Partitioning of triacylglycerols in the fractional crystallisation of palm oil

Palm oil is industrially fractionated on a large scale to yield a liquid olein (OL) product composed primarily of low melting triacylglycerols (TAGs) and a solid stearin (ST) product primarily of high melting TAGs. The physical and chemical properties of these fractionated products differ greatly from the original oil, and have added value. The aim of the work presented in this thesis is to study the partitioning of TAGs during the fractional crystallisation of palm oil and how this relates to their theoretical thermodynamic driving forces for crystallisation. Palm oil was studied under isothermal, non-isothermal and postcrystallisation stepwise remelting conditions. Filtered OL and ST products from the experiments were analysed for their TAG compositions by High Performance Liquid Chromatography (HPLC). Raw composition results showed fully saturated TAGs partitioning significantly to the ST phase, but little difference was observed in the compositions of the more unsaturated TAGs between the OL and ST (it would be expected that these would naturally concentrate in the OL). These observations are attributed to high levels of entrained liquid in the filter retentate, which has also been previously reported in the literature. A correction method based on the assumption that no triunsaturated TAGs should be able to crystallise to any significant extent was proposed to recalculate "true" ST compositions. These calculations indicated very high levels of entrainment (with the retentate possessing more liquid than solid), with typically only about 10% of palm oil TAGs crystallising despite forming a thick slurry. Although this assumption has not been directly verified, the corrected compositions showed behaviour that was very consistent with that which would be expected from thermodynamic driving force considerations. In the isothermal and non-isothermal studies conducted, the corrected ST composition revealed that PPP and other saturated TAGs showed the fastest transformation into the ST phase, followed by POP and other monounsaturated TAGs which predominated only once the saturated TAGs had been depleted from the OL phase. Slightly higher concentrations of PPP were achieved at higher isothermal temperatures (in isothermal studies) and lower cooling rates (in non-isothermal studies). Remelting studies on palm oil revealed that the melting process was largely dominated by trisaturated TAGs. This work has also demonstrated that the Focused Beam Reflectance Measurement (FBRM) technique was capable of detecting particle size and population numbers within the crystallising palm oil system and is a useful probe for detecting multiple events occuring in the crystalliser such as nucleation, melting, agglomeration and deagglomeration.