Effects Of Pre-heat Treatment On Dough On Its Properties And Frozen Characteristics

Frozen dough technology has promoted the development of the baking industry due to its advantages such as convenience and standardization.However,the frozen dough shows obvious characteristics deterioration after freezing,which will seriously affect the quality of its products.Ice recrystallization is the root reason for the deterioration of frozen dough,which caused the destruction of gluten network structure,the change of starch granule characteristics and the reduction of yeast activity.Heat treatment is a common physical modification method that can be used to improve the quality of dough and its products.Therefore,this study proposed to pre-heat the dough,and studied the effects of this treatment on the basic properties of dough and its frozen characteristics in different frozen storage time.The main findings were as follows:The starch gelatinization degree,?-amylase activity,farinograph and dynamic rheological properties were applied as indicators to study the effects of different pre-heat treatment time(0 min,5 min,10 min and 15 min)on the dough properties.With the extension of pre-heat treatment time,the starch gelatinization degree significantly increased(p<0.05),and the?-amylase activity significantly reduced(p<0.05),while the 5 min and 10 min groups could retain 82.06%and 74.13%of its activity,respectively.For farinograph and dynamic rheological properties,pre-heat treatment increased water absorption and dough formation time,while dough stabilization time,C₂,G'and G''decreased first and then increased,and tan?value increased first and then declined.Different pre-heat treatment time made dough samples represent different mechanical processing properties.The 5 min pre-heated dough exhibited softer and better ductility properties,the 10 min pre-heated dough had similar properties to the control group,while the 15 min pre-heated dough obviously increased the dough elasticity and showed a harder texture.The specific volume,texture,baking color,internal texture structure,baking loss rate and moisture content of bread crumb were used as indicators to investigate the influence of frozen storage time(0,4 and 8 weeks)on the frozen dough baking quality with different pre-heat treatment time.The pre-heat treatment on dough effectively delayed the bread quality deterioration rate caused by freezing,and moderate pre-heat treatment(5 min and 10 min)could improve the frozen dough bread characteristics.After 8-weeks freezing,the specific volume of 5 min and 10 min pre-heated samples were 3.80 cm³/g and 3.77 cm³/g,respectively,which were significantly higher(p<0.05)than the control group(3.47 cm³/g).And the bread crumb hardness of these two groups above were 412.55 g and 404.56 g,respectively,which significantly lower(p<0.05)than the control group(528.66 g).Also,these two pre-heated groups improved the cohesiveness,resilience and chewiness of bread.In addition,the 5 min and 10 min pre-heat treatment groups could retain the golden brown bread crust color and the creamy white bread crumb color after freezing,as well as increase the cell density to obtain a uniform internal texture structure.The 15 min pre-heat treatment group showed the lowest baking loss rate and the rebound moisture content of bread crumb during frozen storage,which had a certain degree of positive influence on the water holding capability and water retention of bread.SEM,dough moisture content,dough water activity,LF-NMR,XRD,RVA,DSC,SE-HPLC,free thiol(SH)content and FTIR were used as characterization methods.And the influence of pre-heat treatment on dough on the microscopic properties of frozen dough was discussed from four aspects of microstructure,moisture state,starch and gluten properties.The SEM results showed that the starch granules in the pre-heated dough lost integrity and formed a paste,thus tightly combined with the gluten matrix.This stronger starch-gluten matrix effectively weakened the destructive effect of frozen storage on gluten network,while the structure remained complete after 8-weeks of frozen storage time.As a whole,the pre-heat treatment reduced the transverse relaxation time T₂ of water molecules in frozen dough,which indicated that water mobility was inhibited.At the same time,the pre-heated samples also limited the negative migration of water during freezing.When the pre-heat treatment time extended to 10 min and 15 min,the direction of water migration even changed,which made water migrate from semi-bound state to bound state.Therefore,pre-heat treatment could reduce the ice recrystallization so as to reduce the damage to frozen dough.The pre-heat treatment on dough caused the starch granules to gelatinize to a greater extent,which was manifested in the reduction of relative crystallinity,gelatinization viscosity and?H,as well as the increase of gelatinization temperature and gelatinization temperature range.In addition,this treatment method reduced the change rate of relative crystallinity and pasting properties before and after frozen storage.The pre-heat treatment caused the aggregation of gluten and the transformation of its secondary structure to a more orderly direction.The specific manifestations were that pre-heat treatment reduced the content of SDS soluble polymer protein(SDS-P),SDS soluble monomer protein(SDS-M)and peptide chain and amino acid(SDS-AA),increased the content of SDS insoluble protein(SDS-I),reduced the content of free SH,increased the content of?-helical structure,and reduced the content of anti-parallel?-sheets,random coils and?-turns.What's more,pre-heat treatment could also effectively slow down the deterioration rate of gluten component during frozen storage.In summary,the pre-heat treatment on dough could reduce the deterioration of starch-gluten matrix during freezing,thereby improving the frozen dough characteristics.