Crystal structures and melting points of unsaturated triacylglycerols in theβphase

Abstract

The/3-phase crystal structures of unsaturated triacylglycerols (TAGs) have been analyzed. Long spacings and melting points of monounsaturated TAGs such as 16" O. 16 and 16.0" 18 indicate a fi-3C packing mode with a methyl terrace that differs from that of the saturated /3-3 TAGs. In addition to the hydrocarbon chain subcell packing and the methyl terrace structure, the conformation of the oleoyl chain also has to be considered. This conformation is analyzed in connection with the symmetry relation between the two half-layers on either side of the plane through the double bonds. Geometric analysis shows four possibilities, which have been explored further by means of energy minimization computations. In these calculations the structure of the oleoyl chain, in its crystalline environment, has been optimized while taking all relevant intramolecular and intermolecular forces into account. Though the calculations reveal relatively small energy differences between the four possibilities, the most likely structure can still be identified. On the basis of the results obtained for the monounsaturated TAGs, proposals for the crystal structures of diunsaturated (e.g., 0 9 18. O) and triunsaturated (e.g., 0" 0" O) TAGs are briefly outlined.

Structural models of metastable phases occurring during the crystallization process of saturated/unsaturated triacylglycerols

“…1 and 2). Assuming that the structure has a symmetry which is typical in the structural organization of TAGs and lipids (de Jong et al, 1991;Small, 1986), then 16 different variants (= 2 4 ) of phase signs of amplitudes in equation (1) and, therefore, 16 variants of S 0 (z) could be obtained from the amplitudes. All these variants can be subdivided into four groups (see Fig.…”

Effect of unsaturated acyl chains on structural transformations in triacylglycerols

“…Finally, the matching of the terminal methyl groups within the inter-layer space and the conformational order of unsaturated bonds, when such are present, completes the polymorphic transformation to the most stable b-phase with a parallel packing of the acyl chains in the subcell unit (Fig. 1f) [8][9][10].…”

Alpha stable fats

“…Consequently there is a magnitude of different triacylglycerols available and depending on size and shape they have different preferences when it comes to crystal packing. For example systems consisting of a lot of symmetric triacylglycerols, that is trisaturated fractions or cocoa butter fats, can crystallize in the highly arranged, tightly packed beta polymorph (1). Systems consisting of asymmetric triacylglycerols on the other hand are unable to form beta crystals on their own and beta' (beta prime) crystals are their preferred state (1).…”

“…For example systems consisting of a lot of symmetric triacylglycerols, that is trisaturated fractions or cocoa butter fats, can crystallize in the highly arranged, tightly packed beta polymorph (1). Systems consisting of asymmetric triacylglycerols on the other hand are unable to form beta crystals on their own and beta' (beta prime) crystals are their preferred state (1). Furthermore, triacylglycerols having one fatty acid chain differing greatly from the other two prefer triple chain packing instead of the common double-chain packing.…”