Relationships between molecular structure and kinetic and thermodynamic controls in lipid systems: Part III. Crystallization and phase behavior of 1-palmitoyl-2,3-stearoyl-sn-glycerol (PSS) and tristearoylglycerol (SSS) binary system

The phase behavior of 1-palmitoyl-2,3-distearoyl-sn-glycerol (PSS)/tristearoylglycerol (SSS) binary system was investigated in terms of polymorphism, crystallization and melting behavior, microstructure and solid fat content (SFC) using widely different constant cooling rates. Kinetic phase diagrams were experimentally determined from the DSC heating thermograms and analyzed using a thermodynamic model to account for non-ideality of mixing. The kinetic phase diagram presented a typical eutectic behavior with a eutectic point at the 0.5PSS mixture with a probable precipitation line from 0.5PSS to 1.0PSS, regardless of the rate at which the sample was cooled. The eutectic temperature decreased only slightly with increasing cooling rate. PSS has a strong effect on the physical properties of the PSS–SSS mixtures. In fact, the overall phase behavior of the PSS–SSS binary system was determined, for a very large part, by the asymmetrical TAG. Moreover, PSS is a key driver of the high stability observed in crystal growth, polymorphism and phase development. Levels as low as 10% PSS, when cooled slowly, and 30% when cooled rapidly, were found to be sufficient to suppress the effect of thermal processing.

► Binary phase diagram of PSS and SSS demonstrate a eutectic at 50% molar ratio. ► From molar ratios of 10%, PSS insulates the effects of kinetics on the phase transformation behavior of SSS. ► SSS/PSS kinetic phase diagram presented an apparent typical eutectic behavior with a eutectic concentration of 50% PSS.