Effect of fatty acid positional distribution and triacylglycerol composition on lipid by-products formation during heat treatment: III - Cyclic fattyacid monomers study

The influence of isomeric triacylglycerols (TG) containing 18:3n-3 and 18:2 n-6 on the formation of cyclic fatty acid monomers (CFAM) after heat treatm ent was assessed. Diacid TG, containing linoleic acid (L) or linolenic acid (alpha-Ln) along with palmitic acid (P), and positioned either in the cent ral position (PLP and PLnP, respectively), or in one of the two outer posit ions (PPL and PPLn, respectively) were synthesized. Monoacid TG of trilinol ein and trilinolenin mixed with tripalmitin were also prepared. The CFAM fo rmed after heating were analyzed after total hydrogenation. The results obt ained with the model TC were compared to another model consisting of a cano la oil and its randomized counterpart. In diacid TC, the location of alpha- Ln in the central position of the TC molecule (PLnP) greatly enhanced the f ormation of the CFAM upon heating at temperatures below 240 degrees C. On t he other hand, 18:3n-3 in monoacid TG (LnLnLn) was highly resistant to CFAM formation within the same range of temperatures (180-220 degrees C). The T C structure, more than the TG composition, seemed to explain the difference s in the CFAM formation between the original canola oil and its interesteri fied counterpart. Like alpha-Ln, 18:2n-6 was more prone to cyclization when attached at the central position of the model TC. Conversely, the influenc e of the TG composition on the cyclization rate was less important for L th an for alpha-Ln. It was concluded that positioning the C18 polyunsaturated fatty acid in the central position of TG rendered the oils much more sensit ive to the cyclization reaction upon heat treatment.