Comparative analysis of triacylglycerol composition, melting properties and polymorphic behavior of palm oil and fractions

Palm oil is without doubt the most widely fractionated oil. Dry fractionation is based on differences in the melting points of triacylglycerols (TAG) which will crystallize selectively during the cooling process. Unfortunately, limitations due to intersolubility, closely linked to polymorphism, induce formation of co-crystals at each crystallization step. For this reason, only restricted TAG enrichments are observed. In this work, a series of samples (24) of palm oil, solid and liquid fractions (stearins, mid fractions, oleins and superoleins) have been selected and examined in terms of TAG composition (by HPLC), differential scanning calorimetry (DSC) melting profile and variable temperature powder X-ray diffraction pattern. Three major endotherms [low-melting, high-melting and very high-melting peaks (LMP, HMP and VHMP)] are detected in the DSC melting profiles (5 degrees C/min). The VHMP is only recorded for palm stearin which contains more SSS components. The HMP contribution is weak for palm olein and even not observed for palm super oleins. The LMP is usually made up of UUU, SUU and SUS components; SUS components are observed in both LMP and HMP; the HMP is also made up of some SSS, except for palm oleins and super oleins. Sub-alpha(2), sub-alpha(1), alpha, beta'(2), beta'(1), and beta polymorphic forms are recorded; the LMP components preferentially crystallize in sub-alpha(2), sub-alpha, and alpha forms; the HMP components generally crystallize in beta'(2) and beta'(1), with a tendency to exhibit beta crystals, depending on the SSS content. Components of the VHMP have an increased tendency to stabilize in the 0 form; in view of the results, we can assume that there is a clear relationship between TAG composition, melting properties and polymorphic behavior and of palm oil and fractions.