Effect Of Sweet Potato Residue Cellulose With Different Particle Sizes On Dough And Bread Quality And Mechanistic Study

Sweet potato is an important cash crop and starch resource,and a large amount of waste residue is produced in the process of producing sweet potato starch.Sweet potato residue contains about 25%of cellulose dry basis and is a good source of dietary fiber.Sweet potato residue celluloses show significant differences from other types of fibers in terms of soluble dietary fiber content,pectin content,and physical and chemical properties such as water retention and swelling due to their different structural forms and chemical components from other celluloses,and thus they interact in a different way from other celluloses after reconstitution with wheat flour.The addition of cellulose to pasta products can effectively increase the dietary fiber content in pasta products,but cellulose has a greater impact on the internal structure of dough and product texture,and the degree of impact is related to the morphological structure and size differences of celluloses.Ultrafine pulverization is an efficient and emerging physical modification technology that not only makes the particle size of dietary fiber materials smaller,but also helps to fully expose the hydrophilic groups in fiber molecules and improve the physical and functional properties of celluloses,which further affects the quality of the products after reconstitution with wheat flour.In view of this situation,in this study,self-extracted sweet potato residue cellulose（SPRC）was used as the raw material,and SPRC of three particle sizes were obtained by ordinary pulverization,ultra fine pulverization and nano-ball milling.After that,the SPRC of different particle sizes were added into wheat flour at a ratio of 7%to study its effect on the quality of wheat dough and bread as well as the interaction mechanism between gluten protein structure and starch.At the same time,the correlation analysis between SPRC particle size and dough characteristics and bread quality was established.This research provides theoretical guidance and technical support for the reuse of potato residues,and enriches the theory of processing adaptability research of cellulose in pasta products.The main conclusions are as follows.（1）The addition of SPRC had different effects on the rheological properties of wheat reconstituted dough.At the same amount of addition,the ultrafine pulverized sweet potato residue cellulose reconstituted flour showed lower viscosity,lower attenuation values,higher powder properties,tensile properties and viscoelasticity compared with the common powdered sweet potato residue cellulose reconstituted flour.When UP-SPRC was added to wheat flour in smaller amounts（5%and 7%）,the rheological properties of the reconstituted flour showed more stable cross-linkages,and the gluten structure ductility and gluten strength were stronger.Therefore,in order to increase the amount of SPRC added to the dough and to minimize the degree of adverse effects of SPRC on the rheological quality of the dough,7%was chosen as the optimal percentage of SPRC added back to the wheat dough.（2）The particle size volume distribution and structural morphology morphology of SPRC with different particle sizes differed significantly and correlated significantly with the dough property index.The particle size of the three SPRC decreased significantly,especially the d_（0.9）and D_[4,3]particle size values differed significantly.The cellulose of SG₁（Maximum particle size）and SG₂（Intermediate particle size）was mostly honeycomb porous,while the honeycomb porous microcrystalline bundle structure of SG₃（Minimum particle size）disappeared and was distributed in a lamellar structure.There was a significant correlation between the particle size of SPRC and the viscosity,water absorption,tensile properties and thermodynamic properties of wheat dough.The addition of celluloses reduced the stability of wheat dough and increased the water absorption and weakness of reconstituted flour.Compared with SG₁ and SG₂,SG₃reconstituted doughs had lower weakness,shorter formation time,and longer stabilization time.Meanwhile,the tensile properties of the reconstituted doughs improved with the reduction of SPRC particle size.The viscoelasticity of each reconstituted dough was higher than that of wheat dough,and the fluid properties of SG₃ reconstituted dough were better than those of SG₁ and SG₂.In addition,SPRC disrupted the structure and continuity of gluten membrane and the fullness of starch granules,SG₁ and SG₂ thinned the gluten structure,and the continuity of gluten protein structure of SG₃ reconstituted dough was improved.Therefore,SG₃ disrupted the internal organization of the dough to a lesser extent,while the reconstituted dough had higher thermal stability and better quality.（3）Compared with the SG₀ group,the fermentation volume of the bread dough with SPRC addition was reduced and the air-holding property was weaker at the later stage of fermentation than at the earlier stage,while the SPRC bread fermentation performance performed worse with the addition of larger particle size and the specific volume of bread was smaller.During the baking process,the water bound by SPRC was difficult to evaporate,resulting in larger moisture content of bread and low baking loss rate,especially in SG₁ group.The bread with the addition of smaller particle size of SPRC had lower hardness and chewiness and higher elasticity,cohesiveness and recovery.The bread morphology of SG₁ group showed a firm internal tissue with small and few pores and dark color,while the SG₃ group had larger bread size,improved internal structural laxity,larger pores and flatter and smoother gluten film.With the increase of storage period,the hardness of bread showed a tendency to increase and then decrease,and the moisture content of bread decreased.The results of DSC and aging degree measurement showed that SPRC increased the phase transition T_o and T_pof bread,△H increased with the increase of storage days,and the higher content of slow-digesting starch in SG₁and SG₂ groups of bread indicated higher aging degree.（4）With the decrease of the added SPRC particle size,the stretchability,cohesion,disulfide bond content and thermal stability of the gluten protein samples increased,the microstructure morphology was more complete,and the gluten protein water-holding capacity,hardness and elasticity decreased,and the presence or absence of starch granules did not affect the pattern of changes in these properties.The addition of cellulose reduced the gluten proteinα-helix andβ-fold conformations and increased the irregular curl andβ-turned conformation,especially compared with the SG₀,the SG₁ group showed the greatest change,and the WF group showed insignificant differences.The SPRC resulted in greater water holding capacity,hardness and cohesiveness of gluten proteins compared to the addition of wheat fiber.However,the stability and integrity of gluten protein structure formation was better in the SG₃ group than in the WF group as seen from the S-S structure and microscopic morphology of gluten proteins.The addition of fibers decreased the agglutination characteristics and△H of starch.Compared with the SG₀,the WF group showed insignificant changes in the pasting and agglutination characteristics of starch,but the lowest paste viscosity value,followed by SG₃.the△H of starch decreased with the increase of SPRC particle size.The difference in viscoelasticity between starches with different particle sizes of SPRC added was not significant.In a word,SPRC had a greater force on gluten protein than wheat starch in the dough.Both starch granules and larger particle size of SPRC had a greater destructive effect on gluten structural stability and continuity.SG₃ has a certain ameliorating effect on the destructive effect of this gluten network structure.Meanwhile,the microstructural morphological integrity of gluten proteins in the SG₃ group showed superiority over the WF group,which provides a reference pathway for the modification and utilization of SPRC for applications.