Fat Crystallization in Emulsion:  Influence of Emulsifier Concentration on Triacylglycerol Crystal Growth and Polymorphism

Crystallization of triacylglycerols (TAGs) is studied in emulsion by time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) coupled with DSC on a single sample consisting of an emulsion of palm oil dispersed in water. This oil-in-water emulsion (20% palm oil), stabilized by food grade sodium caseinate and by propylene glycol monostearate (PGMS), a food emulsifier, is used as a model for the study of the influence of emulsifiers on both TAG polymorphism and nucleation. Thermal and structural evolutions of this TAG mixture are monitored by a XRDT/DSC technique within the droplets during its crystallization and subsequent melting. In the specific conditions used and thanks to the high flux of synchrotron light, we demonstrate that both crystallization and polymorphism of a fat mixture are influenced by the presence of PGMS. The technique is sensitive enough to detect variations induced by the presence of emulsifier amounts ranging between 0 and 0.2%. Despite the low amount added, the presence of PGMS induces large changes in the crystallization temperature (about 2 °C) and energy (about 20%) as well as in structural evolutions, which were interpreted as a direct interference on specific TAG crystallization. Polarized light microscopy as a function of temperature and SAXS of oil−water−emulsifier mixture confirmed that the crystallization of emulsifier in the oil compartment is responsible for the changes of polymorphism and phase transitions observed via an indirect process. PGMS solubilized in sunflower oil with excess water shows self-organization in the oil phase with a lamellar period of 52.7 Å below 19 °C.