Study On Extrusion Properties Of Sorghum Flour And Sorghum-Bean Nutritional Breakfast Powder

Sorghum was one of the important grain resources in our country, but had poor taste, low protein digestibility, still rested on the traditional processing methods in aspects of food. Lacking of systematic deeply reasearch on the processing quality and application properties of sorghum, and lagging to foreign.Extrusion processing was the effective way to develop extrusion food based on grain. It was essential to use twin-screw extrusion technology to discuss systematically the extrusion processing properties of sorghum, and to develop the study on extrusion food of sorghum. The contents and main conclusions of this research were as forlows:Study on the physical and chemical qualites and extrusion properties of three sorghum flours showed that extrusion technology was a better processing way to improve the sorghum quality. The gelatinization degree, WAI, WSI and protein digestibility of extrudates increased significantly, and the content of tannic acid decreased more than 50% after extrusion. Compared with other sorghum extrudates, Liaoning white sorghum extrudates had the lowest bulk density, certain expansion ratio and hardness, and its WSI and the in vitro protein digestibility were obviously highest, and it also had best acceptability by sensory evaluation. Therefore the white sorghum in Liaoning was suitable to extrusion processing.Study on the influence laws of process parameters on sorghum extrudats by single factor experiment showed that the effects of process parameters on die pressure were significant. The effects of the 4th zone temperature on the water solution index and in vitro protein digestibility, the effects of material moisture content on expansion ratio, bulk density, the water solution index and in vitro protein digestibility, the effects of feed rate on all the qualities of the products and the effect of screw speed on bulk density and the water solution index were all significant. Under the process parameters: the 4th zone temperature 150℃, material moisture content 17%, feed rate 300 g/min, and screw speed 275 r/min, in vitro protein digestibility of the products were respectively higher than other conditions, simultaneously other qualities were suitable.Effect of addition bran to sorghum flour on sorghum extrudates was significant. With increase of the bran addition level, the colour of the products deepened, WAI, expansion ratio, and in vitro protein digestibility decreased significantly, bulk density and hardness ( less than 30%), and WSI(higher than 20%) increased significantly. Tannin acid and fat could combined with protein which affected the protein digestibility after extrusion. Tannic acid affected taste of extrudates significantly, and extrudates were bitter when the bran addition level was higher than 15% .Effect of addition broad bean to sorghum flour on sorghum extrudates was significant. With increase of the broad bean addition level, the colour of the products deepened. The changes of expansion ratio, bulk density and WAI were not significant and hardness decreased significantly when the broad bean addition level was less than 30%. Protein digestibility increased significantly, and anti-nutritional factors were damaged. WAI increased significantly and tended to be uniform pre and post extrusion when the broad bean addition level was higher than 30%. Broad bean addition endowed sorghum extrudates with the strong atmosphere of bean flavor. The broad bean addition levels was 20% to 30%, extrudates had strong bean flavor, appropriate aroma , and better quality.The optimum conditions of making sorghum-bean nutritional breakfast power were optimized by using the steepest ascent method and response surface method. The results showed that the effects of the process parameters on viscosity and WAI were not significant, the broad bean addition level correlated linearly with WSI, the regression equation was Y4=11.230769+1.925831X4 , and the effects of the process parameters on the sensory evaluation of products were significant, the model of the quality of the nutritional powder was Y1=7.426715+0.406231x1+0.431541x4-0.247969x12+0.366250x2*x1-0.283316x22-0.513069x32-0.487148x42. The optimum technological parameters were determined as follows: the 4th zone temperature 170.67℃, material moisture18%, screw speed 275 r/min, the broad bean addition level 27.22%. On the optimum conditions, the sensory evaluation value, viscosity, WAI, and WSI of the sorghum-broad bean nutritional breakfast powder was respectively 7.80, 4250.53mPa.s, 6.45g / g, and 12.09%, and the content of protein and fat was respectively 16.55%, 0.32%, so it was a kind of breakfast powder which had low fat and high protein.