Antioxidant activities of caffeic acid and its related hydroxycinnamic acid compounds

Hydroxycinnamic acid compounds are an important source of antioxidants due to their ubiquitous occurrence in the plant kingdom and their characteristic activities. In this study, we compared the antioxidative and free radical scavenging activities of caffeic acid (CA), caffeic acid phenethyl ester (CAPE), ferulic acid (FA), ferulic acid phenethyl ester (FAPE), rosmarinic acid (RA), and chlorogenic acid (CHA) with those of alpha-tocopherol and BHT. In the Rancimat test, the addition of test compounds in lard significantly extended the induction time of lipid oxidation, and the activities in decreasing order were CA similar to alpha-tocopherol > CAPE similar to RA > CHA >> BHT > FA similar to FAPE. When the lipid substrate was changed to corn oil, the effectiveness of antioxidants on the induction time was obviously decreased, and the potency order of antioxidants was changed to RA > CA similar to CAPE similar to CHA > alpha-tocopherol > BHT; FA and FAPE had no significant antioxidative effect in the corn oil system. The 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging activity of the test compounds was RA >> CAPE > CA > CHA > alpha-tocopherol > FA > FAPE > BHT. The effect on retarding oil-in-water emulsion oxidation was BHT > CA > CAPE > RA > FA > CHA > alpha-tocopherol > FAPE, and the incubation times to reach an absorbance of 0.4 by the ferric thiocyanate method were 14.4, 11.4, 8.6, 7.3, 6.4, 4.6, 4.2, and 2.8 days, respectively, with the value of the control around 1.3 days.