Antioxidant Activities of Caffeic Acid and Its Related Hydroxycinnamic Acid Compounds

TLDR

Hydroxycinnamic acids are widely distributed plant compounds that serve as potent natural antioxidants. The study aimed to compare the antioxidant and free‑radical scavenging activities of caffeic acid, caffeic acid phenethyl ester, ferulic acid, ferulic acid phenethyl ester, rosmarinic acid, and chlorogenic acid with α‑tocopherol and BHT. Activities were assessed by Rancimat induction‑time tests in lard and corn oil, DPPH radical‑scavenging assays, and oil‑in‑water emulsion oxidation measurements. In lard, CA and α‑tocopherol showed the longest induction times, followed by CAPE and RA, with BHT and FA/FAPE least effective; in corn oil, RA was most potent, followed by CA, CAPE, CHA, α‑tocopherol, and BHT, while FA/FAPE had no effect; DPPH scavenging ranked RA ≫ CAPE > CA > CHA > α‑tocopherol > FA > FAPE > BHT; emulsion oxidation was best inhibited by BHT, then CA, CAPE, RA, FA, CHA, α‑tocopherol, and FAPE. Keywords: Antioxidants; caffeic acid; caffeic acid phenethyl ester; free radical scavenging activity; hydroxycinnamic acids.

Abstract

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 α-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 ∼ α-tocopherol > CAPE ∼ RA > CHA ≫ BHT > FA ∼ 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 ∼ CAPE ∼ CHA > α-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 > α-tocopherol > FA > FAPE > BHT. The effect on retarding oil-in-water emulsion oxidation was BHT > CA > CAPE > RA > FA > CHA > α-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. Keywords: Antioxidants; caffeic acid; caffeic acid phenethyl ester; free radical scavenging activity; hydroxycinnamic acids