Antioxidants fall under two basic categories, according to How Stuff Works. There are antioxidants derived from nutrition and antioxidants that are enzymes. Antioxidants that are nutrients include vitamin E, vitamin C, beta carotene and selenium.
Vitamin E is a catch-all name for eight isomers of tocopherol, claims How Stuff Works. The most powerful is alpha-tocopherol, which is fat-soluble and is useful in protecting cell membranes from attack by free radical oxygen molecules. Vitamin C is water-soluble and removes free radicals from the body. It also fights free radicals alongside vitamin E. Beta-carotene is a precursor of vitamin A and is also excellent at removing free radical molecules.
Selenium, as well as other trace elements such as zinc and manganese, are part of antioxidant enzymes, according to How Stuff Works. These enzymes include superoxide dismutase, glutathione peroxidase and catalase. These enzymes work together to first give an electron to a free radical, which produces hydrogen peroxide. The hydrogen peroxide molecule is then further broken down into water. The enzymes also repair DNA that has been damaged by free radicals while degrading and destroying oxidized proteins and fats.
Antioxidants that are not quite enzymes nor nutrients are CoQ10, which is necessary to produce energy in the cells and also protects against free radicals, says How Stuff Works. Uric acid and plant phytochemicals also seem to work like antioxidants.