Image analysis of palm oil crystallisation as observed by hot stage microscopy

An image processing algorithm previously used to analyse the crystallisation of a pure fat (tripalmitin) has been applied to the crystallisation of a multicomponent natural fat (palm oil). In contrast to tripalmitin, which produced circular crystals with a constant growth rate, palm oil produced speckled crystals caused by the inclusion of entrapped liquid, and growth rates gradually decreased with time. This can be explained by the depletion of crystallisable material in the liquid phase, whereas direct impingement of crystals (the basis of the Avrami equation) was less common. A theoretical analysis combining this depletion with assuming that the growth rate is proportional to the supersaturation of a crystallisable pseudo-component predicted a tanh function variation of radius with time. This was generally able to provide good fits to the growth curves. It was found that growth rate was a relatively mild function of temperature but also varied from crystal to crystal and even between different sides of the same crystal, which may be due to variations in composition within the liquid phase. Nucleation rates were confirmed to vary approximately exponentially with decreasing temperature, resulting in much greater numbers of crystals and a smaller final average crystal size at lower temperatures

Characterisation of high 1,3-distearoyl-2-oleoyl-sn-glycerol content stearins produced by acidolysis of high oleic sunflower oil with stearic and palmitic acids

Nine different stearin fractions with 1,3-distearoyl-2-oleoyl-sn-glycerol (StOSt) contents ranging from 69–84% were obtained via fractionation from fats produced by acidolysis of high oleic sunflower oil (HOSO) with various mixtures of stearic (either 95 or 98% pure) and palmitic acids (98% pure). Samples were further treated with silica to reduce the oxidised glyceride and DAG content. Isothermal crystallisation at 20°C showed a single main peak, but evidence of crystallisation during the initial DSC transient was also apparent for high StOSt content samples. This was confirmed as the α form by stop-and-return DSC and XRD. The main crystallisation event was generally faster (including a shorter induction time) for samples with higher StOSt levels (lower POSt levels). Silica treatment generally accelerated transformations to higher polymorphs (γ, β′ and β). Raman microscopy experiments showed that crystallisation of the β-form was achieved after 7 days storage at 20°C but only in the silica treated stearin samples. This is consistent with higher solid fat content (SFC) values that were obtained with silica treated samples, which also increased with higher levels of StOSt. The results suggest that such stearins could potentially replace shea stearin in cocoa butter equivalents (CBE) formulations

Crystallization and polymorphism of cocoa butter equivalents from blends of palm mid fraction and hard stearins produced by enzymatic acidolysis of high oleic sunflower oil

Cocoa butter equivalents (CBEs) are formulated by mixing palm mid fraction (PMF) with silica-treated hard stearin fractions produced via enzymatic acidolysis of high oleic sunflower oil with various mixtures of stearic and palmitic acids. The CBE blends always contain ≈30% 1,3-distearoyl-2-oleoyl-sn-glycerol, but vary in 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP; 40–45%) and rac-1-palmitoyl-2-oleoyl-3-stearoyl glycerol (POSt; 10-16%) content. Overall symmetric disaturated monounsaturated (Sat-O-Sat) levels range from 81–86%. The effects of varying POP/POSt content on the non-isothermal and isothermal crystallization (at 20 °C) of the CBEs are then studied using differential scanning calorimetry (DSC), stop and return DSC, and X-ray diffraction (XRD), and compared with CB. Four polymorphs (I/sub-α, II/α, IV/β′, and V/β) are identified which appear at different stages. The addition of PMF (raising POP levels) slows crystallization rates compared to the original stearins, but higher levels of POP also produce a small amount of V/β in under 4 h at 20 °C via apparent transformation from II/α. This does not occur with (high POSt) CB samples. However, after storage at 20 °C for 7 days, CB demonstrates greater transformation to V/β (from IV/β′) as confirmed via XRD. Solid fat contents of CBE blends are higher than CB due to higher Sat-O-Sat levels. Practical applications: The paper demonstrates a new route for formulating CBEs. The relative proportions of StOSt, POSt and POP in the formulation can be controlled by changing the proportions of palmitic and stearic acid used in the enzymatic acidolysis and the blend ratio with the PMF. This can then be used to fine-tune the crystallization behavior