The relative antioxidant activities, against radicals generated in the aqueous phase, of a range of plant-derived polyphenolic flavonoids, constituents of fruit, vegetables, tea and wine, have been assessed. The results show that compounds such as quercetin and cyanidin, with 3',4' dihydroxy substituents in the B ring and conjugation between the A and B rings, have antioxidant potentials four times that of Trolox, the vitamin E analogue. Removing the ortho-dihydroxy substitution, as in kaempferol, or the potential for electron delocalisation by reducing the 2,3 double bond in the C ring, as in catechin and epicatechin, decreases the antioxidant activity by more than 50%, but these structures are still more effective than alpha-tocopherol or ascorbate. The relative significance of the positions and extents of hydroxylation of the A and B rings to the total antioxidant activity of these plant polyphenolics is demonstrated.

The biological activities [15] of the phenylpropanoids and their role as antimicrobial agents [16,17] is well recognised, as well as their properties as antiallergic and anti-inflammatory agents through lipoxygenase inhibition [18] and their antimutagenic actions [19,20].In this study we have examined the antioxidant properties of the hydroxycinnamic acids in terms of their abilities to increase the resistance of low density lipoproteins (LDL) to cholesterol oxidation, lipid peroxidation and oxidative modification of the apoprotein B,j 0. The results show that the sequence of the effectiveness against lipid peroxyl radicals generated in the lipophilic phase of LDL and in protecting LDL cholesterol from oxidation is: chlorogenic = caffeic > ferulic > p-coumaric acid.

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Two forms of alpha-galactosidase, I and II, exist in Vicia faba seeds and these have been purified 3660- and 337-fold respectively. They behaved as homogeneous preparations when examined by ultracentrifugation, disc electrophoresis and gel filtration. The apparent molecular weights of enzymes I and II, as determined by gel filtration, were 209000 and 38000 respectively. The carbohydrate contents of enzymes I and II were 25% and 2.8% respectively, and the enzymes differed in their aromatic amino acid compositions. Enzyme I was split into six inactive subunits in the presence of 6m-urea. alpha-Galactosidases I and II showed different pH optima and K(m) and V(max.) values with p-nitrophenyl alpha-d-galactoside and raffinose as substrates, and also differed in their thermal stabilities.

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