Structure-dependent photodegradation of carotenoids accelerated by dimethyl tetrasulfide under UVA irradiation.

Carotenoids are used in wide-ranging food applications, but they are susceptible to degradation by many factors including light. We examined the photodegradation of five kinds of carotenoids and three kinds of anthocyanins to clarify which structures of pigments were favorable to accelerated degradation by sulfides under UVA irradiation. Under UVA irradiation, crocetin and crocin were decomposed more rapidly in the presence of dimethyl tetrasulfide than in the absence of the sulfide, but not as rapidly as beta-carotene, zeaxanthin and beta-cryptoxanthin were. However, cyanidin was decomposed more slowly in the presence of sulfide than in the absence of sulfide. Moreover, the photodegradation of kuromanin and keracyanin was not affected by the addition of a sulfide. We also examined the mechanism for this accelerated degradation. Normal hexane was more favorable to the photodegradation of beta-carotene than methanol and ethanol. The accelerated degradation was inhibited by free radical scavengers, but enhanced by the addition of deuterium oxide. These results suggest that conjugated double bonds were favorable to the accelerated photodegradation by sulfide and that this reaction was mediated by free radicals.