We found that the oxidation of cyanidin with hydrogen peroxide, tert-butyl hydroperoxide, 2,2'-azobis(2-methylpropionamidine), 3-morpholinosydnonimine hydrochloride, sodium hypochlorite, Fe3+, and Fe2+ induced the appearance of a new fluorescence band, centered at 525-540 nm when excited at 470-490 nm. The intensity of this fluorescence was related to the oxidant concentration. The same fluorescence was induced by the oxidation of other anthocyanidins, an anthocyanin (cyanidin-3-O-glucoside) as well as anthocyanin-rich red cabbage extract, and blackcurrant and elderberry juices. Peroxidized blood plasma also induced the appearance of cyanidin fluorescence. We also showed that the formation of the fluorescent product of pelargonidin can be observed in a culture of the MRC-5 human fetal lung fibroblast cell line and the DU-145 human prostate carcinoma cell line. Our results suggest that this new anthocyanidin/anthocyanin fluorescence may be an indicator of oxidation, especially of food products, where these compounds are present or added as colorants, and can also be useful to detect oxidation in biomedical experiments.
Keywords: anthocyanidins; anthocyanins; cyanidin; hydrogen peroxide; oxidation.