Thermal and dynamic rheology of insoluble starch from basmati rice

Abstract

Insoluble rice starch obtained as a by-product of the sequential solvent extraction of proteins from commercial Basmati rice flour was evaluated for thermal and rheological properties. Differential scanning calorimetry (DSC) was employed to gather data on gelatinization temperature and heat of gelatinization of rice starch at a constant heating rate. A small amplitude oscillation shear rheometer was used to study gel rigidity and other rheological characteristics. Elasticity ( G′) of thermally induced starch gel increased as function of starch concentration and decreased with heating rate. Swelling power (SP), close packing concentration and pasting properties of rice starch were also investigated. Isothermal heating of starch in the temperature range of 70–85 °C exhibited a systematic decrease in elasticity ( G′) with heating time where as a reverse trend was observed above 90 °C. Non-isothermal heating of starch at a linear rate of temperature increase with time exhibited peak elastic modulus ( G′) values at specific temperatures which corresponded to starch gelatinization temperatures as observed by DSC. During non-isothermal starch gelatinization kinetics of rice starch, G′− t data up to peak value were considered and a rate equation was evaluated. A first-order reaction kinetics adequately described the rice starch gelatinization and the process activation energy obtained ranged between 32.3 and 42.2 kJ/mol.