Phase behavior of binary mixtures of three different 1,3‐diacylglycerols

Abstract

Compared to triacylglycerol compositions, 1,3‐diacylglycerols (1,3‐DAG) have gained far less concern. Consequently, studying the mixing behavior of representative 1,3‐DAG components in palm‐based DAG oils such as 1,3‐dipalmitoyl‐sn‐glycerol (1,3‐PP), 1‐palmitoyl‐3‐oleoyl‐sn‐glycerol (1,3‐PO), and 1,3‐dioleoyl‐sn‐glycerol (1,3‐OO) is of critical interest. This study focused on the phase behavior of binary mixtures for 1,3‐PO/1,3‐OO, 1,3‐PP/1,3‐OO, and 1,3‐PO/1,3‐PP through polarized light microscopy (PLM) and differential scanning calorimetry (DSC) at 1 and 10°C/min cooling and melting rates. The kinetic phase diagrams of 1,3‐PO/1,3‐OO, 1,3‐PP/1,3‐OO, and 1,3‐PO/1,3‐PP constructed using melting DSC thermograms indicated that obvious eutectic behaviors were detected for 1,3‐PO/1,3‐OO and 1,3‐PO/1,3‐PP with eutectic composition at 0.2 × 1,3‐PO and 0.1 × 1,3‐PP, respectively, while 1,3‐PP/1,3‐OO showed an monotectic behavior. The simulation of the liquidus boundaries for two eutectic binary systems of 1,3‐PO/1,3‐OO and 1,3‐PO/1,3‐PP produced negative ρ values for all their segments apart from the region of 0 ≤ X1,3‐PP ≤ Xe at both cooling rates, which indicated that the molecular interactions between 1,3‐PO and 1,3‐OO or 1,3‐PO and 1,3‐PP in region of Xe ≤ X1,3‐PP ≤ 1 were inclined to favor the formation of mixed‐pairs. The PLM results exhibited that the variations in the microstructure were strongly affected by the adding components, especially apparent at compositions in proximity of the eutectic composition.Practical application: Palm‐based DAG oils have attracted much interest because of the unique properties. 1‐palmitoyl‐3‐oleoyl‐sn‐glycerol, 1,3‐dipalmitoyl‐sn‐glycerol, and 1,3‐dioleoyl‐sn‐glycerol are representative 1,3‐DAG components in palm‐based DAG oils. The study of the phase behaviors of these representative 1,3‐diacylglycerols will contribute to exploring the fractionation, phase development and crystallization of palm‐based DAG oils, which makes DAG oils even more interesting as functional oils with distinct physicochemical characteristics and nutritional advantages.DSC melting profiles of 1,3‐PO/1,3‐OO binary mixtures obtained at (a) 10°C/min and (b) 1°C/min heating rate and the corresponding binary phase diagrams. The result exhibits that the differing rates have an influence on the melting thermograms including the peak shapes, melting onset, and offset. Nevertheless, these differences are not to the degree of altering the sequence of phase transition of 1,3‐PO/1,3‐OO binary mixtures.