The quality of palm mid fractions (PMF) obtained by dry fractionation has increased, but the best-quality PMF for application in many confectionery fats are still produced by solvent fractionation. In the present study, liquid-liquid phase separation has been observed in acetone solutions both for pure triacylglycerols and for palm olein. The temperature at which phase separation occurs increases as the oil concentration is increased and linearly as the water content of the system is increased. The triacylglycerol compositions of the two liquid phases that form do not differ. However, the oil-rich phase is depleted with respect to the polar components. The temperature at which liquid-liquid phase separation occurs is reduced by about 0.2 and 0.4 7C per percent of free fatty acids and diacylglycerols, respectively. When oil-rich droplets appear, crystallisation occurs within them rather than in the oil-depleted phase, due to the higher oil concentration. Thus, liquid-liquid phase separation prior to crystallisation raises the nucleation temperature but may lead to a greater concentration of entrained olein in the filter cake, leading to a poorer-quality PMF.

The crystallization and recrystallization of fats have a significant impact on the properties and quality of many food products. While crystallization has been the subject of a number of studies using pure triacylglycerols (TAG), recrystallization in similarly pure systems is rarely studied. In this work, perdeuterated tripalmitoylglycerol ( (2)H-PPP) was dissolved in medium chain triacylglycerol oil (MCT) to yield a saturated solution. The solution was heated to cause partial melting of the solid and dissolution of the molten fraction of (2)H-PPP in MCT and was then cooled to the original temperature to induce recrystallization from the supersaturated solution. (2)H NMR was used to monitor the disappearance of (2)H-PPP from the solution and showed that recrystallization occurred in two steps. The first step was rapid, taking place over a few minutes, and accounted for more than two-thirds of the total recrystallization. The second step was much slower, taking place over a remarkably long timescale of hours to days. It is proposed that dissolution occurs from all parts of the crystals, leaving an etched and pitted surface. The first step of crystallization is the infilling of these pits, while the second step is the continued growth on the smoothed crystal faces.