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

The crystallization behavior of the metastable [Formula: see text] form of triacylglycerols (TAGs) plays a critical role as a precursor for the crystallization of more stable [Formula: see text] and [Formula: see text] forms for various applications in food and pharmaceutical products. However, precise analysis of the crystallization kinetics of [Formula: see text] 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 [Formula: see text] 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 [Formula: see text]) using synchrotron radiation time-resolved X-ray diffraction and polarized optical microscopy. In all the TAGs, [Formula: see text] crystals with a worm-like morphology started to grow rapidly in the first stage. Then, the [Formula: see text] crystals slowly transformed into more stable forms in different manners for different TAG samples. In POP, the conversion was simple, as the [Formula: see text]-2 form transformed into [Formula: see text]-3, whereas in rac-PPO, the lamellar distance values of the [Formula: see text]-2 form continuously decreased with time and changed into the [Formula: see text]-3 form. In the MC [Formula: see text] crystals, in contrast, separate crystallization of [Formula: see text]-2 of a rac-PPO fraction initially occurred, followed by the crystallization of [Formula: see text]-2 of POP, and the two [Formula: see text] forms merged into [Formula: see text]-2 of MC [Formula: see text]. This separate crystallization was caused by large differences in the crystallization kinetics of the [Formula: see text] forms of POP and rac-PPO.