The stability of water-soluble vitamins and issues in the fortification of foods

Vitamins are organic compounds, essential for normal metabolism. The human body cannot manufacture vitamins, with two exceptions: niacin, which can be synthesised from dietary tryptophan, and vitamin D, which can be synthesised when the skin is exposed to sunlight. However, dietary sources of niacin and vitamin D remain important as, depending on the amount of dietary tryptophan and level of exposure to sunlight, the amount synthesised may be insufficient to meet the needs of the body. Vitamins, or their precursors, are required in small amounts regularly from the diet. Vitamins are classified as being either fat-soluble vitamins-which are not discussed here-and those that are water soluble, comprising ascorbic acid (vitamin C) and the B group: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), B6 (pyridoxine, pyridoxal, pyridoxamine), biotin (B7), folate (B9) and cobalamin (B12). These vitamins are not generally stored in the body, except for folate and B12, found in the liver, and ascorbic acid occurring in many body tissues. When vitamin intakes would otherwise be too low-possible reasons include naturally low levels, processing losses, poor access to good nutrition, special needs-it may be appropriate to provide vitamins in supplements or through fortification. Some water-soluble vitamins are far more important as fortificants than others: fortification of cereal staples with thiamin, riboflavin, niacin and/or folate is performed either on a voluntary or mandatory basis in most countries around the world. Incorporation of ascorbic acid is also permitted in most countries and this is also commonly used as an antioxidant.