39D-2

J. A. GALLEGOS-INFANTE, Departamento de Investigacion y Posgrado en Alimentos, Universidad Autonoma de Queretaro, Centro Universitario Cerro de las Campanas, Facultad de Quimica, Queretaro, 76010, Mexico, R. Rico-Martinez, Departamento de Ingenieria Quimica, Instituto Tecnologico de Celaya, Blvd. Garcia Cubas esq. Tecnologico, Celaya, Mexico, and J. D. J. Zazueta.

The lipid crystallization is very common in industrial operations and in biological functions. There is a lack of knowledge about the lipid crystallization, from the point of view. We used two different model systems (with pures triacylglicerides and a complex blend, olive oil). Tripalmitin - triolein and tripalmitin - olive oil in concentrations up to 0.5 in mole fraction of tripalmitin and a DSC for experimental data of global crystal growth rate, four diferent crystallization temperatures were used in each case (in isothermal form), held 60 min in each temperature, the blends were heating to eliminate thermic memory (80°C for 30 min) the cooling rate in DSC scan was 10°C/min. A traditional model of kinetics of phase transitions, the Avrami model was used. It shows serious problems in reproducing the dynamic behavior observed in the systems. Observing that the diffusion plays an important role in the process of solid formation we resort to use of the D-model, this model has not been used in lipids. The D-model was succesfull in modelling the observed behavior if the levels of supercooling were not too high. The presence on non-integer Avrami indexes suggest the presence of clusters before the start of the crystallization process. This fact and the problems of transport phenomena are the origin of the lack of success of the Avrami model in modelling the kinetics of phase transitions. The nucleation parameters obtained with the use of expressions of classic theory of nucleation showed that the pure triglycerides shown an anomalous behavior in these parameters, which was not present in the case of olive oil. Thus the use of classical model system tripalmitin - triolein is not good for reproduce the behavior in the real lipid blends when the system has high concentrations of tripalmitin.