Abstract
A model system with a heterogenous composition of triacylglycerides (TG), in which the component with the highest melting temperature crystallized independently, was developed. Thus, tripalmitin solutions in sesame seed oil (0.98, 1.80 and 2.62% w/v) with ideal crystallization behavior, evaluated through differential scanning calorimetry and the Hildebrand equation, were utilized as a model system to investigate the effect of supercooling and viscosity (η) on the development of polymorph states of TG crystals, their crystal growth mechanism, crystal growth rate constant (z), and activation energy associated with the crystallization process (E a). Results indicated that a modification of the Avrami equation, as suggested by Khanna and Taylor, provides reliable values of z and, subsequently, correct estimates of E a. This was not the case when the original Avrami equation was used. Subse quent analysis indicated that nucleation and crystal growth, as well as the polymorph states devel oped by the TG, depend mainly on η and the extent of supercooling. The latter is a function of the concentration of the TG with the highest melting temperature in the system (e.g. tripalmitin). In conclusion, it is feasible to model the combined effect of supercooling, the viscosity of the liquid phase, and the concentration of the component to crystallize, through multiple variable regression to predict the size, number and polymorph state of the crystals developed during the industrial process of fractional crystallization of vegetable oils and fats. This would allow us to establish process condi tions where a higher yield and separation efficiency of the crystal fraction could be achieved.
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