Effects of annealing and heat- moisture treatment on the rice starch physicochemical properties and microstructure

At present,there is little reports about the modification effects of annealing and heat- moisture treatment on the rice starch.In our research,rice starch was modified by annealing and heat- moisture treatment,the effects of annealing and heat- moisture treatment on the rice starch solubility,swelling degree,digestibility,pasting properties,microstructure and crystal structure were compared and analyzed.It was found that,after annealing,the solubility,swelling degree and reducing sugar release rate of rice starch were increased slightly,the starch gel showed higher strength,and it was easier to be pasted,but the thermal stability of rice starch was lower.While after heat- moisture treatment,the solubility,swelling degree and reducing sugar release rate of rice starch was found to be decreased significantly,the strength of its gel was lower,and it was also difficult to be pasted,but its thermal stability was higher and the retrogradation of starch was decreased. X- ray diffraction pattern showed that rice starch modified by these treatments still showed A- type crysatllinity,but its crystallinity was decreased gradually,and after annealing 1 d or being heat- moisture treated for 6 h,it fell significantly.The SEM results showed that,after annealing treatment,the starch angular began to melt,the particles gradually bonded together and formed a longchain line,while after being heat- moisture treated,the starch particles gradually melted and fused.It was clear that the gel strength of starch with high moisture content was higher after heat treatment,and the solubility and swelling power was also better,but the digestibility of starch with low moisture content was lower after heat treatment,and the thermal stability was improved.