To evaluate the time-dependent degradation rate of riboflavin after ultraviolet A (UVA) irradiation.
Two solutions of commercially available riboflavin solution (0.1%) were used; one served as control, while the second was irradiated using UVA light at 370 nm wavelength. Four samples of riboflavin solution were retrieved prior to irradiance and at 1, 5, 15, 30, and 60 minutes after irradiation (group A); at the same time points samples of riboflavin were retrieved from the control solution in order to assess environmental time-induced degradation of riboflavin (group B). All samples were immediately analyzed using liquid chromatograph mass spectrometry to detect riboflavin and its 2 subproducts, lumiflavin (LF) and lumichrome (LC).
Mean percentage of riboflavin degradation was 0.0, 5.3, 9.1, 15.3, 20.6, and 33.3 at 0, 1, 5, 15, 30, and 60 minutes after UVA irradiation, respectively (group A). The time-dependent riboflavin degradation was statistically significant (p<0.05), while for group B there was no change in riboflavin concentration at all time intervals. In group A, mean LC concentration demonstrated a gradual concentration increase, reaching 2.386±1.526 ppm after 60 minutes of UVA exposure.
The time-dependent degradation of riboflavin solution is significant, reaching 20.6% after 30 minutes of UVA exposure. It seems that only a small fraction of the overall riboflavin molecules break down since more than 65% remain intact even after 1 hour of UVA irradiation. Control riboflavin solution seems to be stable, as no degradation is evident even after 60 minutes.