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, esp ecially in cheeses. The CLA composition of 12 different French cheeses was determined by a combination of different analytical methods: reve rsed-phase high-performance liquid chromatography (RP-HPLC), gas chrom atography-mass spectrometry (GC-MS), GC-Fourier transform form infrare d (GC-FTIR), and silver nitrate thin-layer chromatography (AgNO3-TLC). New isomers (Delta 8, 10- and Delta 11, 13-octadecadienoic acids with all possible cis and trans configurations) that co-eluted with previo usly identified isomers (Delta 9c, 11t-; Delta 9t, 11c-; Delta 10t, 12 t-; Delta 10t, 12c-; Delta 11c, 13c-; Delta 9c, 11c-; Delta 10c, 12c-; Delta 9t, 11t-; 12t-octadecadienoic acids) were detected Delta 9c, 11 t-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.