Study On The Effect Of Twin-screw Extruded Rice Flour On The Quality Characteristics Of Steamed Rice Bread

Due to the weak gel structure formed by rice and the poor quality of steam rice bread made from pure rice flour,the improvement of rice cake quality is a field worthy of attention in the research of rice products.At present,the research on improving the quality of rice steam bread mainly focuses on adding hydrophilic colloid,emulsifier,polysaccharide and other exogenous substances to improve the gelatinous texture of rice steam bread.In this study,extrusion processing to prepare rice flour,and adding extruded rice flour to make steam rice bread.To explore the modification of rice flour by extrusion treatment and the effect of extrusion powder addition on the characteristics of rice gel and its mechanism.It provides a theoretical basis for the improvement of the quality of gluten-free steam rice bread.In order to obtain the best processing conditions of extruded rice flour,extruded rice flour（ERF）was prepared with rice flour（RF）as raw material to reflect the specific volume of gel structure and tissue structure of steam rice bread（SRB）as the optimization index.Water absorption index as the reference index,using single factor and orthogonal experiment to determine the optimum technological parameters of extruded rice flour.The extrusion process parameters were determined as follows:the water content of the material was 22%,the temperature of the three zones was 130℃,and the host frequency was 17 Hz.,and the specific volume of adding 5.0%extruded rice flour to Buhler milled rice flour（BRF）to make steam rice bread is up to 1.97 g/m L.After extrusion treatment,there are almost no complete starch particles in the rice flour,damaged macromolecular substances,the water retention capacity of the rice flour is increased,and the heat treatment at 20-120°C has little effect on the extruded rice flour.After extrusion,rice starch was cracked,but no new functional groups and chemical bonds were produced in the extruded rice flour,and the crystal form of rice flour changed from A type to V type after extrusion,and the cleavage effect of extrusion on pullulan molecules led to a decrease in the crystallinity of rice flour.After extrusion,rice flour gelatinize,and based on the change of hydration characteristics of extruded rice flour,The extruded modified rice flour was added to the Buhler milling rice flour,and the mechanism of extruded rice flour added to the steam rice bread to make rice flour was studied.The RVA results showed that the peak viscosity,valley viscosity and rejuvenation value of rice flour gel significantly reduced after the addition of extruded rice flour.The DSC results showed that the peak temperature of the rice paste system increased significantly after the addition of extrusive powder,and the enthalpy of gelatinization was opposite.The addition of extrusive powder decreased the thermal stability of the rice paste system.The dynamic frequency scanning results showed that the flow of the rice flour gel enhanced,and the energy storage modulus G′and the loss modulus G′′of the mixed rice flour gel decreased.The results of fermentation volume and fermentation rheology of rice batter showed that adding appropriate amount of extruded rice flour increased yeast gas production and improved dough gas holding,but too much extruded rice flour resulted in decreased yeast gas production and too small fermentation volume.The dynamic temperature scanning results of rice batter showed that the storage modulus and loss modulus of rice batter decreased,but the loss tangent increased,and the extrusion rice flour added increased the fluidity of rice batter during the hot gelatinization of starch.In order to confirm that the addition of extruded rice flour can improve the gel structure of rice starch,the quality changes of steam rice bread investigated.The microstructure showed that the connection between the pores of the steam rice bread with extruded rice flour was not easy to break,the stomatal aggregation reduced,and the tissue structure became better,but when the extruded rice flour added to 12.5%,the internal pores of the steam rice bread significantly reduced.With the increase of the amount of extruded rice flour,R_1047/1022and R_1022/998 presents an inverted"V"change,and the maximum value was reached in the city where the addition amount was 5.0%,and the larger the proportion of crystallization area,the obvious regeneration.Diffraction peaks appeared near the diffraction angle of 2θof 17°and20°,and the steam rice bread showed B-type and V-type polymorphism during aging.The hardness and chew ability of steam rice bread with 2.5%extrusion rice flour added were the largest,and then gradually decreased with the increase of extrusion rice flour.The restoration,cohesion and elasticity of steam rice bread improved by the addition of extruded rice flour.After adding extruded rice flour,the brightness of steam rice bread L*increased,but the amount of extruded rice flour added was 10.0、12.5%,and the yellow color of the skin of steam rice bread became significantly darker.With the increase of the amount added,the specific volume of steam rice bread increases,and the maximum specific volume can reach2g/m L.The porosity of steam rice bread with extruded rice flour decreased,the pore density increased,and the pore size decreased.The addition of extruded rice flour increased the scores of tissue,aroma,color and taste of steam rice bread,and the score of steam rice bread with7.5%of extruded rice flour added was the highest.