Study On Nutritional Compound Of Sweet Buckwheat Flour And Quality Of Its Dough And Steamed Bread

Buckwheat is a kind of food with high nutritional value and medicinal function,but its processing performance is poor because of the lack of gluten protein.In this study,sweet buckwheat flour with higher nutritional value was used as the based flour.There are some disadvantages of buckwheat flour such as methionine is the first limiting amino acid and the protein digestibility is low.To improve these disadvantages,the sweet buckwheat flour was mixed with SPI,soybean flour and sesame flour to obtain high digestion nutrition flour and high INQ nutrition flour.The protein in vitro digestibility and protein nutrition quality index were used as indicators to detect the properties of the compound flour.On this basis,xanthan gum,TGase and Vc were added to the compound flour to study the effects of three quality improves on the dough quality such as gelatinization characteristics,texture characteristics and dynamic rheological characteristics.The effect mechanism of quality improves on dough was measured by the detection of free sulfhydryl groups,protein secondary structure and microstructure.The effect of quality improves on the specific volume,sensory evaluation,texture characteristics and aging characteristics of steamed bread were explored.The main results are as follows:The sweet buckwheat flour was compounded and optimized according to the nutritional quality index(INQ)and the in vitro digestibility of protein,the nutritional compound flour proportioning plan was finally obtained.The formula of HIF was 72% sweet buckwheat flour,6% SPI,12% soybean flour and 10% sesame flour.The INQ and the protein digestibility in vitro of the nutrient compound flour which was made according to the formula were 1.47 and 91.00% respectively.The HDF formula was 77% sweet buckwheat flour,4% SPI,6% soybean flour and 13% sesame flour.The INQ and the protein digestibility in vitro of the nutrient compound flour which was made according to the formula were 1.23 and 95.66% respectively.Compared with pure sweet buckwheat flour,the content of protein,fat,ash and dietary fiber in the two nutritional compound flours were significantly increased.Among them,the content of protein(19.93%),fat(5.17%)and dietary fiber(9.43%)in HIF was the highest.The restrictive amino acids composition of the sweet buckwheat nutritional compound flour were not changed,which were still methionine and threonine.But the amino acid composition of compound flour was more balanced and the protein quality was higher than sweet buckwheat.Compared with pure sweet buckwheat flour,the brightness of the nutritional compound flour was significantly reduced,and the yellowness was significantly increased.The water absorption index and swelling potential of the compound flour were significantly reduced;The water solubility index and the combined water capacity were increased significantly,but there was no significant difference between compound flours.The peak viscosity and setback value of compound flours were reduced significantly;The gelatinization temperature and the gelatinization time were increased,which indicated the compound flours were difficult to paste and aging.Xanthan gum,TGase and Vc could reduce the breakdown value and setback value of compound flour but xanthan gum and TGase have better effects on inhibiting compound flour aging.The addition of xanthan gum enhanced the hardness and adhesion of the compound flour dough,and reduced the cohesiveness.The addition of TGase significantly enhanced the hardness,adhesion and cohesiveness of the compound flour dough.The addition of Vc enhanced the cohesiveness of the dough,but reduced the hardness and adhesion of the dough,showed the ability to soften the dough.With the increased of the amount of quality improves,the G 'and G "of the two compound flour doughs increased first and then decreased.Three kinds of quality improves all made the tan ? of the compound flour dough decreased and the polymerization degree of dough increased.The quality improves made the free sulfhydryl groups in the dough form a disulfide bond,which transformed the protein secondary structure into a more ordered ?-helix,but when the amount of TGase and Vc was higher,the free thiol content in the dough increased,the ?-helix content decreased,and the dough quality decreased.Scanning electron microscopy results also showed that the quality improves made the protein structure more orderly,the degree of dough surface collapse was reduced,and the dough structure was more compact.The effect of quality improves on the specific volume,sensory score and elasticity of high-INQ flour steamed breads were insignificantly.With the addition amount of xanthan gum and TGase increased,the hardness and gumminess of the steamed bread first decreased and then increased.Vc could reduce the hardness and gumminess of steamed breads,but there was no significant difference between different addition amounts.Compared with pure sweet buckwheat steamed breads,the quality improve reduced the hardness and gumminess of HIF steamed breads and increased the cohesiveness.The quality improve had no significant effects on the aging rates of HIF steamed breads within 0-30 min,but had significant inhibitory effects on the aging rates of steamed breads within 30 to 60 minutes.