Effect of frying on the pasting and rheological properties of normal maize starch

Normal maize starch (NMS) with various water content was subjected to high temperature in the oil phase to mimic the frying process. The structure and physicochemical properties of the fried starchy samples were investigated. Frying induced the reduction in the swelling power, solubility, the amount of leached amylose, and the molecular weight of starch. Rapid visco-analysis (RVA) revealed the partial gelatinization and limited swelling of starch granules after frying treatment. The effect of frying on the pasting properties of starch was dependent on the water content. Creep curves were fitted with the Burgers model and results showed that the fried samples exhibited higher values of instantaneous creep compliance (J0) and viscoelastic creep compliance (Jm), whereas lower values of zero-shear viscosity (η0) as compared with those of native NMS. The low storage modulus (G′) and low loss modulus (G″) form dynamic viscoelasticity measurements indicated that the fried starch pastes exhibited viscoelastic properties that are inferior to those of native NMS paste. Flow state tests showed that fried starch pastes were less thixotropic than was native NMS. Present work confirmed the inhibitory effect of frying on starch granule swelling and starch molecules leaching. The formation of gelatinization layer near the surface of starch granules and the possible molecular degradation during frying were hypothesized to be responsible for the alterations of the pasting and rheological properties of starch.