Stability and Stabilization of Ascorbic Acid
Ascorbic acid (vitamin C) is extensively used in a variety of formulations including creams. It is an ingredient of anti-aging cosmetic products alone or along with alpha-tocopherol (vitamin E). In solutions and creams, ascorbic acid is susceptible to air and light and undergoes oxidative degradation to dehydroascorbic acid and further to inactive products. The degradation is influenced by oxygen, temperature, viscosity and pH of the medium and is also catalyzed by metal ions, particularly Cu2+, Fe2+, and Zn2+. This review highlights the stability and modes of stabilization of ascorbic acid in both the cosmetic and pharmaceutical preparations. A number of approaches involved in the stabilization of the vitamin such as the use of antioxidants, stabilizers, synergists, other vitamins, and formulation of multiple emulsions, nanosuspensions, microencapsulation, etc. have been discussed.
Ascorbic acid (AA) is known to play an important role as an antioxidant due to its presence in the body fluids (1). It causes an increase in the rate of absorption of iron, calcium and folic acid and hence reduces allergic reactions, boosts the immune system, stimulates the formation of bile in the gallbladder and facilitates the excretion of various steroids (2). In the body AA plays an essential role in the production of collagen tissue around bones, teeth, cartilage, skin and damaged tissue (3). It has shown a prominent pharmacological effect in a number of disease conditions such as scurvy, common cold, osteoarthritis, hypertension, heart diseases, cancer, diabetes mellitus, asthma, wound healing, pregnancy, gout and eye diseases (4). Because of all these favourable effects, AA has been used in a variety of cosmetic and pharmaceutical formulations (5). It is highly soluble in water and alcohol, and is easily oxidised to dehydroascorbic acid in its solubilised form (1). The rapid degradation of AA in aqueous media is still a major factor in the formulation of its products. It is also reported that AA oxidation occurs rapidly in an alkalin ...