Evaluation of the antioxidant activity and partial characterisation of extracts from browned yam flour diet

The antioxidant activity of the ethyl acetate extract of browned yam flour, a diet widely consumed in West Africa especially in southern part of Nigeria, was examined in beta-carotene linoleate system and egg yolk phosphatidyl choline (EYPC) liposomal membrane exposed to the lipid soluble 2,2-azobis (2-amidinopropane) hydrochloride (AAPH) generated peroxyl radicals. Total antioxidant activity (TAA) of crude ethyl acetate extract was determined using 2,2' azinobis- (3-ethyl benzothiazoline-6-sulfonic acid) (ABTS) and Horseradish peroxidase as enzyme source. TAA of the extract was estimated to be 7.5 measured as mM of Vitamin C equivalent. The crude extract was fractionated on a sephadex LH-20 column using methanol as eluant at a flow rate of 1.8 ml/min. Fractions 1, 2 and 3 showed similar absorption maxima in the range of 190-230 and 240-269. Fractions 4-7 produced absorption maxima in the range of 270-280. Although, the crude extract showed a higher antioxidant effect than butylated hydroxyanisole (BHA), all the isolated fractions exhibited a lower antioxidant activity than BHA in the beta-carotene linoleate model system. Compared to control, fractions 2, 3, 5 and 6 showed good antioxidant effect against the bleaching of beta-carotene. Incorporation of the fractions into EYPC liposomes retarded the lipid peroxidation caused by AAPH derived peroxyl radicals to varying extents. Fractions 2, 3, 5 and 6 significantly (P < 0.001) reduced AAPH mediated thiobarbituric acid reactive substances (TBARS) formation. Partial characterisation of this extract by TLC on silica gel plates showed that fractions 5 and 6 contain several phenolic compounds. TLC and UV/visible data suggest that fractions 2 and 3 may contain browning reaction products such as pyrazines and acetylfurans. The results of the present investigation suggest that browned yam hour contains natural antioxidants and as such may mediate in oxidative damage and diseases caused by environmental chemicals. (C) 2000 Elsevier Science Ltd. All rights reserved.