Effect of processing conditions on crystallization kinetics of a milk fat model system

Crystallization behavior of three blends of 30, 40, and 50% of high-melting fraction (MDP = 47.5 degreesC) in low-melting fraction (MDP = 16.5 degrees C) of milk fat was studied under dynamic conditions in laboratory scale. Th e effect of cooling and agitation rates, crystallization temperature, and c hemical composition of the blends on the morphology, crystal size distribut ion, crystal thermal behavior, polymorphism, and crystalline chemical compo sition was investigated by light microscopy, differential scanning calorime try (DSC), X-ray diffraction (XRD) and gas chromatography (GC). Different n ucleation and growth behavior were found for different cooling rates. At sl ow cooling rate, larger crystals were formed, whereas at fast cooling rate, smaller crystals appeared together. Slowly crystallized samples had a broa der distribution of crystal size. Crystallization temperatures had a simila r effect as cooling rate. At higher crystallization temperatures, larger cr ystals and a broader crystal size distribution were found. Agitation rate h ad a marked effect on crystal size. Higher agitation rates lead to smaller crystal size. Cooling rate was the most influential parameter in crystal th ermal behavior and composition. Slowly crystallized samples showed a broade r melting diagram and an enrichment of long-chain triacylglycerols. Crystal lization behavior was more related to processing conditions than to chemica l composition of blends.