Effects of preincubation on the gelatinization of cassava and corn starch suspensions containing sodium hydroxide as a main component of corrugating adhesives

Application: This thermodynamic study clearly showed the properties and gelatinization mechanism of starch granules used for corrugating starch adhesives. The essential properties of starch granules for controlling the practi-cal preparation and use of these adhesives were a considerable stepwise reduction of gelatinization temperature, especially the starting temperature in response to the increase of sodium hydroxide and the stepwise gelatinization progress in response to the rise of surrounding temperature.
Author: Takatoshi Koyakumaru and Hirofumi Nakano
Effects of preincubation on the gelatinization of cassava an
ABSTRACT: Effects of the preincubation temperature and the caustic-ratio, the molar ratio of sodium hydroxide to starch glucose residue, on the gelatinization of cassava starch and corn starch suspensions were studied using differential scanning calorimetry in view of utilization for corrugating adhesives. The gelatinization temperature and enthalpy change of cassava starch suspensions after the preincubation at 30°C decreased as the caustic-ratio increased, similar to those of corn starch ones: The gelatinization starting temperature (Ts) decreased considerably more than the peak temperature and the conclusion temperature (Tc). Although Ts lowered and the width of gelatinization temperature expanded, compared with those of corn starch suspensions, the two starch suspensions with the same half gelatinization transition temperature showed similar gelatinization characteristics of almost the same Ts and Tc. During 1 h-preincubations at 30°C•50°C, the starch granules with Ts that were lowered considerably below each preincubation temperature by sodium hydroxide showed limited gelatinization. The gelatinization transition did not rapidly spread over the whole suspension, but progressed stepwise in response to the increase of the causticratio and the rise of the preincubation temperature. In a prolonged preincubation at a constant temperature, Ts gradually rose at higher caustic-ratios in which stepwise gelatinization commenced. Although the starch gelatinization was irreversible and not in a stable equilibrium state for a long time, we concluded that such stepwise gelatinization progress controlled the practical preparation and use of corrugating adhesives.

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