Binary phase behavior of 1,3‐distearoyl‐2‐oleoyl‐sn‐glycerol (SOS) and 1,3‐distearoyl‐2‐linoleoyl‐sn‐glycerol (SLS)

Abstract

The binary phase behavior of SOS (1,3-distearoyl-2-oleoyl-sn-glycerol) and SLS (1,3-distearoyl-2-linoleoyl-sn-glycerol) was examined by using DSC and conventional and synchrotron radiation X-ray diffraction. The solidsolution phases were observed in the metastable α and γ forms in all concentration ranges. Results indicated that the miscible γ form did not transform to the β′ form when the mixtures were subjected to simple cooling from a high-temperature liquid to a low-temperature solid phase. However, an α-melt-mediated transformation into β′ and β 2 resulted in the formation of immiscible phases in concentration ranges of SLS below 30%. By contrast, at SLS concentration ranges above 30%, the α-meltmediated transformation caused crystallization of only the γ form, and β′ and β 2 crystals did not appear. These results show that the specific interactions between SOS and SLS are operative in the phase behavior of the mixture states of SOS and SLS.The phase behavior of TAG mixtures is one of the major factors that determines the macroscopic properties of fat products, such as mouthfeel, appearance, and rheology, together with fat polymorphism, crystal size, morphology, and crystal network formation (1-8).Real fat systems of both vegetable and animal origin are multicomponent systems containing different kinds of FA moieties. The complex features of real fat systems are due to fat polymorphism as well as the mixing behavior of different TAG. The physical analysis of real fat systems usually starts with understanding the individual TAG molecules and subsequently moves on to understanding the mixed systems. The best approach for the latter task usually starts with studying binary mixture systems of different TAG and extends to ternary and multicomponent mixture systems. Therefore, many studies of binary phase behavior have been performed for different combinations of TAG mixtures (9-15).In the phase behavior of binary mixture systems, three typical phases can occur: a solid-solution phase, a eutectic phase, and molecular compound formation. The general tendency in the relationship between molecular interactions and phase behavior may be summarized as follows: (i) The two components (A and B) can exchange places with one another in the crystal lattice in all concentration ratios (solid-solution phase); (ii) no solubilities will exist in the lattices of crystals A and B, respectively (eutectic phase); and (iii) highly specific interactions can give rise to the formation of molecular compounds. In the particular case of the mixture of tristearin/tripalmitin (SSS/PPP) (16,17), metastable α and β′ forms were shown to exhibit continuous solid solutions, yet a eutectic nature was revealed in the most stable β form. For PPP/1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) mixtures (18,19), eutectic phases were observed in the metastable α and β′ forms and in the most stable β form as well. Recent studies on phase behavior have revealed various types of binary mixtures of TAG that form molecular compounds: 1,3-distearoyl-2-oleoyl-sn...

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

“…The transient metastable states are restricted to pure TAGs containing both saturated and unsaturated acyl chains (Kodali et al, 1987;Takeuchi et al, 2000;Ueno et al, 1997) or mixtures thereof (Takeuchi et al, 2002) including natural fats such as lard or cocoa butter (Loisel et al, 1998;Riiner, 1970). Thus, to understand polymorphic transformations taking place in TAGs, especially in natural fats, the structures of various unstable phases have to be determined.…”

Binary Phase Behavior of Saturated-Unsaturated Mixed-Acid Triacylglycerols—A Review

“…Ikeda et al analyzed the phase behavior of the binary mixtures of POP/OPO and POP/PPO, including a model solvent of n-dodecane. The β form of the MC was always observed in solutions 50 , 20 , even in a dilute solution including 2 POP OPO POP PPO and 98 ndodecane. These results indicate that specific molecular interactions must occur between POP and OPO and between POP and PPO molecules to create the MC crystals, even under the influence of solvent molecules 28,29 .…”

“…More experimental and modeling work is required to understand the mechanism. Binary phase behaviors of various saturated-unsaturated mixed-acid TAGs are summarized in Table 2 6, 9, 11 16,20,24,25,30 .…”

“…For simplicity, multiple β and β forms (β 2 , β 1 , β 2 , β 1 ) are represented by β and β. Polymorphic forms with double or triple chain-length structure are presented as α-2, γ-3, β -2. a P: palmitoyl, S: stearoyl, O: oleoyl, R: ricinoleoyl, L: linoleoyl, E: elaidoyl (data based on previous research) 1,[13][14][15][16][17][18][19][20][21][22][23][24][25] arate leaflets, with stabilized aliphatic chain-chain interactions. With regard to POP/OOP, in case 1, it causes destabilization due to the coexistence of oleoyl and palmitoyl chains in both the leaflets.…”

“…Takeuchi et al studied the binary mixture of SLS/SOS SLS: 1,3-distearoyl-2-linoleoyl-sn-glycerol 20 . As shown in Fig.…”