Retardation Mechanism of Crystallization of Diacylglycerols Resulting from the Addition of Polyglycerol Fatty Acid Esters

Edible oils containing high concentrations (>80%) of diacylglycerols (DAG oil) have beneficial health effects on obesity and obesity-related diseases; however, at low temperature, undesired precipitation of high-melting fractions in DAG oil can occur. Thus, preventing the precipitation of high-melting saturated fatty acid moieties in DAG oil is crucial for its expanded use. In this study, we investigated the mechanism of retardation of crystallization of DAG oil through the addition of polyglycerol fatty acid esters (PGFEs). We observed the occurrence of birefringence under polarized crossed-Nicols conditions in the PGFE-added DAG oil. We also found that prior to the crystallization of high-melting DAG fractions, PGFE-added DAG oil showed shear-rate-dependent changes in viscosity, providing strong evidence for the existence of self-assembled structures that lead to the birefringence. Furthermore, small- and wide-angle X-ray diffraction patterns suggest the formation of a supramolecular assembly comprising DAGs and PGFEs, which is significantly different from the structure of DAG crystals. From these results, we conclude that the retardation of crystallization of DAG oil is caused by the formation of liquid-crystal-like supramolecular complex structures that contain high-melting fractions of DAGs and PGFEs. These complexes may disturb the formation of critical nuclei of high-melting DAG fractions during the prenucleation crystallization stage