Relationship of gelatinization and recrystallization of cross-linked rice to glass transition temperature

Abstract

Nonwaxy rice starch was cross-linked with sodium trimetaphosphate and sodium tripolyphosphate to obtain different degrees of cross-linking (9.2, 26.2, and 29.2%). The objective was to investigate the influence of cross- linking on thermal transitions of rice starch. Starch suspensions (67% moisture) were heated at 2°C/min using differential scanning calorimetry (DSC) to follow melting transition of amylopectin. Biphasic transition were observed at ≃60-95°C in all samples. Melting endotherms of amylopectin shifted to a higher temperature (≤5°C) with an increasing degree of cross- linking, while there was no dramatic change in enthalpy. Recrystallization during aging for 0-15 days was significantly suppressed by cross-linking. The delayed gelatinization and retrogradation in cross-linked starch were evident due to restricted swelling and reduced hydration in starch granules. Glass transition temperature (T(g)) measured from the derivative curve of heat flow was -3 to -4°C. No significant change in T(g) was observed over the storage time studied.