Understanding The Change Mechanism Of Starch Characteristics Isolated From Frozen Storaged Dough And Their Effect On Steamed Bread Quality

At present,frozen storage is favored for its advantages of safety,convenience,and low cost,which has gradually become a key technical means for the standardization and large-scale production of the flour industry(such as bread,steamed buns and dumplings).However,the formation and recrystallization of ice crystals in the frozen dough storage process can lead to a series of undesirable changes in the dough,which seriously affect the quality of the product and restricts the development of frozen dough.At present,the research on the quality deterioration of frozen dough is mainly focused on the damage of gluten network and yeast inactivation,but the mechanism of other components of frozen dough(such as starch)is still lack of in-depth exploration and rule summary.Therefore,this topic is expected to find out the mechanism of the change of physicochemical properties of starch isolated from the frozen dough.by studying the starch multi-scale structure and physical and chemical properties.The dough was prepared by the method of dough reorganization to explore the effect of frozen wheat starch on the quality of steamed bread and to clarify the relationship between starch components and the deterioration of steamed bread quality during the storage of frozen dough which can provide theoretical basis and technical support for the development of high-quality quick-frozen flour products.The main conclusions are as follows:First of all,studying the effects of different freezing treatments on the quality of starch and steamed bread,by changing the storage conditions of frozen dough.That is to say,the dough was processed in three different freezing storage methods,namely: The dough was frozen at-20 �C for different times(0 days,15 days,30 days,45 days,60 days),and starch was extracted;Under different freezing storage environment conditions(-20 �C,-40 �C,-60 �C and-80 �C),the dough center temperature was reduced to-20 �C at different freezing speeds,and then store at-18 �C for 7 days,extract starch;The dough was processed with different freeze-thaw cycles(0,2,6,and 10 times),extract starch.Then the extracted starch was mixed with gluten to get the recombination wheat flour,and steamed bread was made.The effect of frozen starch on the specific volume of recombination steamed bread was investigated.The results showed that the specific volume of steamed bread became smaller and smaller with the increase of storage time.After 60 days of storage,the specific volume of steamed bread decreased to 1.16 m L/g.The lower the freezing rate,the smaller the specific volume and the worse the quality of steamed bread.For example,when frozen at-20 �C,the specific volume of the recombined steamed bread was 1.06 m L/g.With the increase of the number of freeze-thaw cycles,the specific volume of steamed bread decreased gradually.After 10 freeze-thaw cycles,the specific volume of steamed bread decreased to 0.9 m L/g.The results showed that the dough treated by freezethaw cycles had the greatest influence on the quality of steamed bread,and with the increase of freeze-thaw cycles,the quality of steamed bread became deteriorated more serious.Secondly,the effects of freeze-thaw cycles on the structure and physicochemical properties of wheat starch were investigated by using modern analytical techniques from multiple angles and multiple scales.The results showed that the freezing and thawing process of ice crystal melting and recrystallization can lead to depression,holes,aggregation of wheat starch particles and decreased the semicrystalline slice thickness,relative crystallinity and regularity of the arrangement,increased the short-range disorder,the double helix structure unwinding.And with the increase of freeze-thaw cycles times,the destruction of the multi-scale structure more apparent.After the freeze-thaw cycle,the pores on the surface of the starch granules and the looseness of the molecular ordered structure promote the penetration of water molecules into the granules and the combination of starch chains and water molecules,thereby increasing the swelling,solubility,peak viscosity,retrogradation value and final viscosity of starch,forming a weaker network structure,which is more susceptible to damage from the outside world.And as the number of freeze-thaw cycles increases,the trend becomes more obvious.Finally,the effect of freeze-thaw starch on the quality of reconstituted steamed bread was explored,and the relationship between starch and steamed bread quality was established.The results showed that after the combination of frozen-thawed starch and gluten,the gelatinization temperature decreased,the elastic modulus and viscosity modulus of the recombined powder increased,and the gluten network continuity of the reconstituted dough decreased.The protein phase separates,thereby weakening the ability to form the gluten protein network structure.In addition,the specific volume and elasticity of the steamed bread prepared by freeze-thaw starch showed a downward trend,but the hardness,chewiness and viscosity increased,indicating that the freeze-thaw cycle treatment can deteriorate the quality of steamed bread.On the one hand,it may be due to the destruction of granular structure and molecular order structure of freezethaw starch,resulting in the starch with high combining ability and strong water swelling capacity,prone to starch molecular chain rearrangement,steamed bread hardness increased.On the other hand,freeze-thaw treatment can destroy the granularity integrity and rigidity of starch,reduce the interface stability of "starch-gluten matrix",weaken the gas holding capacity of steamed bread,and thus make the volume of steamed bread shrink and collapse,and deteriorate its quality.