Kinetic Study on Alpha-Form Crystallization of Mixed-Acid Triacylglycerols POP, PPO, and Their Mixture.

Abstract

The crystallization behavior of the metastable form of triacylglycerols (TAGs) plays a critical role as a precursor for the crystallization of more stable and forms for various applications in food and pharmaceutical products. However, precise analysis of the crystallization kinetics of has not been performed, likely due to its rapid and complex behavior. This paper presents the observation results of the initial stages of the isothermal crystallization kinetics of forms of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP), 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (rac-PPO), and molecular compound (MC) crystals of a POP/rac-PPO (1/1) mixture (MC) using synchrotron radiation time-resolved X-ray diffraction and polarized optical microscopy. In all the TAGs, crystals with a worm-like morphology started to grow rapidly in the first stage. Then, the crystals slowly transformed into more stable forms in different manners for different TAG samples. In POP, the conversion was simple, as the -2 form transformed into -3, whereas in rac-PPO, the lamellar distance values of the -2 form continuously decreased with time and changed into the -3 form. In the MC crystals, in contrast, separate crystallization of -2 of a rac-PPO fraction initially occurred, followed by the crystallization of -2 of POP, and the two forms merged into -2 of MC. This separate crystallization was caused by large differences in the crystallization kinetics of the forms of POP and rac-PPO.