Effect of Boric Acid on the Photostabilization of Ascorbic Acid in Creams Containing Different Humectants and Emulsifiers

In the present work the effect of boric acid (BA) on the stabilization of ascorbic acid (AH(2)) in cream formulations has been studied. The oil-in-water creams of AH(2) (pH 6.0) were prepared and exposed to ultraviolet radiation and also kept in dark at 25 +/- 1 degrees C. The apparent first-order rate constants for the degradation of AH(2) (0.42-1.20 x 10(-3) min(-1) in light, 0.68-1.53 x 10(-2) day(-1) in dark) were determined spectrophotometrically. The second-order rate constants for the interaction of AH(2) and BA (2.61-6.02 x 10(-3) M-1 min(-1) in light, 3.75-5.78 x 10(-2) M-1 day(-1) in dark) indicate inhibitory effect of the stabilizer on AH(2). The rate of degradation of AH(2) in the dark is around 100-150 times slower compared to that of light showing a difference in the mechanism of degradation. The stabilization of AH(2) is affected by humectants, emulsifiers and physical properties of creams.