Study On The Effects Of Starch On The Formation And Aggregation State Of Gluten Protein In Wheat-potato Composite Bread

Potato is an important crop worldwide,including carbohydrates,vitamins,minerals,dietary fiber,etc.In view of the huge yield and rich nutrition of potato,the strategy of transforming potatoes from basic food to nutritious and healthy consumer goods has begun.Potato,as a main raw material of potato bread,can exert its excellent biological values,which strengthens nutritional complementation of bread and meets people’s needs for a balanced diet without changing people’s eating habits.The development of potato bread is in line with the national strategy of potato staple food.However,due to the lack of deep research on potato bread,the core problems in terms of small specific volume and high hardness when addition of high-proportion nutrient-fortified potato powder in bread have not been solved.Therefore,this paper combines the dough structure,processing characteristics and starch-protein interactions to explore the influences of starch on potato bread quality and heat-induced aggregation of gluten protein network by constructing a model dough,which reveals the deterioration mechanism of potato dough.Accordingly,the cellulase and pectinase was used to hydrolyze cellulose and pectin,as a result,regulate the starch properties,improve the quality of high-proportion potato bread,and lay a foundation for the development of other multigrain breads.The main research contents and conclusions are as follows:First,by comparing the effects of different modifiers on the microphysical structure,rheological properties and fermentation properties of the dough,we analyzed the reasons for the decrease in the processing properties of the dough caused by the addition of potato.The structure-functional relationship between the gluten network structure in the dough and the dough processing characteristics was analyzed by laser confocal microscopy（CLSM）in our study.The results show that addition of potato whole flour reduced the continuity and stability of the three-dimensional network of gluten protein.In our study,individual addition of gluten did not effectively improve the processing characteristics of the dough,and it was necessary to synergistically supplement carboxymethyl cellulose（CMC）to promote the cross-linking aggregation between the protein peptide chains through the interaction between the hydrogen bonds and ion bonds between CMC and gluten protein.During this process,the dough formed a biphasic expansion of the"spider silk"three-dimensional network and the potato dough flexibility and ductility were improved.As a result,the bread specific volume increased by42.85%,the hardness decreased by 79.04%.The results prove that the addition of potato whole flour not only dilutes the gluten protein,but also its starch particles in the potato whole powder affects the non-covalent interaction between the gluten protein peptide chains,which changes the aggregation state of the gluten protein,and leads to a decrease in the structural integrity and uniformity of the gluten protein network.In order to systematically study the influence of different starch particle characteristics on the formation and aggregation of gluten network,so as to guide the raw material pretreatment during potato bread preparation,the model dough,including different sources of starch with different size distribution and morphology and gluten,was established.Then,the mechanism of formation of gluten protein in the process of dough modulation was systematically studied.The study shows that the Hausner ratio and Carr’s index of starch particles showed an upward trend with the decrease of starch particle size and the increase of non-spherical coefficient,namely,the fluidity and filling effects of starch particles decreased during this process.Environmental scanning electron microscopy（SEM）and laser confocal microscopy（CLSM）results show that large size of starch particles,which blocked the interaction between protein peptide chains,resulted in the structure of dough rupture of the gluten protein network.In contrast,the small size of starch particles was difficult to effectively support the formation and expansion of gluten protein network,resulting in aggregation of gluten protein.The influence of the internal microstructure of the dough on its macroscopic processing characteristics was studied by dynamic rheology,and it was found that,when the size of starch particles were moderate（especially corn starch particle）,it could be uniformly filled in the gluten protein network,the dough consistency coefficient（K=3.17 Pa·sn）was the smallest,the creep recovery rate（Je/Jmax=66.20%）and the ductility（135 mm）were the largest,which was most suitable for the formation of bread structure.The volume of starch granules has an important influence on the formation of gluten protein network,and its different surface properties also have an important influence on the formation of gluten protein.The surface of starch granules was modified by wet heat treatment,and starch granules with different surface hydrophilicity were prepared.The study found that majority of starch granules still maintained their