Synchrotron Radiation Microbeam X-ray Analysis of Fat Crystal Nucleation on Emulsifier Crystals

We used synchrotron radiation microbeam X-ray diffraction (SR-mu-XRD) analysis to examine the effect of emulsifier crystal orientation and lattice periodicity on fat crystallization. Palm mid-fraction (PMF) and sorbitan esters (i.e., sorbitan tristearate (STS) and sorbitan tribehenate (STB)) were used as the fat and emulsifiers, respectively. The major findings were as follows. Diffraction patterns for the PMF crystal-mixed STS showed that the orientation of the lamellar planes of STS crystals and PMF a forms was similar. However, the orientation of some of the lamellar planes between STB crystals and PMF a forms was different in the PMF crystal-mixed STB. The findings showed that crystallization of PMF on STS crystals occurs via epitaxial growth, whereas PMF crystallization on STB crystals occurs via heterogeneous nucleation. Further, the findings suggest that the nucleation mechanism for the PMF a form was dependent on similarities between the molecular structure of the PMF a form and STS or STB, and that these similarities influenced the crystallization temperature for the PMF a form. The crystallization of PMF mixed with STB that occurred via heterogeneous nucleation therefore appeared to be affected by the differences in chain length between the PMF a form and STB, as well as steric hindrance of STB molecular structure including the hydrophilic group.