| Red bean steamed bun is one of the most popular staple foods in China for its sweet and delicious taste and unique flavor.The frozen pre-fermented Red bean steamed bun dough can effectively solve the problems such as product cracking,poor taste,short shelf life and so on.However,in the process of actual production,transportation and sales,the quality deterioration of pre-fermented frozen Red bean steamed bun dough caused by frozen storage and freeze-thaw cycle,which affected its industrialization development.Therefore,this paper focuses on the changes of dough and red bean stuffing characteristics and product quality during freeze-thaw cycles treatment of frozen pre-fermented Red bean steamed bun dough.Furthermore,protein and starch were extracted from dough,and the changes of functional properties and morphological structure of these two components during freezing and thawing were analyzed,and the relationship between main components and quality deterioration of frozen dough was clarified.The main results were as follows:Firstly,the water migration,thermodynamics,rheology and microstructure of dough and red bean stuffing were studied.The nutrition composition,water fluidity,cooking quality,texture,color,flavor and sensory quality of Red bean steamed bun were analyzed.The moisture content of dough decreased gradually,while that of red bean stuffing increased,the strong binding water(A21)of dough and red bean stuffing decreased and the fluidity of water increased,while the frozen water(Fw)content of dough and red bean stuffing increased significantly.The gelatinization enthalpy(?H)of the dough decreased gradually,the viscoelasticity of the dough decreased,and the loss angle(tan 8)increased after freezing and thawing.After 3 cycles,the network structure fragments and pores increased,and the network structure fracture tended to be obvious.In addition,the freeze-thaw cycles significantly affected the edible quality of Red bean steamed bun products(p<0.05).Compared with the control,the protein,fat and water content decreased after freeze-thaw treatment,while the total starch content increased,and the ash content was the highest after 2 cycles.The digestive characteristics of Red bean steamed bun showed that the 5 cycles had the highest estimated glycemic index(eGI).The bound water gradually changed into weakly bound water,and the water activity increased.In addition,the freeze-thaw cycles led to the deterioration of crust,stuffing color and cooking quality,and the content of flavor substances decreased significantly.The internal pores of the products became larger and sparse after 3 cycles,and the sensory quality was the worst after 5 cycles.Secondly,the protein components were extracted from the frozen Red bean steamed bun dough treated by freeze-thaw cycles.The molecular weight distribution,secondary structure,GMP similarity content,free sulfhydryl(SH)content,water holding capacity,frozen water content,thermodynamic and rheological properties of frozen Red bean steamed bun dough.Combined with the whole protein and graded protein figure,it was found that the protein polymer changed after freezing and thawing for 3 cycles,and the macromolecular proteins were randomly depolymerized into lower molecular weight polymers.Freezing and thawing decreased the proportion of more ordered ?-helix and ?-rotation,which led to the decrease of protein structure order.The similar content of GMP decreased,and decreased to 4.29%after 5 cycles.Due to the breaking of disulfide bond during freeze-thaw cycles,the content of SH increased.After 5 cycles,the water holding capacity of gluten protein decreased by 43.84%,while freezing-thawing led to the increase in gluten protein Fw content.In addition,freezing-thawing significantly decreased the peak temperature(Tp),?H and viscoelastic properties of gluten.The correlation analysis between protein and dough quality showed that there was a significant positive correlation between ?-corner structure and A21,the approximate content of GMP was significantly correlated with volume and hardness,and the effects of freezing-thawing on Fw and viscoelasticity of gluten protein were significantly higher than dough.Finally,starch was extracted from frozen Red bean steamed bun dough,and the effects of freeze-thaw cycle on the starch structure and physical and chemical properties were studied.The results shows,the amylose content decreased,and after 5 cycles,the amylose content decreased by 13.69%,while the damaged starch content increased gradually.The water-holding capacity of starch showed that the water-holding capacity of starch frozen-thawed for 3 cycles was the highest.The solubility and expansibility of starch increased gradually.Thermal properties showed that freeze-thaw cycling treatment also significantly increased the To,Tc,Tp and ?H,indicating that repeated freeze-thaw resulted in the formation of more double helix ordered structure in starch granules.After 4 cycles,the RC of starch increased by 13.6%,the short-range ordered structure of starch changed irregularly,R1045/1022 had an obvious positive correlation with RC(r=0.84,p<0.05).With the increase of freeze-thaw cycles,the trend of depression and deformation of starch granule structure is more obvious,and the number of pores is increased and the distribution is uneven.The content of SDS decreased gradually,while the content of RDS and RS increased gradually.The correlation analysis between starch and dough quality showed that the content of damaged starch was significantly correlated with specific volume and hardness,and the change trend of their microstructure was the same,and the gelatinization properties of starch changed significantly after freeze-thaw treatment,there was no significant correlation in digestibility.In summary,the quality of pre-fermented Red bean steamed buns deteriorated during freeze-thaw cycles,and through the exploration of protein and starch components in dough,the basic theoretical basis was provided for further improving dough quality from the point of view of component deterioration. |
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