Factors affecting formulation characteristics and stability of ascorbic acid in water-in-oil creams.

The present investigation is based on the formulation of water-in-oil (w/o) cream preparations of ascorbic acid (AA) at pH 4-6 using different emollients and humectants. The preparations were stored in the dark at 30°C for a period of 3 months and were studied for their chemical and physical stability. The pH of the creams appeared to influence the stability of AA as the degradation was found to increase with an increase in pH. The degradation of AA in w/o creams followed an apparent first-order kinetics. Among all the preparations, the creams containing castor oil as emollient and glycerine as humectant showed highest viscosity and minimum degradation as compared with the creams containing other excipients. This indicated that higher the viscosity of the medium lower will be the degradation of AA. Citric acid (CT) was found to decrease the rates of degradation of AA in all the cream preparations. The physical mixtures of AA and CT showed no interaction between the two compounds by FTIR spectrometry indicating that the reduction in rates of degradation is due to the antioxidant activity of CT which protected AA to some extent from the atmospheric oxygen.