Revealing the influence of tempering on polymorphism and crystal arrangement in semicrystalline oil-in-water emulsions

The influence of tempering (i.e., successive heating and cooling) on crystallization properties of semicrystalline milk fat-in-water emulsions was studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and cryoscanning electron microscopy. Melting profiles obtained by DSC indicate a fractionation process of milk fat in every individual fat droplet. The long spacings, as observed by XRD, were useful in the designation of polymorphic changes to a shift in fatty acid composition of the crystals. An increased layer thickness of the 3L-crystals at 20 and 30 degrees C tempering points to a preferential incorporation of long-chain unsaturated fatty acids over short-chain fatty acids. Additionally, at 30 degrees C, an increased layer thickness of the 2L-crystals assumes the incorporation of longer-chain saturated fatty acids. The highly mixed crystals, an inherent property of milk fat, seem to be fractionated in purer crystals grouping triacylglycerols with a similar fatty acid composition. Moreover, a A different crystal organization was obtained for both tempering temperatures, where tempering at 20 degrees C appears to result in a coarser structure with well-defined lamellar regions near the interface, while tempering at 30 degrees C seems to lead to a finer, more homogeneous crystal structure. The observed effects on the microstructural level will have implications on storage stability and applicability