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

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Ten phenolic compounds were isolated from a butanol fraction of sage extracts. Their structures were determined by spectral methods (NMR, MS, IR). Among them, a novel compound, 4-hydroxyacetophenone-4-O-β-D-apiofuranosyl-(1f6)-O-β-D-glucopyranoside, was identified. Two test systems, DPPH free radical scavenging activity and radical cation ABTS •+ scavenging activity, were used to evaluate their antioxidant activity. The most active compounds were found to be rosmarinic acid and luteolin-7-O-β-glucopyranoside.

(-)-Epigallocatechin-3-gallate (EGCG), the most abundant and biologically active compound in tea, has been extensively studied for its activities related to disease prevention in animal models and in vitro. However, its stability under different experimental conditions has not been well-characterized. In the present study, the stability of EGCG in animal drinking fluid and under cell culture conditions and the factors that affect its stability under these conditions were investigated. Our results demonstrated that auto-oxidation and epimerization are the two major reactions causing the instability of EGCG. The structures of the major oxidation products, EGCG dimers, were identified. The rates of these reactions were affected by the temperature, pH, the partial pressure of oxygen, the level of antioxidants, the concentration of EGCG, and other components of tea. In future studies with EGCG, its stability should be considered in order to avoid possible artifacts.