Effect Mechanism Of Dietary Fiber And Ferulic Acid On Steamed Bread Quality And Starch Digestion

Steamed bread is a kind of traditional fermented flour staple food in China,which is popular with consumers.Whole wheat steamed bread is rich in nutrients,but the presence of bran seriously affected the processing characteristics and edible quality of whole wheat steamed bread,and limited the development of whole wheat steamed bread.Domestic and foreign studies on whole wheat steamed bread mostly focus on bran modification,processing methods,and use of additives,etc.,and little consideration is given to the specific mechanism of bran bran components on the quality deterioration and starch digestibility of whole wheat steamed bread.Therefore,this topic studied the influence mechanism of two functional components in bran,insoluble dietary fiber（IDF）and ferulic acid（FA）and their combination（IDF+FA）on the quality of steamed bread and starch digestibility,and proposed the schemes for improving the quality of whole wheat steamed bread and regulating starch digestibility,in order to improve the consumer popularity whole wheat steamed bread and promote the development of whole wheat fermented flour products.The effects of IDF,FA and IDF+FA on the macroscopic quality of steamed bread were discussed.The results showed that with the increase of IDF and FA additions,the specific volume and resilience of steamed bread decreased significantly（p<0.05）,while the hardness,stickiness and chewiness increased significantly（p<0.05）;and the effect of FA on the hardness of steamed bread greater than IDF.In addition,the results of the distribution of gas cells in steamed bread showed that the addition of IDF and FA both resulted in a significant（p<0.05）decrease in the porosity and average cell area of steamed bread,while the cell density increased significantly（p<0.05）with the addition of IDF,but decreased significantly（p<0.05）with the addition of FA.Therefore,both IDF and FA had adverse effects on the quality of steamed bread,and the simultaneous addition of IDF and FA aggravated the deterioration of steamed bread quality.The effects of IDF,FA and IDF+FA on dough properties were discussed.The results of the thermomechanical properties of the mixed powder showed that the addition of IDF significantly（p<0.05）increased stability time and decreased development time of the dough.However,FA significantly（p<0.05）decreased the development time and stability time of dough,and also reduced the degree of weakening of the dough,indicating that FA affected the formation of gluten.The addition of IDF and IDF+FA significantly（p<0.05）decreased the deep bound water and free water content of the dough,and increased the elastic modulus and viscosity modulus of the dough.And the effect of IDF and IDF+FA on the moisture distribution and viscoelasticity of the dough were much greater than those of FA,indicating that the effect of IDF on dough moisture was one of the main reasons for affecting the physical and chemical properties of the dough.The fermentation rheological properties of the dough showed that the addition of IDF,FA and IDF+FA significantly（p<0.05）reduced the fermentation height（Hm）of the dough,hindered the fermentation expansion of the dough,and the effect of FA was more obvious.Quantitative analysis of the dough microstructure showed that the addition of FA and IDF+FA increased the protein area,the total number junctions of protein and the total protein length,resulting in a denser gluten protein network structure.The interaction of IDF,FA and IDF+FA with gluten in steamed bread was investigated.The results showed that the extractable protein in sodium dodecyl sulfate（SDS）supplemented with FA and IDF+FA was significantly（p<0.05）lower than that in the control sample,which promoted the gluten aggregation.A However,the SDS-extractable protein with the addition of FA increased significantly（p<0.05）with the addition of FA,and the free sulfhydryl content also increased significantly（p<0.05）with the addition of FA,indicating that with the addition of FA,the degree of covalent cross-linking polymerization of gluten protein gradually weakened.In addition,the data of gluten protein charge distribution indicated that IDF,FA and IDF+FA could also promote the gluten aggregation by reducing the non-covalent bond（electrostatic repulsion）of gluten protein,and IDF had a greater effect on the electrostatic repulsion of gluten proteins than FA.The investigation of the tertiary structure of gluten protein found that IDF did not change the microenvironment of tryptophan,while the addition of FA increased the polarity of the microenvironment of tryptophan.Therefore,FA and IDF+FA formed an over-aggregated gluten protein network structure by inducing non-disulfide covalent cross-linking of gluten proteins and reducing the electrostatic repulsion of gluten proteins;while IDF hindered the formation of gluten protein network structure through competitive water absorption,steric hindrance and reduction of electrostatic repulsion;both were the main reason for the deterioration of steamed bread quality.The interaction of IDF,FA and IDF+FA with starch in steamed bread and the mechanism of its influence on starch digestibility were discussed.The in vitro starch digestibility of steamed bread found that IDF,FA and IDF+FA could effectively regulate the digestibility of starch.IDF and IDF+FA decreased the content of rapidly digestible starch（RDS）and slowly digestible starch（SDS）,and significantly（p<0.05）increased the content of resistant starch（RS）in steamed bread.However,FA decreased RDS and RS contents and increased SDS contents.The starch-iodine binding capacity showed that the addition of FA significantly reduced the ultraviolet absorption peak intensity of starch-iodine,and significantly（p<0.05）decreased the iodine blue value,indicating that FA inhibited the binding of starch and iodine,which in turn affected the combine between starch and starch.IDF,FA and IDF+FA reduced the Fourier infrared absorption peak intensity of starch at 3600-3000 cm^-1 and 1646 cm^-1,indicating that the O-H stretching vibration of starch was weakened,and the binding of starch and water decreased,indicating that IDF,FA and IDF+FA might be combined with starch through hydrogen bonds,hindering starch water absorption and affecting starch digestion.The X-ray diffraction patterns and Fourier transform infrared spectra showed that the addition of IDF,FA and IDF+FA did not produce new characteristic peaks in the spectra,proving that IDF,FA and IDF+FA passed through non-covalent bonds（with hydrogen bonds predominately）interact with starch.Whole egg liquid/yolk liquid,and whole egg liquid/yolk liquid+xylanase were used to alleviate the excessive aggregation of gluten caused by IDF and FA to improve the quality of whole wheat steamed bread and regulate starch digestibility.The results showed that he four modifiers significantly（p<0.05）increased the specific volume and decreased the hardness of whole wheat steamed bread,and the improvement effect of egg yolk liquid+enzyme was the best.All four modifiers obviously increased the fermentation height Hm and CO₂ production of the dough,and improved the proofing expansion of dough.Whole egg liquid and egg yolk liquid increased the extractable rate of glutenin subunits under reducing conditions.It indicated that egg protein and glutenin subunits formed a protein network structure with extensibility ductility through the exchange reaction of free sulfhydryl-disulfide bonds,overcoming the excessive aggregation of gluten caused by IDF and FA.In addition,all four modifiers effectively regulated the digestibility of starch and increased the nutritional functional properties of whole wheat steamed bread.Whole egg liquid and egg yolk liquid effectively inhibited starch digestion by reducing the content of RDS and increasing the content of SDS and RS,while the enzyme-added samples regulated starch digestion by reducing the content of RDS and RS,and increasing the content of SDS.The results of starch solubility and swelling degree showed that the combination of egg yolk liquid components and starch hindered the enzymatic digestion of starch,thereby reducing the starch digestibility of whole wheat steamed bread.