Synthetic methods to obtain conjugated linoleic acids (CLAs) by catalysis – A review

Abstract

The addition of synthetic CLA is a possible way in order to compose foods enriched with conjugated linoleic acids (CLAs). The most environmental friendly methods for CLA synthesis are based on microbial biosynthesis. With homogeneous catalysis using organometallic catalysts (Ru and Rh complexes) high (approximately 80%) yields were obtained with high selectivity related to bioactive isomers. The heterogeneous catalysis has the advantage that at the end of the reaction there is no need for a supplementary separation operation or recycling of the catalyst. In heterogeneous process, the maximum yield may even be higher than 90% and the selectivity remains quite high as the reaction conditions are optimized. The substrates for obtaining CLAs are, in general, linoleic acid or alkyl linoleates and the catalysis is acidic. The yield and the selectivity depend on the strength and the type of acidic sites, as well as on the size distribution of the particles. Beside the existing catalytic methods, a photocatalytic process with UV and visible light irradiation with iodine promoter can be applied.