On the mechanisms of cyclic and bicyclic fatty acid monomer formation in heated edible oils

Using recent literature data reporting definite chemical structures for cyclic fatty acid monomers (CFAM), we present new insights into cyclization and rearrangement mechanisms that may be involved in the formation of CFAM and their further transformation into bicyclic fatty acid monomers (BFAM) during the frying process. The existence of structural similarities between CFAM and the unsaturated fatty acids from which they were formed, and between structurally related BFAM and CFAM, led us to examine various possible concerted reactions and thermal rearrangements. These structural similarities as well as the limited number of isomers formed provide evidence for concerted routes that are concordant with all identified structures formed from oleic, linoleic and linolenic acids. The proposed reaction pathways account for the presence of BFAM as well as their most probable structures.