REACTIVITY OF DIETARY PHENOLIC-ACIDS WITH PEROXYL RADICALS - ANTIOXIDANT ACTIVITY UPON LOW-DENSITY-LIPOPROTEIN PEROXIDATION

The interaction of four phenolic acids, representative of three chemic al groups present in human diet, with peroxyl radicals was studied in vitro in a low density lipoprotein (LDL) oxidation model. The controll ed oxidation of LDL was initiated by free radicals generated from a hy drophilic azo initiator and followed by monitoring the oxygen consumpt ion and the fluorescence quenching of cis-parinaric acid previously in corporated into LDL. The hydroxycinnamic acid derivatives, chlorogenic and caffeic acids, have high stoichiometric numbers and reactivity wi th peroxyl radicals as compared with trolox, the water-soluble analogu e of vitamin E, whereas ellagic acid (a tannic compound) compares with trolox effects. Protocatechuic acid (a hydroxybenzoic acid derivative ) exhibits a complex reaction with peroxyl radicals, as indicated by U V spectroscopy, resulting in undefined inhibition periods of LDL oxida tion and low reactivity with peroxyl radicals. Presumably, secondary r adicals of these compounds are unable to initiate LDL oxidation. The a ntioxidant activity of the various phenolic compounds is discussed in terms of structure-activity relationships.