original granule after wet heat treatment,without obvious collapse and shrinkage.The free sulfhydryl content of the model dough was measured.The results show that,compared with the original starch model dough,the free sulfhydryl content of the corn starch model dough increased by 5.25%,13.44%and 18.36%when the initial moisture content of the wet heat treatment was 20%,25%and 30%,respectively;at the same time,the free thiol content of potato starch model dough increased by 0.93%,4.91%and 5.37%,respectively.In addition,we found that with the increase of the initial moisture content of the hydrothermal treatment,the hydrogen bonds,ionic bonds and hydrophobic interaction between starch-protein molecules presented decrease.Starch particles not only affect the formation of gluten protein network through stacking filling,the surface of starch particles as their contact point with the gluten matrix,and their different surface characteristics may also contribute to the aggregation of gluten protein during the surface mass modulation.In our study,the surface of the starch particles was modified by heat treatment,and the starch granules with different active hydroxyl groups were prepared,then,the model dough was prepared.In addition,the free mercaptols,free amino groups,protein molecular weight distributions and protein secondary structures in the model dough were determined.The results show that the hydroxyl distribution on the surface of the starch particles was changed after heat treatment,resulting in different degrees of decrease in hydrogen bonds,ion bond and hydrophobic interaction between starch-protein molecules,which caused a significant increase in the free thiol and free amino content of the model dough.These alternations lead to a decrease in the stability of the secondary structure of gluten,causing the transformation of theβ-folding structure to the random curl andβ-corner structure,and resulting in an increase in the extractable protein content in the dough and a decrease in the gluten mass（GMP）content.It was confirmed that the weakening of the starch-protein non-covalent interaction is not conducive to covalent crosslinking between gluten protein peptide chains,resulting in changes in the aggregation of gluten proteins.In order to deeply explore the influence of changes in the surface properties of starch particles on the de-folding and heat-induced aggregation of gluten protein during baking,the free mercaptol,free amino,endogenous fluorescence and hydrophobicity of protein surface of model dough during heat treatment were determined.The results showed that,compared with the original starch-gluten model dough,the free mercaptol of the model dough individually contains heat-treated corn starch and potato starch increased by 18.75%and 38.25%,respectively,and the free amino content increased by 52.86%and 14.56%,respectively.In addition,due to the cross-linking aggregation between protein molecules in the model dough after heat treatment,the redshift phenomenon of endogenous fluorescence spectrum at 95°C was weak and the hydrophobicity of the protein surface was high.Finally,through the comparative analysis of protein subunit composition distribution in the heat treatment process by reverse high performance liquid chromatography（RE-HPLC）,it was found that the decline of starch-protein non-covalent interaction changed the process of integratingα/β-γ-alcohol colladin into the gluten protein network at high temperature,and inhibited the formation of cross-linked gluten aggregates.The cell-wall components,such as cellulose and pectin,which adhere to the surface of starch particles in potato whole flour,not only strengthen the adhesion and friction between the particles,but also results in large particle clumps in the starch phase of potato dough,blocking the interactions between protein peptide chains.In addition,cell-wall components also hinder starch-protein non-covalent interactions by steric hindrance and competitive binding of hydrogen bonding sites on the surface of starch particles.Based on the above research,the whole potato powder was treated with cellulase and pectinase,and the particle size distribution,powder fluidity and surface hydrophilicity before and after enzyme treatment were determined.The results showed that after 60 min of enzyme treatment,the D₅₀ of the whole flour reduced by 26.48%,and the ratio of Carr’s index to Hausner decreased by 29.61%and 21.16%,respectively,which effectively improved the accumulation and filling ability of starch in potato whole flour.In addition,after 60 min of enzyme treatment,the surface contact angle of potato whole flour decreased by 48.82%,indicating that the surface hydrophilicity of starch particles significantly improved.Finally,the corn starch with moderate particle size was added to the system,and the quantitative analysis of the gluten protein network in the potato dough by Angio Tool64 software presents that,after the enzyme treatment of 60 min,the protein network length and protein network connection point significantly improved,and finally,the potato bread specific volume increased by 69.31%,the hardness reduced by 64.08%,which significantly enhanced the quality of potato bread.