Effect of fatty acid positional distribution and triacylglycerol composition on lipid by-products formation during heat treatment:: II.: Trans isomers

This study examined the effect of the fatty acid positional distribution and of the triacylglycerol (TC) composition on heat-induced trans isomerization of linoleic and linolenic acids. For this, we synthesized diacid TG molecules that were acylated only with linoleic acid (L) or with linolenic acid (Ln) along with palmitic acid (P). The fatty acid of interest was positioned either in the central position (PLP and PLnP, respectively) or in one of the two outer positions (PPL and PPLn, respectively). Monoacid TG, i.e., trilinolein and trilinolenin, were also synthesized and mixed with tripalmitin in a 1:2 ratio. This model TG was also compared to another TC model, which consisted of a canola oil and its randomized counterpart whose fatty acid positional distribution and TC composition were determined by means of high-performance liquid chromatography. After heating, the content of trans isomers was determined by gas-liquid chromatography with a polar capillary column. In model TG, polyunsaturated fatty acids in monoacid TC (LLL acid LnLnLn) exhibited the highest degree of isomerization, compared to diacid TC, and this effect was greatest at 220 degrees C At this temperature, an effect of the TG structure was observed only with linolenic acid. In that situation, 18:3n-3 acylated in the central position of the TG molecule (PLnP) displayed the highest sensitivity to trans geometrical isomerization. Although to a lesser extent, the same trends as for the pure TC model were observed with the canola oil model with regard to the influence of the fatty acid positional distribution and TC molecular species.