Effects of concentration dependence of retrogradation behaviour of dispersions for native and chemically modified potato starch

The effects of concentration on the retrogradation behaviour and effects of concentration for native potato starch (NPS) and hydroxypropylated and phosphate cross-linked potato starch (HPS) were studied by heating differential scanning calorimetry (DSC), transparency, granule size distribution and dynamic viscoelasticity measurements. DSC and dynamic viscoelasticity measurements showed that the retrogradation of NPS dispersions was far more conspicuous than that of HPS dispersions. Concentration and time dependence of the storage shear modulus G′ for NPS dispersions heated at 60 and 95°C were different, because NPS granules were disintegrated after being heated at 95°C, whilst some of them remained when heated at 60°C. The rate of retrogradation for NPS dispersion heated at 60°C was faster than that heated at 95°C. The concentration dependence of the storage shear modulus G′ at low concentration range was stronger than that at high concentration range because starch granules were fully swollen to fill the space completely above a certain concentration if the starch granules were not ruptured after being heated. On the other hand, the retrogradation phenomena of HPS were scarcely observed by DSC measurements. The granule size, transparency and storage and loss shear moduli of heated HPS dispersions had not changed much during storage at 5°C. Even a slight modification retarded the retrogradation remarkably. The viscoelasticity of starch dispersions was primarily governed by a combination of the volume fraction of the granule and concentration, if the granules of starch were not ruptured after being heated.