Structural transformation of sago starch by heat-moisture and osmotic-pressure treatment

Sago starch was modified by osmotic-pressure treatment (OPT) and heat-moisture treatment (HMT) and physicochemical characteristics were compared. In OPT, sago starch was suspended in saturated sodium sulfate solution and heated for 1 h at 100, 110 and 120 degrees C, corresponding to a calculated osmotic pressure of 32,728, 33,640 and 34,552 kPa (assuming sodium sulfate dissociates completely), respectively, and in HMT, sago starch with 20% moisture content was used. Change of X-ray diffraction pattern from C-type to A-type was obtained for OPT and HMT starch at 110 degrees C and 120 degrees C, respectively. RVA viscograms of both OPT and HMT starch exhibited a decrease of peak and breakdown viscosity but increase of final viscosity and pasting temperature. Onset (TO), peak (T-p), and conclusion temperature (T-c) of gelatinization of both OPT and HMT starch increased significantly with increase of treatment temperature. Biphasic broadening of T-p was observed for HMT starch indicating an inhomogeneous heat transfer during HMT The observed narrow peaks of DSC curves indicated better homogeneity of OPT These properties suggest that OPT starch is more suitable for large-scale production.