Quenching mechanism and kinetics of ascorbic acid on the photosensitizing effects of synthetic food colorant FD&C Red Nr 3.

The pH effect on the oxidative stability of ascorbic acid in the presence of food colorant FD&C Red Nr 3 during storage with or without light was investigated. The quenching mechanism and kinetics of ascorbic acid on the FD&C Red Nr 3 photosensitized oxidation in an aqueous system at 25 degrees C were also studied by measuring the degradation of ascorbic acid or depletion of headspace oxygen. Red Nr 3 had no influence on the oxidation of ascorbic acid under dark storage, but accelerated its oxidation rate under light storage. The oxidative stability of ascorbic acid decreased as the pH increased from 4 to 7 under light without FD&C Red Nr 3. The quenching rates of ascorbic acid on the singlet oxygen by measuring the degradation of ascorbic acid in the presence of Red Nr 3 under light storage were 1.53 +/- 0.15 x 10(8), 1.86 +/- 0.25 x 10(8), and 1.19 +/- 0.12 x 10(8) M(-1)S(-1) at pH 4, 5.6, and 7, respectively.