ARE WHOLE EXTRACTS AND PURIFIED GLUCOSINOLATES FROM CRUCIFEROUS VEGETABLES ANTIOXIDANTS

Fruits and vegetables contain several classes of compounds that can po tentially contribute to antioxidant activity, including vitamins, simp le and complex phenolics, sulphur-containing compounds and glucosinola tes. The glucosinolates are found in high concentration in many crucif erous vegetables, and it is well established that their breakdown prod ucts induce endogenous antioxidant defences such as quinone reductase and glutathione S-transferase in cells and in vivo. Despite the antica rcinogenic effect of these compounds in animal models, the direct anti oxidant properties of this class of compounds have not been systematic ally studied. We therefore examined the free radical-scavenging proper ties of representative extracts and of purified glucosinolates from cr uciferous vegetables, by measuring their effect on ascorbate- or NADPH /iron-induced peroxidation of human liver microsomes, ascorbate/iron-i nduced peroxidation on phospholipid liposomes, iron chelation and hydr oxyl radical scavenging using the deoxyribose assay, total antioxidant potential using ABTS 2'-azinobis(3-ethyl-benzothiazoline-6-sulphonate )) and the bleomycin assay. Most of the extracts from cruciferous vege tables exhibited some antioxidant properties, although extracts from c ooked Brussels sprouts increased the rate of microsomal lipid peroxida tion. The effects in these assays were dependent upon processing and s pecies of crucifer, and the glucosinolate content appeared to play a m inor role in these effects, since purified glucosinolates exhibited on ly weak antioxidant properties. The total antioxidant activities of ex tracts from cooked and autolysed Brussels sprouts were identical withi n experimental error. This is probably due to the content of phenolics which is unaltered by autolysis, despite the differences between thes e samples in other assays especially NADPH-iron-induced lipid peroxida tion of human liver microsomes. The results demonstrate that glucosino lates are unlikely to account for the direct antioxidant effects of ex tracts from cruciferous vegetables.