Effects of adding acids before and after gelatinization on the viscoelasticity of cornstarch pastes

Effects of sour substances (citric acid, acetic acid, lactic acid, malic acid, tartaric acid, and ascorbic acid) on the rheological properties of cornstarch pastes were studied by steady shear and dynamic oscillatory viscoelasticity measurements, intrinsic viscosity measurements, and microscopic observation. The pH of cornstarch dispersion was adjusted between 6.0 and 3.0. The viscosity of the pastes was increased by lowering the pH (between 5.5 and 3.6), while the viscosity of samples with pH below 3.5 decreased further than that of the control (pH 6.3). Hydrolysis of amylose and amylopectin chains occurred by adding sour substances, and led to the decrease in the viscosity at lower pH. However, adding a small amount of sour substances promoted leaching out of amylose and amylopectin chains, and led to the increase in the viscosity. Similar tendencies were observed by adding various sour substances used to adjust pH. No decrease in the viscoelasticity was observed for cornstarch pastes by adding acids at 25 °C after gelatinization.