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

• Published in: Molecules (Basel, Switzerland) Vol. 26; no. 1; p. 220
• Main Authors: Taguchi, Ken, Toda, Akihiko, Hondoh, Hironori, Ueno, Satoru, Sato, Kiyotaka
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 04.01.2021; MDPI
• Subjects: Crystallization; crystallization kinetics; Crystals; fat; Food production; Glycerol; Kinetics; Light microscopy; Morphology; Nanoparticles; Optical microscopy; Phase Transition; polarized optical microscopy; polymorphism; Synchrotron radiation; Synchrotrons; Tags; Thermodynamics; Triglycerides; Triglycerides - chemistry; X-Ray Diffraction; X-ray diffraction; fat; polymorphism; crystallization kinetics; polarized optical microscopy
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules26010220

The crystallization behavior of the metastable α form of triacylglycerols (TAGs) plays a critical role as a precursor for the crystallization of more stable β' and β forms for various applications in food and pharmaceutical products. However, precise analysis of the crystallization kinetics of α 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 α forms of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP), 1,2-dipalmitoyl-3-oleoyl- -glycerol ( -PPO), and molecular compound (MC) crystals of a POP/ -PPO (1/1) mixture (MCPOP/PPO) using synchrotron radiation time-resolved X-ray diffraction and polarized optical microscopy. In all the TAGs, α crystals with a worm-like morphology started to grow rapidly in the first stage. Then, the α crystals slowly transformed into more stable forms in different manners for different TAG samples. In POP, the conversion was simple, as the α-2 form transformed into γ-3, whereas in -PPO, the lamellar distance values of the α-2 form continuously decreased with time and changed into the α-3 form. In the MCPOP/PPO crystals, in contrast, separate crystallization of α-2 of a -PPO fraction initially occurred, followed by the crystallization of α-2 of POP, and the two α forms merged into α-2 of MCPOP/PPO. This separate crystallization was caused by large differences in the crystallization kinetics of the α forms of POP and -PPO.