Interactive Polymorphic Crystallization Behavior in Eutectic Triacylglycerol Mixtures Containing Molecular Compound Crystals
Shinichi Yoshikawa, Shimpei Watanabe, Yoshinori Yamamoto, Fumitoshi Kaneko, Kiyotaka Sato
Abstract
Polymorphic crystallization behavior in mixture systems of three triacylglycerols (1,3-distearoyl-2-oleoyl-sn-glycerol (SOS), 1,3-dioleoyl-2-stearoyl-sn-glycerol (OSO), and trilauroylglycerol (LLL)) was examined via differential scanning calorimetry (DSC), synchrotron radiation X-ray diffractometry (SR-XRD), and polarized optical microscopy (POM). These three triacylglycerols are widely employed in confections, cosmetics, and other applications. They exhibited immiscible eutectic behavior, in which SOS and OSO formed molecular compound (MCSOS/OSO) crystals with a 1:1 compositional ratio. In each mixture system, the polymorphic form of LLL crystallizing during cooling switched from metastable β′ to stable β soon after crystallization of MCSOS/OSO in the β form. This behavior contrasts strongly with that of a pure system, in which LLL preferentially crystallizes in the β′ form, not directly in the β form. Strong interactions between LLL and MCSOS/OSO may dominate the polymorphic crystallization of LLL even if LLL and MCSOS/OSO do not form a miscible mixture. The present study provides new preparation concepts for novel types of functional fats impervious to structural deterioration during polymorphic transformations from metastable to stable forms.