Prediction of the glass transition temperature on extruded waxy maize and rice starches in presence of glycerol. http://dx.doi.org/10.1007/s11947-010-0345-1

Abstract

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 ∼170 to ∼25 °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 °C and 45 °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 ΔCp∼0.4 Jg−1 K−1 for WMS and RS and ∼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, ΔCp∼0.6 Jg−1 K−1, for both starches and ∼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.