Epitaxial Growth of Fat Crystals on Emulsifier Crystals with Different Fatty Acid Moieties

Abstract

We performed in situ observations of the crystallization and melting behaviors of palm mid fraction (PMF) on sorbitan ester (SE) crystals comprising different fatty acid moieties (sorbitan tripalmitate (STP), sorbitan tristearate (STS), or sorbitan tribehenate (STB)) to reveal the epitaxial relationship between fat crystals and emulsifier crystals. The effects of SEs on the thermal behavior and polymorphism of PMF were investigated by differential scanning calorimetry and synchrotron radiation X-ray diffraction. These measurements showed that the addition of STP and STS greatly increased the crystallization temperature of PMF, which was caused by the crystallized SEs that were nucleated prior to PMF. Microscopic observations demonstrated that PMF crystals were oriented in the same direction as crystals of STP and STS because the chain lengths of the fatty acid moieties were similar to those of PMF. In contrast, when STB was used as a substrate, PMF crystals were not oriented in the same direction as STB crystals because there is a large difference between the chain lengths of STB and PMF. These results revealed that crystal growth of PMF on STP and STS crystals occurs via epitaxial growth, whereas PMF crystallization on STB crystals occurs via general heterogeneous nucleation.