ANTIOXIDANT PROPERTIES OF NOVEL TETRAOXYGENATED PHENYLINDAN ISOMERS FORMED DURING THERMAL-DECOMPOSITION OF CAFFEIC ACID

Mild pyrolysis (228 degrees C, 15 min) of rosmarinic, chlorogenic, and caffeic acids increased their antioxidative efficacy in a biological rat liver membrane assay by 4-, 11-, and 460-fold, respectively. The a ctive components in the caffeic acid pyrolysates were identified as th e recently isolated novel tetraoxygenated 1,3-cis- and 1,3-trans-pheny lindan isomers, which showed comparable IC50 values (0.041 and 0.04 mu M, respectively) and were similar to 8-fold more active than butylate d hydroxytoluene (BHT). Comparison of nonroasted, light-roasted, and d ark-roasted coffee extracts showed that the degree of roasting is posi tively correlated to the inhibition of lipid peroxidation in rat liver membranes. The potent reducing properties of the phenylindan isomers resulted in (a) prooxidative effects at relatively higher concentratio ns in an ethyl linoleate peroxidation assay, and (b) promotion of hydr oxylation of 2'-deoxyguanosine to afford 8-oxo-2'-deoxyguanosine. Howe ver, the results of the rat liver homogenate model system show that py rolysis of caffeic acid and its esters chlorogenic acid and rosmarinic acid can procure potent antioxidants and underlines the potential use of heat processing to generate novel bioactive molecules.