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Nonwaxy rice starch was crosslinked using sodium trimetaphosphate and sodium tripolyphosphate to obtain different degrees of crosslinking (9.2, 26.2 and 29.2%). Rice starch suspensions were heated from −40 to 100 °C at 2 °C/min 1) in a Differential Scanning Calorimeter and 2) under a light and polarized light microscope, in order to analyze for glass and/or melting transitions. The size of the starch granules increased with increasing temperature; the onsets for dramatic increase in size were approximately 55 °C for native and control samples and approximately 60 °C for crosslinked samples. A twostep swelling pattern was observed above 55 °C corresponding with the biphasic endothermic peaks as well as the discontinued (biphasic) loss in birefringence (due to heterogeneity in transition temperature). No disruption of granules was observed in any crosslinked samples. The low temperature transition (55–70 °C) involved both a loss in molecular order (possibly also melting) and swelling which were partly inhibited by crosslinking. Crosslinking delayed the gelatinization process (without decreasing total enthalpy) by restricting swelling and reducing the hydration of starch. No evidence of glass transition was observed in any samples studied.

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 transitions 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 crosslinked starch were evident due to restricted swelling and reduced hydration in starch granules. Glass transition temperature (Tg) measured from the derivative curve of heat flow was -3 to -4°C. No significant change in Tg w...

The influence of reaction parameters on the carboxymethylation of rice starches with different amylose contents was investigated. Rice starches with varying amylose contents showed various degrees of susceptibility to the reaction conditions. The maximum degree of substitution (DS) for all three rice starches was obtained under similar reaction conditions which involved a reaction medium consisting of isopropanol–water at the ratio of 90:10, a molar ratio of NaOH:AGU at 1.5 and a reaction temperature and time of 40 °C and 3 h. Under these conditions, the DS for all rice starches was similar; however, when the reaction was performed under conditions using lower NaOH concentration, the effect of starch types on the DS was observed. The results could be explained in terms of the granular/structural features of the different rice starches, their degrees of granular swelling as influenced by the reaction conditions and the accessibility of the etherifying reagents to starch molecules.

Mobility and distribution of water in cassava (rainy and drought crops) and potato starches were studied by solid state and NMR relaxometry as a function of H(2)O and D(2)O contents ranging from 0 to 44% (dry basis). Measurements of relative mobility derived from (2)H solid state NMR were based on relative area and line shape analysis. The narrow peak (mobile component) started to show at 5% and increased with increasing D(2)O content. This increase in mobile fraction was accompanied by a line narrowing. The mobile fractions of deuterons reached a98% level above 15% D(2)O, which is well below the water holding capacity of starch ( approximately 27%) and the previously assigned "glassy-rubbery transition point" (24.3%; Jouppila, K.; Roos, Y. H. The physical state of amorphous corn starch and its impact on crystallization. Carbohydr. Polym. 1997, 32, 95-104). This reconfirms the liquidlike nature of water in the so-called glassy state of starch granules. The plasticization effect of water on starch chains was observed at 14-17% for cassava and potato starches as indicated by the T(1) minimum. This, however, did not seem to relate to the difference observed in swelling among the starches studied.