Fractionation and characterisation of hard milk fat crystals using atomic force microscopy.

ABSTRACT

The hard milk fat (HMF) fraction of milk fat was isolated via dry, thermal fractionation, followed by a solvent washing process. The resulting HMF crystals were visibly free of entrapped liquid fat, and subsequently characterised by thermal analysis, X-ray diffraction, and electron microscopy. The HMF crystals were found to be mostly ß' and ß'2 crystalline structures, with a lamellar thickness of 42.7-44.1 Å. Additionally, crystal size was determined to be ≥1 µm in length and 0.4-1 µm in width. Atomic force microscopy (AFM) was used to further characterise the HMF crystals. AFM enabled 3D mapping and visualisation of crystal layering, as well as simple determination of layer thickness (∼4.2 ±â€¯0.8 nm); a value in close agreement with the results obtained via X-ray analysis. The AFM characterisation approach provides a simple method of characterising HMF crystals, without suffering the limitations of other widely used techniques.