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We investigated the crystallization behavior of coconut oil (CO) with tripalmitin (PPP) and tristearin (StStSt) as additives. The effects of cooling rates (2°C, 5°C, and 10°C min−1) and triacylglycerol concentrations (0.3–10 wt.%) on crystallization and melting behavior of CO were studied using differential scanning calorimetry (DSC) and optical microscopy. The polymorph was also examined using synchrotron radiation X‐ray diffraction (SR‐XRD). From the DSC results, two exothermic peaks for CO crystallization indicated two compositions in CO. From the SR‐XRD results, the α form crystallized first at a high crystallization temperature (HTc) followed by β′ crystallization at low temperature (LTc), after which both HTc‐α and LTc‐β′ transformed into the β′ form of CO (CO‐β′) solid solution during heating. Although the addition of PPP increased crystallization temperature of CO, it did not change its polymorphic pattern. However, during slow cooling with the StStSt additive, CO‐β′ crystallization was induced from the melt directly. Moreover, under isothermal conditions, the crystallized StStSt spherulites induced nucleation of CO more than did PPP. Therefore, PPP increased the crystallization temperature of CO in both HTc and LTc fractions without changing the polymorph of CO, while StStSt promoted crystallization of CO directly into CO‐β′.

This study evaluates the influence of the polymorphs of triacylglycerol (TAGs) seed crystals on the crystallization of coconut oil (CO) using seeding techniques. Tripalmitin (PPP) and tristearin (StStSt) with three polymorphs (α, β′, and βα forms) were used as the seed materials. β form seed crystals were prepared by transforming in the solid state from the α form (βα) and by annealing TAG powder (βann). The CO crystallization on the TAG seed crystals was observed at 20 °C using differential interference contrast microscopy and synchrotron radiation X-ray diffraction. The seed crystals with different polymorphs of PPP and StStSt promoted the nucleation of the β′ form of CO by heterogeneous nucleation. The seed crystals with the β′ form were the most effective accelerators, indicating that polymorphic matching between seed crystals and CO strongly induced the nucleation of CO by epitaxial growth. A longer TAG fraction (such as LMP, PPP, etc., L is lauric acid, M is myristic acid) of CO probably grew on the surface of the βann seed via the template effect with the same orientation as the seed. These results indicate that the seed crystal polymorphs significantly affect the efficiency of CO crystallization. Efficient seedings can be used to improve the physical properties of CO via fractionation.

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Hard fat stocks containing highly saturated fats are a necessary ingredient for fabrication of trans-free plastic fats. Crystal fractions obtained from the fractionation of fats naturally containing saturated fatty acids (SFA) may be a promising approach to produce the desired hard fat stocks. Influences of cooling rate (0.4, 2.0 and 10.0 CÁmin −1) and fractionation temperature (15 and 20 C) on the formation of solid fat crystals of rambutan (Nephelium lappaceum L.) kernel olein (RKOle) during acetone fractionation were examined using in situ observation with polarized light microscopy (PLM). The resulting stable crystals were then separated and characterized by their iodine values, fatty acid compositions, crystal polymorphism, solid fat index, and melting behavior. PLM results showed that cooling rate affected crystal formation. Entrained oil on the surface and number of small crystals increased at higher cooling rates of RKOle. Stable crystals were obtained at a cooling rate of 2.0 CÁmin −1 and 6 hours, which had lower iodine value and contained more SFA with a higher amount of solid fat than incipient RKOle. Crystals fractionated at 20 C were larger in size, fewer in number, and had less entrained oil compared to those fractionated at 15 C. Their main polymorph was the β' form with a melting range comparable to common fully hydrogenated oils. Results suggested that RKOle crystals have potential for use as hard fat stocks for various purposes.