14B-21

L. YANG, College of Chemistry and Enviromental Science, Henan Normal University, Xinxiang, Henan, China and Z. Y. Chen, Department of Biochemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong, China.

CLA is an anticarcinogen. There has been increasing interest in commercializing CLA as an animal feed additive and food ingredient for humans. The objective of the present study was to study the thermal stability of individual CLA isomers. The oxidation was conducted at 47^oC and 90^oC and haptadecanoic acid was used as an internal standard. The individual CLA isomers were separated and quantified using gas-liquid chromatography (GLC) and silver-ion high-performance liquid chromatrography (Ag-HPLC).

CLA as a mixture of isomers was extremely unstable to the same extent as docosahexaenoic acid, but it oxidized considerably faster than linolenic acid and linoleic acid. When CLA isomers were grouped by configuration of their double bonds, it was found that cc-isomers (c,c-11,13-CLA, c,c-10,12-CLA, c,c-9,11-CLA and c,c,8,10-CLA) were most unstable followed by c,t-isomers (c,t/t,c-11,13-CLA, c,t/t,c-10,12-CLA, c,t/t,c-9,11-CLA and c,t/t,c-8,10-CLA). In contrast, t,t-isomers (t,t-11,13-CLA, t,t-10,12-CLA, t,t-9,11-CLA and t,t-8,10-CLA) were relatively stable. The mechanism by which CLA decomposed readily was probably due to its resonance structure and easier loss of an electron to form the unstable free-radical intermediate.