Influence of glycerol on the melting of potato starch

The gelatinization and melting of granular and recrystallized starch have been studied in the presence of low and high levels of glycerol or water by differential scanning calorimetry. The gelatinization onset temperature is increased in the presence of glycerol, whereas the excess gelantinization enthalpy is not affected. A broadening of the transition or change in shape is observed by lowering the amount of plasticizer. The increase of the melting onset temperature by the addition of glycerol is explained by an increase in the activation energy of the melting of the starch crystallites. The rise in activation energy is the result of the higher glass transition temperature of the amorphous phase and by the higher interaction forces of glycerol with the starch polymers. The changes in the shape of the endotherm at low plasticizer content is interpreted as an entropic effect. With less plasticizer the change in entropy during melting is low as a result of the lower mobility and viscosity of the starch polymers and the diluent molecules leading to less conformational freedom.