Classification and kinetic analysis of viscosity growth processes for NaOH-gelatinized rice starches

Using capillary viscometry, viscosity growth processes were studied for non-glutinous rice starches gelatinized with different NaOH solution concentrations. The viscosity–time data series generally conformed to sigmoid curves with an arbitrary inflection point (IP) for each curve, and were analyzed using a kinetic model that incorporated a first-order reaction rate equation and a mixing rule of a power-law type. The shapes of curves were classified with the exponent ? or the ratio ?*/?G, where ?* and ?G were viscosities at IP and at equilibrium, respectively. It was argued that these parameters were related to the complex formation arising from NaOH-starch interactions. The rate constant K defined uniformly for an entire process increased with NaOH concentration and was power-law dependent. Furthermore, it was suggested that gelatinization evolved non-uniformly over time. A non-uniform analysis was then performed by disassembling the entire process into several elementary stages and revealed the evolutionary process for K.