Improved Method for Preparation of the Methyl Ester of Conjugated Linoleic Acid

Abstract

The authors established a simple method for conducting the quantitative analysis of conjugated linoleic acid using BF₃-methanol solution as methylation reagent. Following the addition of 25 mg of conjugated linoleic acid to 2 mL 14% BF₃-methanol solution and heating for 10min at 40°C, there appeared tp be no significant isomerization of CLA to t,t-isomers or production of methoxy artifacts. Triglyceride containing CLA (25 mg), was saponified with 1.5 mL 0.5 M NaOH-methanol solution for 7 min at 100°C and to which 2 mL 14% BF₃-methanol solution were added followed by heating for 10 min at 40°C. CLA recovery, measured using heptadecanoic acid as internal standard, was 99.7±0.3% (n=3) and 99.7±0.4% (n=3), when analyzed in free fatty acid and triglyceride forms, respectively. The present improved method for preparing the methyl ester of conjugated linoleic acid would thus appear useful for the quantitation of CLA in foods.