Browsing by Author "Hill, Sandra"

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    Prediction of the Glass Transition Temperature on Extruded Waxy Maize and Rice Starches in Presence of Glycerol
    (Springer Nature, 2010) Enrione, Javier; Osorio, Fernando; Pedreschi Plasencia, Franco; Hill, Sandra
    Polymer science approach has shown to be useful to understand the structural complexity of food systems. This work looks at the effect of glycerol (5%, 10%, and 20% (dry weight basis)) on the glass transition temperature (Tg) of a starchy matrix determined by DSC and its prediction using Ten-Brinke-Karasz equation. Waxy maize starch (WMS) and rice starch (RS) systems were prepared by thermomechanical extrusion. A decrease in Tg, from similar to 170 to similar to 25 A degrees C, was detected for both starches (0% glycerol) when the moisture increased from 5% to 25% (wet weight basis (wb)). When glycerol was added, a further decrease in Tg was obtained. Tg was reduced from 120 to 60 A degrees C and 45 A degrees C for 10% and 20% glycerol, respectively, at a moisture content of 10% (wb). A direct comparison between starches with similar composition showed equal Tg (P > 0.05). The modeling for the control samples (0% glycerol) gave a Delta Cp similar to aEuro parts per thousand 0.4 Jg(-1) K-1 for WMS and RS and similar to 1.9 Jg(-1) K-1 for water. These values can be explained by the well-known Tg dependence on degree of polymerization and molecular weight. When the glycerol concentration was increased, an increase was observed, Delta Cp similar to aEuro parts per thousand 0.6 Jg(-1) K--1,K- for both starches and similar to 2.8 Jg(-1) K-1 for water. This behavior would indicate an overestimation in the plasticizing effect of glycerol due to the possible occurrence of polyol-rich fractions in the extruded samples.
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    Sorption Behavior of Extruded Rice Starch in the Presence of Glycerol
    (Wiley-Blackwell, 2010) Enrione, Javier; Hill, Sandra; Mitchell, John R.; Pedreschi Plasencia, Franco
    The modeling approach to predict the sorption behavior of nonelectrolytic mixtures has been related to moisture content at a specifi c equilibrium relative humidity (ERH) and to the component weight fraction in the system. The work presented here attempts to identify deviations of the predicted sorption profi le of a model system based on rice starch and glycerol. Accurate sorption isotherms (25 ° C) were obtained by using dynamic vapor sorption (DVS) for the ERH range of 0% - 90%. The glass transition temperature (Tg) of the samples was obtained by differential scanning calorimetry (DSC). Sorption studies show a reduction in moisture content for an ERH of 60% in the presence of glycerol. This behavior was represented by a reduction in Guggenheim - Anderson - de Boer (GAB) modeling parameters, the monolayer value (from 8.9% to 6.6%); a reduction in the constant related to the net heat of sorption (from 6.4 to 3.5); and an increase in the constant related to the heat of sorption at the multilayer (from 0.72 to 0.94). The sorption profi les of the starch - glycerol mixtures were also modeled using sorption isotherms and moisture contents from each component. The estimated interaction factor of 1 indicated a reduction in water uptake specifi cally for an ERH of 60%. The 10% and 20% glycerol systems showed a signifi cant increase in independent interaction factors (IIFs) from 0.6 to 0.9, suggesting a relationship between water uptake and the matrix - polyol interaction. This behavior was related to the molecular mobility of the system, as indicated by plotting IIF versus T T g ( T = 25 ° C).