A concavity property of the viscosity growth curve during alkali gelatinization of rice starch

A qualitative difference between the viscosity–time curves for thermal and strong alkali gelatinization of rice starch was demonstrated using continuous capillary viscometry. During the thermal (60, 70, 75, 80 °C) gelatinization with distilled water, the viscosity growth curves kept a convexity property, in accordance with the past known results. In contrast, the viscosity growth curves for the cold (15, 20 °C) gelatinization with a 0.146 N NaOH solution showed a concavity property in the first half of whole gelatinization process. This result confirmed our previous result having been obtained from batch-type measurement with use of a cone-plate viscometer. On the basis of the first-order reaction hypothesis for gelatinization degree, this novel viscosity growth behavior in cold alkali gelatinization could be described in terms of the mixing rule of viscosity distinct from that had been applied to thermal gelatinization.