Chemistry of ascobic acid (vitamin C)
L-ascorbic acid (C6H8O6) is the trivial name of Vitamin C. The chemical name is 2-oxo-L-threo-hexono-1,4-lactone-2,3-enediol. L-ascorbic and dehydroascorbic acid are the major dietary forms of vitamin C [5]. Ascorbyl palmitate is used in commercial antioxidant preparations. All commercial forms of ascorbic acid except ascorbyl palmitate are soluble in water. L-ascorbic acid and its fatty acid esters are used as food additives, antioxidants, browning inhibitors, reducing agents, flavor stabilizers, dough modifiers and color stabilizers. Ascorbyl palmitate has been used for its greater lipid solubility in antioxidant preparations. In foods, pH influences the stability of ascorbic acid. It exhibits maximal stability between pH 4 and 6 [5]. Cooking losses of ascorbic acid depend on degree of heating, surface area exposed to water, oxygen, pH and presence of transition metals.
Catabolism of ascorbic acid (vitamin C)
Ascorbic acid present in foods is readily available and easily absorbed by active transport in the intestine [6]. Most of it (80–90%) will be absorbed when the in take is up to 100 mg/day, whereas at higher levels of intake (500 mg/day) the efficiency of absorption of ascorbic acid rapidly declines. Ascorbic acid is sensitive to air, light, heat and easily destroyed by prolonged storage and over processing of food.
Ascorbic acid being a water soluble compound is easily absorbed but it is not stored in the body. The average adult has a body pool of 1.2–2.0 g of ascorbic acid that may be maintained with 75 mg/d of ascorbic acid. About 140 mg/d of ascorbic acid will saturate the total body pool of vitamin C [7]. The average half life of ascorbic acid in adult human is about 10–20 days, with a turn over of 1 mg/kg body and a body pool of 22 mg/kg at plasma ascorbate concentration of 50 μmol/ L [8,9]. Hence ascorbic acid has to regularly supplemented through diet or tablets to maintain ascorbic acid pool in the body.
The major metabolites of ascorbic acid in human are dehydroascorbic acid, 2,3-diketogulonic acid and oxalic acid (Fig 2). The main route of elimination of ascorbic acid and its metabolites is through urine. It is excreted unchanged when high doses of ascorbic acid are consumed. Ascorbic acid is generally non-toxic but at high doses (2–6 g/day) it can cause gastrointestinal disturbances or diarrhea [10,11]. The side effects are generally not serious and can be easily reversed by reducing intake of ascorbic acid. Furthermore, there is no consistent and compelling data on serious health effects of vitamin C in humans [11].
A deficiency of ascorbic acid (vitamin C) leads to scurvy. It is characterized by spongy swollen bleeding gums, dry skin, open sores on the skin, fatigue, impaired wound healing and depression [13]. Scurvy is of rare occurrence nowadays due to adequate intake ascorbic acid through fresh vegetables and fruits and or supplementation as tablets.