Estimation of free radical-quenching activity of leaf pigment extracts.

The chromogen 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) radical (ABTS.+) can be directly generated by the enzymatic system formed by hydrogen peroxide and horseradish peroxidase in ethanolic media. The reaction is time- and concentration-dependent, and the ABTS.+ generated shows excellent stability. The method is an adaptation of the decolouration method previously reported (Cano et al. 1998. Phytochem Anal 9:196-202), which was used for estimating anti-oxidant activity in aqueous media. When the assay described here was used to quantify the anti-oxidant activity of two anti-oxidants, Trolox (an analogue of vitamin E) and beta-carotene, the latter had 2.5 times better anti-oxidant capacity than Trolox at the same concentration. The free radical quenching activity (anti-oxidant activity) of leaf pigment extracts was measured and related to the the carotenoid contents in leaf extracts of barley, oat and citrus. The possibilities of using this experimental approach to evaluate the status of photoprotective pigments are discussed.