Polymorphism and Kinetic Behavior of Binary Mixtures of Trisaturated Triacylglycerols Containing Palmitic and Stearic Acid Under Non-Isothermal Conditions

The kinetic phase behavior and phase transformation paths of pure tripalmitoylglycerol (PPP), 1-palmitoyl-2,3-distearoyl-sn-glycerol (PSS), and 1,3-dipalmitoyl-2-stearoyl-sn-glycerol (PSP) and binary mixtures thereof, are investigated at 10.0 degrees Cmin(-1) (fast cooling) and 1.0 degrees Cmin(-1) (slow cooling) cooling rates, and further re-heating at 5.0 and 1.0 degrees Cmin(-1). Mixtures are studied in terms of polymorphism, crystallization, and melting behavior. Kinetic phase diagrams are determined from DSC heating thermograms and XRD data. Independent of the cooling rate, most samples crystallized in the -polymorph and transformed into the more stable -form via melt-mediated crystallization or direct recrystallization from the -phase. Samples containing a high amount of PSP crystallized in the -form at slow cooling rate and samples containing high PPP concentration ultimately transform to the most stable -form. The kinetic phase diagram of PPP-PSS mixtures present an apparently typical eutectic behavior with a eutectic point at X-PSS=0.3, when the samples are melted at the higher heating rate, which shifts to higher concentration, X-PSS=0.5, when the lower heating rate is applied. The eutectic temperature (58.40.3 degrees C) is independent of the cooling and heating rates used. The kinetic phase diagram of PSS-PSP mixtures display two types of behaviors, a probable monotectic behavior in the most stable phase and a eutectic behavior in the meta-stable phase when the samples are melted at higher heating rate. This study shows that PSS has a strong effect on the physical properties of PPP-PSS blends and affects a large part of the phase behavior of this binary system. At lower PSS concentrations, the mixtures transform to the most stable form, but at increasing PSS concentration, the samples stabilize in the -phase. In the PSS-PSP binary systems, all the mixtures stabilize in the -phase, which is preferred in many food applications since it is associated with a smooth texture.Practical Applications: This research extends a previous study on the phase behavior of the most common trisaturated triacylglycerols and the results are useful for the food industry as they can help in understanding the functionality of hard fat based structuring agents in end applications, and in developing new triacylglycerol based crystallization and structuring agent for specific food applications.