2020-Molecular formation mechanism of trans linolenic acid in thermally induced α-linolenic acid
The isomerization mechanism of thermally inducedα-linolenic acid (C18:3-9c,12c,15c) was investigated using a combination of experimental and computational studies. C18:3-9c,12c,15c in linseed oil and trilinolenin was heated at 180, 240, and 260 °C for 4 and 8 h and then analyzed by GC-MS. Mono-trans isomers easily formed from C18:3-9c,12c,15c, and then became double- and triple-trans isomers in heated linseed oil and trilinolenin. Six pathways of C18:3-9c,12c,15c isomerization via proton transfer were proposed and clariﬁed. The hydrogen in the C9, C12, and C16 of the double bonds in C18:3-9c,12c,15c more favorably transferred to C10, C13, and C15, respectively, where the C9–H9 transfer occurred more quickly than C12–H12 and C16–H16 during isomerization. The formation of the mono-trans isomers was slower than the double- and triple-trans isomers, and the activation energies of the transition and rotate-transition states of the mono-trans isomers were the key factors inﬂuencing the formation of trans C18:3 isomers. Density functional the orycalculations demonstrated the experimental data obtained was consistent with the proposed proton transfer isomerization mechanism.