Study On Extrusion Process And Quality Improvement Of Rice Noodles By Rice Starch

Rice noodles are usually prepared with gelatinization and regeneration process,using indica rice flour as materials.However,rice noodles made from pure indica starch are rarely reported,even though this kind of noodles products are more healthy for people who has kidney due to it's low protein content.In this study,the indica rice starch was used for the preparation of low-protein content rice starch noodles,and the process of this noodles was researched by twin-screw extrusion technology.Based on the analysis about the effect of hydrothermal and annealing treatment on the starch properties,the quality of indica rice starch noodles was enhanced.The effects of moisture content,gelatinization and molding zone temperature,and screw speed on sensory quality,cooking properties and texture characteristics of rice starch noodle were investigated.The results showed that the cooking loss and broken rate of cooked rice noodles were the lowest,which were respectively 18.76% and 8.67% when the water content was 38%,the gelatinization zone temperature was 92.5°C,the molding zone temperature was 85°C and the screw speed was 95 r/min.The sensory score was 80.50.Also,the starch rice noodles showed good texture characteristics under this condition.Taking amylose content,swelling power and solubility as the index,the optimal condition of was determined.After heat-moisture treatment for 1.5 h at 120 °C with 20% moisture content,the solubility and swelling power of treated starch were reduced to the lowest(16.56% and 10.52 g/g),and the amylose content reached the highest level(24.30%),which was more suitable for preparation of rice noodles.Compared to the untreated starch,the morphology of the treated starch showed no significant change,the crystalline pattern remained type A,and the relative crystallinity increased from 19.18% to 23.52%.The pasting viscosity,setback and breakdown value decreased while the gelatinization temperature and enthalpy significantly increased after treatment(p<0.05).The whiteness value of rice starch decreased from 90.20 to 80.30,and the hardness,springiness and chewiness of gel showed an increasing trend.Rice starch noodle prepared with mixed starch which was added 20%(w/w)treated starch had a sensory score of 90.20,similar to that of commercial rice noodles.The cooking loss and broken rate of cooked noodles were 9.92% and 2.89%,which met the local rice noodle standard.The hardness value was 835.23 g,the elasticity was 0.97 and the shear peak area was 308.61 g·s,indicating that the texture characteristics of this products improved greatly.In the research of annealing treatment,the amylose content,swelling power and solubility were also set as factors to research the optimal condition.On the basis of single factor and orthogonal experiments,the optimum annealed conditions were treatment temperature 55°C,treatment time 16 h,and moisture content 57.5%.The results illustrated that the solubility and swelling power of annealed rice starch decreased to 14.35% and 10.09 g/g,respectively,and the amylose content increased to 24.13%,meanwhile its processing characteristic was improved.After annealing treatment,the morphology of rice starch showed no significant change,the crystalline pattern remained type A,and the relative crystallinity increased to 23.93%.Comparing with the untreated starch,the pasting viscosity,setback and breakdown value of annealed starch decreased while the gelatinization temperature and enthalpy increased.At the same time,the whiteness declined from 90.20 to 84.95.The hardness,springiness and chewiness of gel were enlarged.When the annealed rice starch content reached to 40%(w/w),the sensory score was 92.00,slightly higher than that of commercial rice noodles.At this point,the cooking loss and broken rate reduced to 8.89% and 3.23%,respectively,which met the local rice noodle standards.Furthermore,the texture properties of starch noodles were also improved greatly,since the remarkable increase of hardness,springiness,and shear peak area(p<0.05).The correlation between physicochemical properties of rice starch and qualities of rice starch noodles was also researched.The physicochemical properties of rice starch mainly included amylose content,solubility,swelling power,pasting properties,gel properties and whiteness.The qualities of rice starch noodles included cooking qualities,sensory qualities and texture properties.These remarkable correlation indicated that it was direct and effective to improve the qualities of rice starch noodles by modifying rice starch.