Viscosity and its relationship to crystallization in a binary system of saturated triacylglycerides and sesame seed oil
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This paper describes the relationship of viscosity with the crystallization process in a binary system formed by sesame oil and different concentrations of tripalmitin (TP) and tristearin (TS) (0.0, 0.032, 0.098, 0.18, 0.26, 0.344 g/dL). The behavior of the reduced viscosity (ηred) indicated that TP and TS affected the native bilayer lamellar organization of sesame oil triacylglycerides. The behavior of ηred at TP or TS concentrations ≤0.098 g/dL suggested that, as a result of intermolecular interactions between the saturated triacylglyceride and the unsaturated triacylglycerides of sesame oil, the oil solution developed lamellar structures with a smaller size than the native structures in sesame oil. At TP or TS concentrations >0.098 g/dL, the behavior of ηred indicated that TP or TS segregated out of the lamellar structure as the temperature was decreased. The kinetics of the segregation phenomenon was a function of the concentration of saturated triacylglyceride and the type of triacylglyceride (i.e., TP or TS), and was favored by an increase in the shear rate. In all situations, the temperature of nucleation was achieved when ηred = 0, which may represent the point at which the interfacial energy between sesame oil and the developing nuclei achieved its maximum value. The higher the intermolecular interaction between the TP or TS and the triacylglyceride structure of the sesame oil, the lower the temperature at which ηred = 0 in the oil solutions. As a result, the diffusion term (i.e., viscosity of the liquid phase) became a limiting factor for crystal growth rate, especially at TP and TS concentrations ≤0.18 g/dL.
