Influence of processing on the fatty acid composition and the content of conjugated linoleic acid in organic and conventional dairy products - a review

An overview of the present knowledge on the influences of dairy processing and storage on the content of conjugated linoleic acids ( CLA) and to possible differences between organic and standard products is given. In organic dairy products CLA was reported to be from not significantly up to 135% higher. Newer studies on the effect of heating steps show no changes in CLA content or isomer profiles, with the exception of microwaving, where CLA was decreased by up to 53%. In commercial dairy products no effects of fermentation on CLA content were observed. Recent studies on cheese showed no changes in the CLA content during manufacturing or ripening. CLA content was stable during butter-making out of CLA-enriched milk. In several more recent investigations with probiotic bacteria ( lactic acid bacteria such as Lactobacillus rhamnosus or Lactobacillus acidophilus, and propionibacteria and bifidobacteria such as B. breve and B. dentium) or other strains of these bacteria groups on a laboratory scale, an increase in CLA could be observed under the condition that free linoleic acid ( LA) was available in the culture medium. Conversion rates reached up to 87% with Propionibacteria freudenreichii ssp. shermanii. In cultivated form, B. breve reached a comparably high concentration of 398 mg CLA . L-1 broth. Especially high concentrations of up to 40 g CLA . L-1 broth could be produced with resting cells of Lactobacillus plantarum and Lb. acidophilus or with immobilised cells of Lb. delbrueckii ssp. bulgaricus. CLA formation in yoghurt could be observed under the condition that free LA was added. After 14 days of storage the increase was 77%. Specific procedures allow one to increase the content of CLA in a fraction. These procedures are dry fractionation (63% increase), fractionation using supercritical carbon dioxide (89% increase) and crystallisation ( concentration 2.5 times). Numerous studies on the shelf-life stability of CLA-enriched dairy products showed no significant differences in flavour quality parameters.