Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form ("vitamer") of vitamin C. It was originally called L-hexuronic acid, but, when it was found to have vitamin C activity in animals ("vitamin C" being defined as a vitamin activity, not then a specific substance), the suggestion was made to rename L-hexuronic acid. The new name for L-hexuronic acid is derived from a- (meaning "no") and scorbutus (scurvy), the disease caused by a deficiency of vitamin C. Because it is derived from glucose, many animals are able to produce it, but humans require it as part of their nutrition. Other vertebrates lacking the ability to produce ascorbic acid include other primates, guinea pigs, teleost fishes, bats, and some birds, all of which requiring it as a dietary micronutrient (that is, in vitamin form). There exists a D-ascorbic acid, which does not occur in nature. It may be synthesized artificially. It has identical antioxidant properties to L-ascorbic acid yet has far less vitamin C activity (although not quite zero). This fact is taken as evidence that the antioxidant properties of ascorbic acid are only a small part of its effective vitamin activity. To be specific, L-ascorbate is known to participate in many specific enzyme reactions that require the correct epimer (L-ascorbate and not D-ascorbate).
Ascorbic acid is mainly produced through the Reichstein-Grüssner process which is invented in 1933 until recent years. Nowadays, D-sorbital is typically converted to ascorbic acid through 2-keto-L-gulonic acid (SKGA) as the key intermediate, via bio-oxidation process involving Gluconobacter oxydans and several chemical steps.
Ascorbic acid and its sodium, potassium, and calcium salts are commonly used as antioxidant food additives. These compounds are water-soluble and, thus, cannot protect fats from oxidation: For this purpose, the fat-soluble esters of ascorbic acid with long-chain fatty acids (ascorbyl palmitate or ascorbyl stearate) can be used as food antioxidants.
Ascorbic acid is commonly added to poultry and livestock feed to enhance its immunity system. It is also commonly added into their diets to combat heat stress, and as a supplement in post-weaning diets for pigs.
Ascorbic acid promotes germination of seeds, growth of plants, and growth of roots on cuttings. When ascorbic acid or sodium ascorbate solutions is sprayed on plants such as lettuce, celery, spinach, petunias, and roses enabled those plants to better withstand damage from ozone and smog exposure.
Ascorbic acid (Vitamin C) is used in medicine to maintain proper immune function. It is also used in medicine to treat disease called scurvy. It is even used in skin creams which are used to protect or cure wrinkled skin due to sun exposure.
Ascorbic acid is used as a reductant in photographic developer solutions. In fluorescence based techniques, ascorbic acid can be used as an antioxidant to increase fluorescent signal and chemically retard dye photobleaching. It is also commonly used to remove dissolved metal stains, such as iron, from fiberglass swimming pool surfaces. In plastic manufacturing, ascorbic acid can be used to assemble molecular chains more quickly and with less waste than traditional synthesis methods. It is even used to negate the effects of iodine tablets in water purification.