Rheological and DSC studies of chemically modified starch

The effects of degree of modification on the physico-chemical properties of chemically modified starches (hydroxypropylated potato di-starch phosphates) were studied by dynamic viscoelasticity measurements and differential scanning calorimetry (DSC). Dynamic viscoelastic measurements were performed for 10% pastes of native potato starch and chemically modified potato starches heated at different temperatures. The storage shear modulus (G') and the loss shear modulus (G ") of pastes of modified starches heated at 50 to 100 degrees C for 30 minutes were independent of heating temperature. G' and G " were strongly dependent on the degree of modification. Even a slight modification retarded the retrogradation remarkably. Syneresis of pastes became more conspicuous with increasing level of modification. Transparency of modified starch-pastes was constant at 5 degrees C for 1 week and lower than that of native starch-paste. The endothermic peak of chemically modified starches appeared at 48 to 50 degrees C in the heating DSC curves. The retrogradation phenomena of modified starch were scarcely observed, whilst a considerable retrogradation phenomenon was observed in a native one.