Effect Of Flour Characteristics On The Quality Of Whole Buckwheat Noodles Prepared By Extrusion

As the staple food with a low glycemic index,buckwheat noodles are favored by more and more consumers,but their problems of quality greatly limit the acceptance of consumers,such as easy-to-break and paste soup.The flour characteristics of raw materials determine the quality of buckwheat noodles.Therefore,the aim of this study is to explore the effects of different varieties of buckwheat and different flours obtained by step grinding of Tartary buckwheat on their noodle quality,so that screening appropriate extrusion processing conditions,and obtaining the whole buckwheat noodles with both health effect and edible qualityFirstly,the differences in nutritional composition and flour characteristics between Tartary buckwheat and common buckwheat were compared.And then,Rapid Visco Analyser,X-ray diffraction,and Scanning Electron Microscope were used to analyze the gelatinization properties,starch crystal structure,and microscopic structure in the 4 kinds of flours made from Tartary buckwheat.Secondly,the parameters of extruded noodles were determined by the whole Tartary buckwheat flour,which retained nutrients intact and are better for health.The cooking quality and texture properties of its extruded noodles were also measured.Finally,it was detected that the cooking quality,texture properties,moisture distribution,crystal structure,and conformation of Tartary buckwheat noodles were affected by frozen treatments(-20°C),as well as the changes in the content and composition of flavonoids and antioxidant activities.The main conclusions of this research were as follows:(1)There were differences in nutritional components and flour properties between common buckwheat and Tartary buckwheat,but this variety difference did not lead to the different cooking quality of noodles.It was found that Tartary buckwheat had higher total flavonoid content than common buckwheat,but opposite in the crude protein and total starch content.In addition,more small size particles and higher content of amylose starch and damaged starch in common buckwheat flour made flour have better solubility.Nonetheless,there was no difference clearly in the swelling power,gelatinization temperature,and rheological properties between Tartary and common buckwheat flour.However,there was no difference obviously in extruded buckwheat noodles quality,neither cooking quality,hardness nor moisture distribution.(2)According to the cooking quality of Tartary buckwheat whole flour noodles,the parameters of extrusion were set as 15 Hz,40% water addition,zone 1: 60-70°C,zone 2: 70-90°C,zone 3: 90-100°C,and zone 4: 60-70°C.(3)A significant difference in nutritional components and flour properties of Tartary Buckwheat flours were determined,including whole,core,bran and yellow flours,which also leads to a significant difference in the quality of extruded noodles.Firstly,crude protein,dietary fiber,and flavonoids were mainly from the bran in Tartary buckwheat,so it was helpful to improve the nutrition of Tartary buckwheat by increasing bran.Additionally,bran also enhanced the damaged starch content and solubility of flour.The swelling power of Tartary buckwheat flour and starch gelatinization viscosity were decreased obviously.Secondly,a close correlation between flour characteristics and noodle quality were observed.The bran in flour increased the water absorption rate and broken rate of Tartary buckwheat noodles while decreased the texture properties such as elasticity,stickiness,and chewability.Scanning electron microscopy showed that the bran fiber enhanced the number of the lamella and loosened the structure of the noodles.This also indicated that bran reduced the structural stability of Tartary buckwheat noodles.(4)Frozen treatment improved the the quality of extruded noodles made from whole Tartary buckwheat.The broken and cooking loss rate of frozen noodles was lower than dried ones while the hardness and stickiness were higher.According to the scanning electron microscope,the surface structure in dried noodles was compact,resulting in the slow diffusion of water during cooking,thus prolonging the cooking time.The lower degree of retrogradation in dried noodles led to a weaker gel structure stability than frozen ones.Moreover,both frozen and dried treatment would decrease the total flavonoid content and antioxidant capacity of Tartary buckwheat noodles.However,the degree of reduction induced by frozen was lower than that by drying.These results indicated that-20°C frozen treatment was an effective way to improve the cooking quality of buckwheat noodles.