Measurement of shape and size of fat crystals by electron microscopy

The morphology of fat crystals plays an important role in the final properties of fat products, such as margarines, butter and shortenings. Product attributes such as spreadability, hardness and work softening are determined at least partly by the shape and size of the individual fat crystals and the way in which these crystals interact to form clusters, agglomerates and networks. Proper analysis of the morphology by electron microscopy is hampered by the presence of oil between the fat crystals. Two methodologies to remove the attached oil were compared. In the classical method, a suspension of fat crystals is made by treating the sample with a detergent solution to remove the oil. In a new approach, fat crystals, after removal of oil are fixed to a carbon film Two model fat crystal dispersions with small and large crystals obtained by cooling a fat blend to 5 degrees C and 35 degrees C, respectively, were analysed. Crystal size and shape were measured by a semi-automatic image analysis procedure. Both methods give reliable results for the determination of fat crystal habit. The new methodology, applying the fixation of fat crystals to a carbon film, is less elaborate and allows a better separation of fat crystals and fat crystal clusters.