Tripalmitin‐Driven Crystallization of Palm Oil: The Role of Shear and Dispersed Particles

Abstract

AbstractWhile palm oil (PO) is a reliable ingredient in formulations for biscuits, cream fillings, and compound chocolates, our understanding of its crystallization behavior and physico‐chemistry pales in comparison to many other fats and oils. Phase diagrams of triacylglycerol (TAG) mixtures may be used to elucidate fat crystal polymorphism and composition of such oils, yet conditions important to the food industry such as shear speed, relevant processing temperatures, and presence of secondary ingredients are regularly overlooked. Here, the effects of shear speed (n = 0–500 RPM), dispersion concentration (0–5 wt.%), and dispersed particle surface chemistry [silica or octadecyl‐functionalized (C18) silica] on the thermal properties of commercial PO when cooled from 60 to 20 °C at 1 °C min−1 were explored, with focus placed on PO's higher‐melting fraction. Using a series of high‐purity TAG standards, X‐ray diffraction revealed PO's higher‐melting fraction as mainly composed of tripalmitin (PPP) crystals and molecular compounds (MC) of PPP either with 1,3‐dipalmitoyl‐2‐oleoyl‐sn‐glycerol (POP) or with POP and 1,2‐dipalmitoyl‐3‐oleoyl‐rac‐glycerol (PPO) in combination, all in a double chain‐length β' (i.e., β'‐2) conformation. Shear increased the formation of lower‐melting α‐2 POP and β'‐2 MCPOP:PPO:PPP crystals while depleting the system of β'‐2 MCPOP:PPP and β'‐2 PPP crystals. This loss was further exacerbated by the addition of dispersed particles to the point where PPP was completely incorporated as MC and β'‐2 PPP crystals were eliminated. While heterogeneous nucleation tends to favor kinetic products of fat crystallization, the interactions between shear and surface chemistry varied between crystal types.