Evaluation of potential interfering agents on in vitro methods for the determination of the antioxidant capacity in anthocyanin extracts

The evaluation of the effects of sugars, metals, acids and other antioxidants on the in vitro antioxidant capacity of purified anthocyanin extract by different techniques was the purpose of this study. Three methods and the ways of expressing their results were evaluated: ABTS(TEAC) (capacity equivalent to Trolox, by ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid))), DPPHTEAC (capacity equivalent to Trolox, by DPPH (2,2-diphenyl-1-picrylhydrazyl)), DPPHEC50 (50% reduction in the radical, by DPPH), DPPH%Sca (reduction in the scavenging capacity, by DPPH), FRAP(TEAC) (capacity equivalent to Trolox, by FRAP (reduction power of iron)) and FRAP(EC50) (50% reduction in the radical, by FRAP). The way of expressing DPPH and FRAP results as EC50 showed the greater interfering extent, mainly when the medium contained tartaric and ascorbic acids. The most coherent method was ABTS(TEAC) in which only ascorbic acid interfered. Ascorbic acid was shown to interfere in all methods; thus, it must be removed prior to determining the in vitro antioxidant capacity of anthocyanins in food materials.