Rheological and DSC studies of gelatinization of chemically modified starch heated at various temperatures

The effects of the degree of modification and heating temperature on the physico-chemical properties of hydroxypropylated phosphate cross-linked potato starch (HPS) on gelatinization were studied by heating differential scanning calorimetry (DSC), microscopic observation, granule size distribution and dynamic viscoelasticity measurements. The endothermic peak appeared at the temperature from 45 to 46°C for HPS, whereas it appeared at 60°C for native potato starch (NPS) in the heating DSC curves. Dynamic viscoelastic measurements were performed for 5% dispersions of NPS and HPS heated in various temperatures. The HPS granules heated in the temperature range from 50 to 100°C for 30 min did not rupture, and the diameter after heating was strongly dependent on the degree of modification. In contrast NPS granules ruptured gradually on heating above 70°C. The viscoelasticity of heated HPS dispersions were strongly dependent on the degree of modification. The storage shear modulus (Gʹ) and the loss shear modulus (Gʹʹ) of HPS dispersions decreased and became more frequency dependent with an increasing degree of modification. The viscoelasticity of these dispersions heated in the temperature range from 50 to 100°C were almost independent of the heating temperature. On the contrary, the viscoelasticity of NPS dispersions decreased with increasing heating temperature.