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Ultra Small Angle X-Ray Scattering Studies of Triacylglycerol Crystal Networks

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Title: Ultra Small Angle X-Ray Scattering Studies of Triacylglycerol Crystal Networks
Author: Peyronel, M. Fernanda
Department: Department of Food Science
Program: Food Science
Advisor: Dr. Marangoni, AlejandroDr. Pink, David
Abstract: This thesis is an investigation into the use of ultra small angle x-ray scattering, USAXS, to study triacylglyerol (TAG) crystal networks. USAXS is an in-situ technique that requires no manipulation of the native material and allows the characterization of structures from about 10 nanometers to about 10 micrometers. A Bonse-Hart instrument at the Advanced Photon Source (APS) in Argonne National Laboratory was used to measure the scattering intensity, I(q), as a function of wave vector, q, in the region from 4 x 10-4 Å-1 to 0.1 Å-1. Plots of log[I(q)] vs log[q] were analysed using the Unified Fit and the Guinier-Porod models. Model binary TAG systems such as tristearin (SSS) and tripalmitin (PPP) solids in liquid triolein (OOO) were studied, followed by studies of pure solid single TAGs: SSS and PPP. This was followed by studies of three different complex systems and some commercial fats. The sizes and shapes of the scatterers and the aggregation structures formed from them were obtained from the fitting parameters. The interpretation of the results was aided by modelling and computer simulations carried out by colleagues. Up to four different structural levels were identified using the Unified Fit model for systems containing less than 20% solids. Crystalline nanoplatelets aggregated to form either cylinders, called TAGwoods, or a structure intermediate between a nanoplatelet and a TAGwood. Furthermore, the aggregation of TAGwoods gave rise to fractal structures brought about by diffusion or reaction limited cluster-cluster aggregation. The last structural level observed was identified as either evenly distributed clusters of TAGwoods or as a diffuse surface. Systems containing more than 50% solids showed nanovoids (empty holes in pure solid materials) or nano-spaces (oil filled cavities). The fractal nature of the walls of those cavities was characterized. USAXS has been shown to be a useful technique in identifying and quantified the hierarchies of the solid fats networks in edible oils and has identified a mechanism by which the structural levels appeared. This information should help the fat industry in their quest for finding healthy fat-replacers by identifying the existing structures that should be maintained.
Date: 2014-12
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