Analysis of conjugated linoleic acid isomers and content in french cheeses

Conjugated linoleic acid (CLA) occurs in food as a result of microbial enzymatic reactions, free radical-type oxidation, and heat treatment. CLA is found in animal products, such as meat and dairy products, especially in cheeses. The CLA composition of 12 different French cheeses was determined by a combination of different analytical methods: reversed-phase high-performance liquid chromatography (RP-HPLC), gas chromatography-mass spectrometry (GC-MS), GC-Fourier transform infrared (GC-FTIR), and silver nitrate thin-layer chromatography (AgNO₃-TLC). New isomers (Δ8,10- and Δ11,13-octadecadienoic acids with all possible cis and trans configurations) that co-eluted with previously identified isomers (Δ9c,11t-; Δ9t,11c-; Δ10c,12t-; Δ10t,12c-; Δ11c,13c-; Δ9c,11c-; Δ10c,12c-; Δ9t,11t-; Δ10t12t-octadecadienoic acids) were detected. Δ9c,11t-Octadecadienoic acid was the major CLA isomer in these cheeses. All isomers were present in each product, whatever the production process. However, CLA content in the cheeses varied from 5.3 to 15.80 mg/g of cheese fat, which depended primarily on the origin of the milk (season, geography) and somewhat on the production process.