Overview of conjugated linoleic acid formation and accumulation in animal products

In this review, we provide an overview of the methods used to enhance conjugate linoleic acid (CLA) in animal products and the mechanisms through which CIA is synthesized or accumulated in animal products. Linoleic acid is the key precursor of CIA; thus, CIA can be synthesized through conversion of linoleic acid by ruminal bacteria (Propionibacterium) and lactic acid bacteria (Lactobacillus, Lactococcus, and Streptococcus) with biohydrogenation. Accordingly, it is possible to increase the CIA concentrations in meat, milk, or eggs from animals through feeding of a polyunsaturated fatty acid-rich diet, e.g., a diet containing linoleic acid. Dietary green grass enhances the growth of specific rumen bacteria that are responsible for the synthesis of CIA in animals. CIA or linoleic acid intake increases CIA concentration in dairy products such as milk, cheese, and yogurt. In order to increase CIA status in humans, probiotic bacteria that can be used to convert dietary linoleic acid to CIA. However, it is unclear how much CIA needs to be consumed to have appropriate benefit on human health. Thus, future research is needed to establish methods for controlling the amounts of CIA and CIA isomers in animal products and to determine the exact mechanisms of CIA consumption on human health.