Abstract
Differential scanning calorimetry (DSC), at various heating rates (1-30C/ min) and water:starch ratios (0.1:1-4:1), was used to study gelatinization phenomena of sago starch. The results showed that the gelatinization temperature and enthalpy (ΔH) of starches in excess water were 60-77C and 15.5-15.8 J/g, respectively. ΔH of gelatinization remained substantially the same at excess water contents, but decreased significantly beyond a water:starch ratio of 1.3:1. A single endothermic transition (G) that transformed into a double endotherm (G and M 1 ) and only M 1 occurred, respectively, at excess, intermediate and limited water contents. At 50% water content, evidence of the M 1 endotherm was observed, and 85C represented the effective conclusion temperature (T m ) at the end of melting for sago starch. The experimental data were treated thermodynamically by applying an equation describing phase transitions of semi-crystalline polymers. The calculated value for the melting point of the undiluted polymer (T m o ) was 432 K (R 2 =0.96).
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