Effect of heating condition and starch concentration on the structure and properties of freeze-dried rice starch paste

The structure and characteristics of freeze dried rice starch paste were investigated at low starch concentrations (1%, 3% and 5%). The microstructure of samples made at 1% of starch concentration showed a loose filamentous network compared to other concentrations (3% and 5%). Especially the samples prepared at processing conditions above 110 °C and 3% were appeared a coarse honeycomb-like structure. Crystallinity of samples calculated by intensities of X-ray diffraction peaks was very low values (3.3-9.8%). The mechanical properties (hardness, cohesiveness and springiness) of the samples were highly influenced by starch concentration and heating temperature. The relative increment of water absorption index (WAI) according to increasing of heating temperature showed the highest value at 1% of starch concentration, and the heating temperature was analyzed to the important factor affecting WAI and WSI (water solubility index). The digestibility of samples showed an increasing trend with heating temperature regardless of starch concentration. Overall, the important factors influencing the properties of freeze dried rice starch paste were starch concentration and heating temperature.