Photodecomposition of aspartame in aqueous solutions

Photodecomposition of aspartame in aqueous solutions under different conditions of light intensity and pH were studied. The effects of photosensitizers (riboflavin and methylene blue) and ascorbic acid on aspartame stability in aqueous solutions at different pH under light were also studied. Light illumination significantly increased aspartame degradation in an aqueous solution (pH 7), indicating that aspartame was very unstable under the illuminated conditions. In the dark, 91% of aspartame in an aqueous solution at pH 7 remained after 10 h of storage. Under 5500 1x of light, however, 39% of aspartame in the solution was destroyed after 10 h of storage. Aspartame degradation under light followed simple zero-order reaction kinetics. The higher the light intensity, the greater the degradation of aspartame. The relative reaction rate for the destruction of aspartame under 0, 1100, 3300 and 5500 1x was 1:1.42:2.80:4.61. The photodecomposition rate of aspartame varied with the pH of the system. Aspartame degradation was fastest at pH 7.0, followed by pH 4.0 and pH 6.0, in decreasing order. Addition of 4.8 ppm riboflavin or 4.8 ppm methylene blue significantly accelerated the aspartame decomposition at pH 7 in the presence of light. There were, however, no significant photosensitizing effects of these sensitizers on aspartame destruction at pH 6 and pH 4. Addition of 1.2 × 10−4 M ascorbic acid greatly increased the aspartame degradation at pH 7.0, but did not affect the destruction rate of aspartame at pH 6.0 and pH 4.0.