Nuclear Magnetic Resonance (NMR) study of Palm Kernel Stearin: Effects of cooling rate on crystallization behaviour

In this study, effects of different cooling rates (0.5,3.3,4.7 and 6.9 °C/min) on the crystallization behavior of palm-kernel-stearin (PKS) were studied by low-field NMR relaxometry. According to results, solid fat content (SFC), longitudinal relaxation time (T₁), second moment (M₂) and degree of crystallinity (%) of the samples increased with increase in cooling rate from 0.5 to 6.9 °C/min. In contrast, transverse relaxation time (T₂) demonstrated an opposite behavior with respect to T₁ and decreased when the cooling rate increased. Additionally, effects of cooling rate on the changes of polymorph structures were detected by X-ray measurements. Degree of crystallinity showed high Pearson correlation values (α ≤ 0.05) with SFC (r = 0.771) and T₁(r = 0.932). Changes in the crystal polymorphs could also be explained by NMR parameters to some extent as can be observed by the strong correlation between the β crystal content and T₂ (r = 0.927). At the highest cooling rate, β′ crystals were the dominant polymorphic form and constituted 75(%) of the total crystals present. Results of this study suggested that NMR relaxometry could be used as a complementary tool to interpret the crystallization behavior of PKS.