Rheological studies of Hydroxypropylated and Cross-linked Potato Starch

Abstract

The characteristics of hydroxypropylated phosphate cross-linked potato starch (HPS) were studied by differential scanning calorimetry (DSC), granule size distribution and dynamic viscoelasticity measurements. The endothermic peak appeared at the temperature range from 48°C to 50°C for HPS, whereas it appeared at 61°C for native potato starch (NPS) in the heating DSC curves. The viscoelasticity of heated HPS dispersions was strongly dependent on the degree of modification. Dynamic viscoelastic measurements were performed for 5% dispersions of NPS and HPS heated at various temperatures. The HPS granules heated at the temperature range from 50°C to 100°C for 30 min were not ruptured, and diameters of HPS granules after being heated were strongly dependent on the degree of modification. NPS granules were fully swollen and then ruptured gradually on heating above 70°C. The storage shear modulus (G’) and the loss shear modulus (G”) of HPS dispersions decreased and became more frequency dependent with increasing degree of modification, whereas the viscoelasticity of HPS dispersions heated at the temperature range from 50°C to 100°C were almost independent of heating temperature. On the other hand, G’ and G” of NPS dispersions became smaller with increasing temperature of heat treatment. The retrogradation of chemically modified starch were scarcely observed in the heating DSC curves, whilst considerable retrogradation was observed in the native one. It was shown that even a slight modification retarded the retrogradation remarkably.