Inspired by the previous studies on the viscosity growth behavior of rice starch during NaOH gelatinization, we performed continuous capillary viscometry of the dilute dispersions of corn and wheat starches gelatinized in NaOH solutions at room temperatures. We confirmed that the viscosity-time data series of both starches formed sigmoid curves, just like the case of rice starch. The results clearly contrasted to those obtained for the normal gelatinization in hot distilled water, which formed convex curves during the whole process. The growth process of viscosity for cold NaOH gelatinization was described by the kinetic model, composed of the first-order reaction hypothesis for the degree of gelatinization and the fluidity-type mixing rule of viscosity for ungelatinized and gelatinized parts. The present results suggested that cold NaOH gelatinization of starches generally produced viscosity growth curves of a sigmoid type, and were consistent with our concept that the sigmoidal kinetic behavior has a physicochemical origin based on complex formation caused by alkali-starch interactions.
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