The effect of the methylation method on isomerization of conjugated linoleic acid (CLA) in gas chromatographic analysis was studied. Among methylation methods examined, the magnitude of isomerization of CLA was greatest with BF 3 catalyst, followed by HCl and H 2 SO 4 catalyst. Shorttime methylation did not extensively change the CLA composition in all methods, and c,t and t,c isomers were essentially maintained, while the appearance of t,t isomers and unknown peaks was practically restricted. After 120 min of methylation, there was essentially no conversion in the H 2 SO 4 method, in contrast to a marked change in the BF 3 method. The antioxidants butylated hydroxytoluene, ascorbic acid, β-carotene, and α-tocopherol did not suppress conversion, while dimethylsulfoxide (DMSO) and dimethylformamide (DMF) attenuated the changes in CLA composition. Suppression was more effective in the H 2 SO 4 method than in the BF 3 method. Thus, methylation with H 2 SO 4 in the presence of a proper amount of DMSO or DMF is recommended for esterification of CLA.Paper no. J9018 in JAOCS 76, 933-938 (August 1999).
The dietary effects of conjugated linoleic acid (CLA) on Ig production of Sprague-Dawley rats were examined at various doses such as 0 (control), 0.05, 0.10, 0.25, and 0.50%. CLA increased IgG and IgM production of spleen lymphocytes in a dose-dependent manner, and these levels reached a plateau at 0.25%. IgA production was not detected in the control group, while it was detected in all CLA-fed groups and IgA productivity of spleen lymphocytes increased in a dose-dependent manner at the doses from 0.05 to 0.50%. Dietary CLA did not affect serum Ig levels. The major fatty acid composition of spleen lymphocytes was not affected by dietary CLA, which itself was hardly incorporated into the cells. In an in vitro assay, the effects of CLA and its oxidative derivatives, furan type fatty acids, on Ig productivity were also examined. As a result, 100 microM CLA suppressed Ig production of spleen lymphocytes and the degree was as follows IgA > IgG > IgM. Each CLA isomer and the furan type fatty acids also suppressed Ig production but the degree was weaker than the mixture of CLA isomers. In this result, dietary CLA increased Ig productivity of spleen lymphocytes in vivo.
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