Oxidation rate of conjugated linoleic acid and conjugated linolenic acid is slowed by triacylglycerol esterification and alpha-tocopherol

We have recently shown that α‐eleostearic acid (α‐ESA), a conjugated linolenic acid, has a stronger antitumor effect than conjugated linoleic acid (CLA), both in vitro and in vivo. In this study, the oxidative stability of α‐ESA was examined compared with linoleic acid (LA), α‐linolenic acid (LnA), and CLA. Thin layers of the FA (LA, 9Z, 11E‐CLA, 10E,12Z‐CLA, LnA, and α‐ESA) were auto‐oxidized at 37°C, and the FA remaining, the absorbed oxygen volume, the lipid hydroperoxide content, and the TBARS content were determined. The oxidation rate of α‐ESA was faster than that of the unconjugated FA and CLA (9Z,11E‐CLA and 10E,12Z‐CLA). However, the lipid hydroperoxide and TBARS contents following α‐ESA oxidation were low, suggesting production of only small amounts of rapid‐reacting secondary oxidation products. Furthermore, the oxidative stability of conjugated FA (CLA and CLnA) in which the carboxylic acid group was esterified with triacylglycerol was greater than that of the FFA. Addition of an antioxidant (α‐tocopherol) also increased the stability of the conjugated FA to a level similar to that of the unconjugated FA.