Factors Affecting Conjugated Linoleic Acid (CLA) Content in Milk, Meat, and Egg: A Review

An increasing interest in enhancing the conjugated linoleic acids (CLA) content in food products is attributed to its potential anti-carcinogenic, anti-diabetic, anti-obesity, anti-atherogenic, and immunomodulatory functions in experimental animal models. It is synthesized in the rumen from linoleic acid or from the endogenous conversion of t-11 C18:1 in the mammary gland by delta-9 desaturase. More than a dozen isomers of CLA have been detected in foods of ruminant origin, of which c-9, t-11 comprising 80 to 90%, and t-10, c-12 comprising 3-5% of total CLA are the isomers with known physiological importance. Although food products from ruminants are the richest source of CLA for humans, it is possible to enhance the CLA content of foods from non-ruminants by supplementing CLA in the diet. The CLA content in milk, meat, or egg varies greatly from a low 0.1% or less to a high 2% or more of the milk, tissue, or egg yolk lipids, with milk lipids from ruminants having the highest concentrations. A host of factors appear to affect the CLA content in milk, meat, and other food products from various species of animals, which could be broadly classified into diet, animal, and post-harvest related factors. Of all these factors, animal diet is the primary one and could be manipulated to a great extent for enhancing the concentration of CLA in food products, both from ruminants and non-ruminants. While animal-to-animal variation is also of great significance, post-harvest related factors appear to be of minor importance. In this context, the CLA content of milk, meat, and egg, and the factors affecting its concentration have been reviewed. Understanding the various factors affecting the CLA content in food products will have practical implications to the dairy, meat, or egg producers for its enrichment in food products so we can derive the potential health benefits associated with CLA.