trans-10,cis-12-Conjugated Linoleic Acid Isomer Exhibits Stronger Oxyradical Scavenging Capacity thancis-9,trans-11-Conjugated Linoleic Acid Isomer

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Abstract
Although studies have been performed to test whether conjugated linoleic acid (CLA) acts as an antioxidant, the results were not conclusive. In addition, the CLA widely used in previous research contains 43% cis-9,trans-11 isomer, 45% trans-10,cis-12 isomer, and 10 other minor isomers. The objective of this study was to investigate the antioxidant activity of cis-9,trans-11- and trans-10,cis-12-CLA isomers using high-purity CLA isomers (>98%) by total oxyradical scavenging capacity assay (Winston, G. W.; Regoli, F.; Dugas, Jr., A. J.; Fong, J. H.; Blanchard, K. A. Free Radical Biol. Med. 1998, 24, 480−493). At all concentrations (2−200 μM), t10,c12-CLA performed as an antioxidant with a 15-min lag phase, which was more effective than c9,t11-CLA and α-tocopherol at lower concentrations (2 and 20 μM). On the other hand, c9,t11-CLA possessed weak antioxidant activity at 2 and 20 μM, whereas at 200 μM it acted as a strong pro-oxidant, which suggests that discrepancies of the results of the previous studies on the antioxidant properties of CLA may be due to the balance of the antioxidant properties of t10,c12-CLA and the pro-oxidant properties of c9,t11-CLA in different oxidation conditions. Keywords: Conjugated linoleic acid; antioxidant; TOSC assay