The gelatinization and retrogradation of cornstarch gels in the presence of citric acid

The effects of citric acid on the gelatinization and retrogradation for 20 wt% cornstarch gels were studied by differential scanning calorimetry (DSC) measurements, uniaxial compression tests and dynamic viscoelastic measurements. The pH value of cornstarch dispersion was adjusted to between 5.0 and 3.0 by adding citric acid. The pH of gels without citric acid (control) was 6.3. The cornstarch gels with pH value adjusted to 3.0 were brittle, while the values of Young’s modulus and dynamic viscoelasticity were higher than those of other samples. It is thought that hydrolysis of amylose and amylopectin chains by adding citric acid occurred and the length of elastically active chains decreased, also leading to the formation of new networks. It was found that when cornstarch gels with added citric acid were stored, they became brittle, but became hard to deform against small deformation. However, when cornstarch gels with or without citric acid were stored for longer time at 5 °C, the retrogradation ratio estimated by thermal analysis was not affected by the presence of citric acid.