Refined palm olein was dry fractionated via three different cooling programs on laboratory-scale fractionation equipment. The enrichment and depletion of the main triacylglycerols in the liquid and solid phase was plotted as a function of the crystallization degree of the oil. It was shown that for the given conditions and palm olein composition, the initial crystals mainly consisted of PPP, diacylglycerols, POP and PLP. At higher crystallization degrees, a sharp viscosity increase in the crystal suspension was primarily related to an obvious decrease of POP but also of POS in the recovered superolein, while the general crystallization rate of the system remained unchanged. Rather than a change in crystallization rate of POP, a change in the ratio between the crystallizing monounsaturated triacylglycerols is linked with the high viscosity of the crystal slurry. For a comparable degree of crystallization, the superolein of the more viscous crystal slurry, obtained through a membrane press filtration up to 15 bar, was more unsaturated than the superolein filtered from the less viscous slurry. Consequently, the high unsaturation in the corresponding soft palm mid fraction is only the result of an incomplete phase separation, and not due to an increased intersolubility of unsaturated triacylglycerols in the crystals.

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As are traditional fractionation technologies, static dry fractionation is a highly reliable technology for the consistent production of good-quality palm kernel stearin (PKS) for use as cocoa butter substitute (CBS) after total hydrogenation. A new process route now permits the production of unhardened yet high-quality CBS. Also an increase in total stearin yield can be achieved, via a successful refractionation of palm kernel olein. DSC analysis together with pilot static fractionation trials on the palm kernel olein indicates that a cooling water temperature that is too low (e.g., 17°C) may result in the quick formation of unstable crystals that are possibly later converted to a more stable form. The resulting mixture of crystals with a possibly different polymorphic structure is easily squeezed through the filter cloth during filtration, whereas a slower, but more homogeneous co-crystallization occurs at higher temperature (18°C or higher) and results in a much more stress-resistant slurry. Polarized light microscopy analysis confirmed that crystal size is not the only determining factor for a successful filtration. The total two-stage static fractionation of palm kernel oil (PKO) [iodine value (IV) 18] on a pilot scale results in the following three end products: PKS IV 5 (yield: 29%, for direct use as CBS), PK olein IV 27 (yield: 58%), and PKS IV 7 (yield: 13% for use as CBS after full hydrogenation). The unhardened PKS IV 5 has outstanding melting and crystallization properties, comparable to traditional hydrogenated stearin fractions. Therefore, rather than the higher stearin yield, the reduced hydrogenation capacity is most probably the most important benefit of the two-stage static fractionation process.Paper no. J11031 in JAOCS 82, 783-789 (November 2005).Owing to its high content of lauric and myristic acids, palm kernel oil (PKO) is well known as a suitable feedstock for the production of confectionery fats (1). For these applications the refined oil is commonly modified or blended. The highest-quality, steepest-melting fats resulting after modification are usually called cocoa butter substitutes (CBS) and are ideal to produce compound chocolate (2). These substitutes show physical properties similar to cocoa butter but differ considerably chemically. Hence, these fats have very little compatibility with cocoa butter (3). Besides cocoa butter-like physical behavior, high-quality CBS possess a good flavor release and show sufficient bloom resistance. Unlike cocoa butter, usually no tempering is needed during the production of confectionery (1,4). The modification from PKO to CBS is traditionally carried out via a combination of fractionation and hydrogenation. The former technology is still of great interest in the oil and fats industry. The basis of a fractionation is a fractional crystallization followed by a separation between the liquid olein fraction and the crystallized stearin fraction (5-7). Basically, there are three main strategies within this technology: dry fractionation, solvent fractiona...

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