| Noodle is one of the traditional staple foods in China.It is loved by people because of its convenience,multiple dishes and different flavors.Traditional noodles are mostly processed from medium-gluten flour,and the blood glucose rises rapidly after eating,which is not suitable for diabetic patients.Therefore,noodles added with dietary fiber have become a research hotspot in recent years.As a by-product of wheat processing flour,wheat bran dietary fiber has high yield and low value utilization.Its main component is insoluble dietary fiber(IDF),which is easy to bring rough taste to flour products.In this study,the effect of IDF on the quality of noodles was firstly investigated.Then,IDF was chemically modified and its structural characteristics were studied.The effects of modified IDF on the properties of starch and protein in dough were investigated.Finally,the effect of modified IDF on the quality of noodles was investigated,which provided theoretical basis and technical reference for the preparation of high dietary fiber flour products.Firstly,high-purity IDF(purity of 83.35%)was prepared by removing starch and protein from wheat bran with thermostableα-amylase and papain,and its effects on dough rheological properties and noodle quality were studied.The results showed that the water absorption and formation time of dough were positively correlated with the addition of IDF,and the stability time and weakening degree were negatively correlated.With the increase of IDF addition,the tensile resistance of dough increased first and then decreased,and the ductility decreased with time.The results of low-field nuclear magnetic resonance showed that IDF promoted the conversion of deep bound water and free water to weakly bound water in noodles.RVA results showed that IDF could improve the thermal stability of starch,reduce the pasting viscosity and retrogradation value,and inhibit starch aging.When the addition amount of IDF was 6%,the color of noodles was significantly deeper than that of the blank group(P<0.05),the breaking force and the stretching distance were the largest,and the elasticity of noodles was the best.The sensory score was 86.12,which was the closest to the blank group.Secondly,IDF was modified by alkaline hydrogen peroxide method,hydroxypropyl method and esterification method to prepare corresponding modified IDF,which were recorded as AIDF,MIDF and OIDF,and their physical and chemical properties,antioxidant capacity and structural changes were studied.The results showed that the three modification methods improved the water holding capacity,swelling capacity and oil holding capacity of dietary fiber.After modification,the glucose adsorption capacity,nitrite adsorption capacity and cation exchange capacity of IDF were significantly improved.The results of FT-IR showed that the characteristic absorption peaks of functional groups of IDF changed after modification.The absorption peak intensity of AIDF at 1652 cm-1 became weaker,the absorption peak of MIDF near 1051 cm-1 appeared obvious blue shift,and the new C-O absorption peak of OIDF appeared at 1745 cm-1.The results of X-Ray showed that the three modification methods did not change the cellulose crystal form of IDF,which was typical cellulose I type.The results of scanning electron microscopy showed that the surface of modified IDF had more pores and the structure was more loose.Thirdly,the effects of modified IDF on the properties of starch and protein in dough were studied.The DSC results showed that the modified IDF significantly increased the gelatinization starting temperature,peak temperature and termination temperature of starch(P<0.05),and was positively correlated with the addition amount.IDF reduced the gelatinization enthalpy.The results of RVA showed that the peak viscosity,trough viscosity,final viscosity,attenuation value and retrogradation value of starch were negatively correlated with the addition of four kinds of IDF.IDF before and after modification could improve the thermal stability of starch system and inhibit starch aging.The study of starch gel properties showed that the four IDFs could significantly increase the water separation rate of the gel(P<0.05),reduce the freeze-thaw stability,and the water separation rate was positively correlated with the amount of IDF added.With the increase of freeze-thaw times,the water separation rate and hardness of starch gel increased significantly(P<0.05).The hardness of modified IDF-starch gel was lower than that of the original IDF-gel,and the hardness of OIDF-starch gel was the lowest.FT-IR results showed that the modified IDF did not form new chemical bonds with starch molecules,but it was found that IDF and starch interacted through hydrogen bonds.With the increase of the addition amount of the four IDFs,the free sulfhydryl content in the dough increased,and the disulfide bond content increased first and then decreased.Theβ-sheet of gluten protein increased first and then decreased,the random coil andα-helix did not change significantly,and theβ-turn decreased first and then increased.When the addition amount of modified IDF was 10%,theβ-sheet content of AIDF,MIDF and OIDF was the largest,and theβ-turn content was the lowest.The microstructure of gluten showed that the pores of gluten containing modified IDF were more uniform and the structure was more complete,and the structure of OIDF gluten was the best.Finally,compared with the original IDF,the effects of three modified IDF on the quality of fresh noodles were studied.RVA results showed that the peak viscosity,trough viscosity,final viscosity,attenuation value and setback value of the mixed powder were significantly negatively correlated with the addition amount of modified IDF(P<0.05),and the viscosity values of the three modified IDF were higher than those of the unmodified IDF.The results of low field nuclear magnetic resonance showed that the water in the IDF dough mainly existed in the form of weakly bound water.The addition of IDF realized the redistribution of water in the dough.The deep bound water content of the modified IDF was higher than that of the original IDF,and the modification delayed the migration of water in the dough to a certain extent.The optimum cooking time of noodles decreased with the increase of IDF addition,and the cooking time of AIDF,MIDF and OIDF noodles was slightly higher than that of the original IDF.The water absorption rate increased first and then decreased,and the cooking loss rate was significantly positively correlated with the addition amount of IDF(P<0.05).With the increase of IDF addition,the L~*value of the patch gradually decreased,and the a~*and b~*values gradually increased.TPA results showed that the hardness and chewiness of noodles increased significantly with the increase of IDF addition(P<0.05),and the elasticity increased first and then decreased.The modified IDF reached the highest value at 10%addition,and OIDF had the best tensile properties.The results of sensory evaluation showed that when the addition amount was 10%,the noodle scores of AIDF and OIDF groups were 85.52 and 85.56,respectively,which were the closest to the blank group(86.59),and the quality and acceptability of fresh noodles were the highest. |
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