The Photolysis Mechanism of Riboflavin in Milk Serum : The Correlation Between the Superoxide and Riboflavin Decomposition

Abstract

The photolysis mechanism of riboflavin (RF) in milk serum was studied. When milk serum was light-illuminated, the decomposition of RF in the serum was accelerated. Superoxide anion (O₂^-) and hydrogen peroxide (H₂O₂) were found to form during the illumination, while superoxide dismutase (SOD) activity could not be detected in the milk serum. The decomposition of RF was significantly inhibited by the addition of tryptophan or mannitol which are scavengers of the hydroxyl radical. Conversely, addition of Fe³⁺ or lactoferrin promoted the decomposition.
These results strongly suggest the direct participation of the hydroxyl radical in the RF decomposition in milk serum during light-illumination. It was also suggested that the hydroxyl radical was formed via the iron catalyzed Haver-Weiss reaction in which iron reacts with O₂^- and H₂O₂, although it is still unknown how O₂^- and H₂O₂ were generated by illumination.