Crystallization behavior of low molecular weight milk fat fractions

Milk fat was fractionated with supercritical CO2 at 100 bar and 40oC to produce low molecular weight fractions (LMWF1 and LMWF2). The fractions were continuously collected every 2 h and evaluated for FA composition, isothermal crystallization using pNMR, DSC, XRD and rheometer. Short chain, medium chain and total saturated FAs decreased with each successive fraction obtained with time at 100 bar, whereas long chain and total unsaturated FAs increased. Multi-step behavior was observed from isothermal crystallization curves obtained from pNMR at any selected temperatures across LMWFs and MF except at 11oC and 12oC in LMWF1, 15oC in LMWF2 and at 25oC in MF. According to the isothermal DSC curves of LMWFs at various temperatures it was observed that as temperature increased, the nucleation time and the time of maximum crystallization rate of LMWF1 and LMWF2 appeared later. While from the melting thermograms of LMWFs, the peaks appeared at higher temperatures as isothermal crystallization temperatures increased. XRD results indicated that the differences in FA compositions of LMWFs studied did not affect the formation of crystal polymorphs, but only caused differences in induction times. Shear increases the crystallization and reduces the crystallization nucleation and growth time below a critical shear rate.