 40 50 (human)
Ubiquinol (coenzyme Q) Lipid 5 200 (human)
Fuel additive Components Applications
AO-22 N,N'-di-2-butyl-1,4-phenylenediamine Turbine oils, transformer oils, hydraulic fluids, waxes, and greases
AO-24 N,N'-di-2-butyl-1,4-phenylenediamine Low-temperature oils
AO-29 2,6-di-tert-butyl-4-methylphenol Turbine oils, transformer oils, hydraulic fluids, waxes, greases, and gasolines
AO-30 2,4-dimethyl-6-tert-butylphenol Jet fuels and gasolines, including aviation gasolines
AO-31 2,4-dimethyl-6-tert-butylphenol Jet fuels and gasolines, including aviation gasolines
AO-32 2,4-dimethyl-6-tert-butylphenol and 2,6-di-tert-butyl-4-methylphenol Jet fuels and gasolines, including aviation gasolines
AO-37 2,6-di-tert-butylphenol Jet fuels and gasolines, widely approved for aviation fuels
Antioxidant vitamins Foods containing high levels of antioxidant vitamins
Vitamin C (ascorbic acid) Fresh or frozen fruits and vegetables
Vitamin E (tocopherols, tocotrienols) Vegetable oils, nuts, and seeds
Carotenoids (carotenes as provitamin A) Fruit, vegetables and eggs


2 Fe3+ + Ascorbate → 2 Fe2+ + Dehydroascorbate

2 Fe2+ + 2 H2O2 → 2 Fe3+ + 2 OH· + 2 OH−

2 Fe2+ + 2 H2O2 → 2 Fe3+ + 2 OH· + 2 OH−

  • Nick Lane Oxygen: The Molecule That Made the World (Oxford University Press, 2003)
  • Barry Halliwell and John M.C. Gutteridge Free Radicals in Biology and Medicine (Oxford University Press, 2007)
  • Jan Pokorny, Nelly Yanishlieva and Michael H. Gordon Antioxidants in Food: Practical Applications (CRC Press Inc, 2001)

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