Impact of microbial cultures on conjugated linoleic acid in dairy products—a review

Abstract

The conjugated linoleic acid (CLA) isomers present in milk fat have a high health amelioration potential. Their high prevalence in fat of ruminants and in milk and dairy products has been described and confirmed over many years. The CLA isomers are formed during biohydrogenation of linoleic acid in the rumen and also through conversion of vaccenic acid in the mammary gland. In addition, several strains of Lactobacillus, Propionibacterium, Bifidobacterium and Enterococcus are able to form CLA from linoleic acid and thus could be used to increase the CLA level in fermented dairy products such as yoghurt and cheese. It appears likely that lactic acid bacteria and especially propionibacteria can form CLA during cheese ripening because free linoleic acid is formed in the ripening process. However, for the time being the reviewed data allow no final conclusion on whether these increased levels of CLA are mainly due to formation by microorganisms, or due to cattle feed or breed. Further studies including all these parameters will be necessary to elucidate the potential role of starter cultures to achieve physiologically relevant CLA levels in dairy products. It appears that contribution of presently used dairy starter bacteria to increased CLA content in cheese is relatively minor.