Study On The Change Of Steamed Bread In Steaming Process

Steaming is an important step in steamed bread production,which directly affects the quality of steamed bread.During the steaming process,the volume of steamed bread expands rapidly,and the protein molecules are denatured which forming a gluten network protein with stable structure.Gelatinization of starch absorbs water during this process.Gelatinized starch gel is filled in the protein network structure,forming the basic skeleton of steamed bread,and it has an important influence on the quality of steamed bread.In this paper,we studied the change rules of physical indexes such as mass,volume,specific volume,ratio of height to diameter and texture characteristics of steamed bread during steaming process.Water content,water activity,water distribution,protein component content,protein secondary structure,disulfide bond content,protein molecular weight distribution,protein digestibility in vitro,starch content,starch gelatinization,starch viscosity,starch crystal structure,starch thermal properties,starch digestibility in vitro,and the influence of different steaming conditions on steamed bread quality.The main results are as follows:1.With the steaming process going on,the mass of steamed bread continued to rise,and the volume presented the trend of first rising and then declining.Within 0⁶minutes of steaming,the volume increased rapidly,the growth rate slowed down within 6²5 minutes,and the volume decreased within 25³0 minutes.The change trend of specific volume was the same as that with volume;the height-diameter ratio decreased first,then rised and then decreased again;the hardness and chewiness both show a decreasing increasing decreasing increasing trend.The elasticity and resilience increased first and then decreased,reaching a larger value at 25 minutes of steaming.The heating rate of different parts of steamed bread was different;the temperature near the cortex rised faster,and the temperature near the steamed bread core rised slowly.When steamed for 20 minutes,the temperature of each part reached 100℃.In the early stage of steaming,the inner stomatal structure was large and uneven;with the steaming process,the stomatal structure gradually became small and dense,and very uniform;excessive steaming also made the inner structure of steamed bread worse,resulting in larger stomata,which affected the quality of steamed bread.2.During steaming,the moisture content and water activity of each part of steamed bread showed a significant upward trend.Free water existed in the fresh steamed bread.With the steaming process,free water disappeared rapidly,and the T₂₁and A₂₁1 of each part of steamed bread showed an upward trend,while A₂₂2 showed a downward trend.The total crude protein content in steamed bread was basically unchanged,the extraction rates of albumin,globulin,gliadin and SDS soluble glutenin showed a significant downward trend,and the content of Glutenin macromer increased significantly;the alpha-helix and beta-fold in the secondary structure of protein decreased significantly,while the content of beta-corner and irregular curl increased significantly;the content of disulfide bond increased significantly;the content of high molecular weight gluten eggs increased significantly.The contents of albumin subunits,low molecular weight glutenin subunits,gliadin and albumin decreased significantly,and the digestibility of protein increased significantly in vitro.The total starch content in steamed bread remained unchanged,while amylose content,starch gelatinization degree,peak time and gelatinization temperature,rapid digestible starch（RDS）and slow digestible starch（SDS）showed a significant upward trend;amylopectin content,crystallinity,peak viscosity,minimum viscosity,final viscosity,the initial gelatinization temperature（T_o）,peak gelatinization temperature（Tp）,and slow digestible starch（SDS）of steamed bread starch showed a significant upward trend.The end point gelatinization temperature（Tc）,gelatinization haw（ΔH）,resistant starch（RS）content showed a significant downward trend,and the crystal structure of starch changed from A+V type to V type.3.With the increase of steam pressure,the specific volume,whiteness,elasticity,adhesiveness,resilience and sensory score of steamed bread increased first and then decreased,reaching the maximum at 0.5kPa steam pressure,while the hardness and chewiness of steamed bread decreased first and then increased,reaching the minimum at 0.5kPa steam pressure,indicating that steamed bread quality was better at 0.5kPa steam pressure.In the steaming process,the quality of steamed bread steamed by two different equipments of steaming pot and steaming cabinet was the same.The specific volume,whiteness and sensory score of steamed bread showed the trend of first rising and then declining.The hardness and chewiness of steamed bread showed a trend of increasing decreasing increasing,while the resilience and elasticity showed a trend of rising first and then decreasing.Both devices achieved higher specific volume,whiteness,elasticity,resilience and sensory score in 25 minutes.At this time,the hardness and chewiness of steamed bread were lower,and the quality of steamed bread was better.The change rule of steamed bread with different proofing degree in steaming process was basically the same.During steaming,the mass,volume,specific volume,elasticity,adhesiveness and resilience of steamed bread billets showed an upward trend,while the height-diameter ratio of steamed bread billets showed a decreasing increasing decreasing trend,while the hardness and chewiness of steamed bread billets showed a decreasing increasing decreasing increasing trend.In the process of steaming,the volume,specific volume and elasticity of steamed bread billet proofing 30 minutes and 35 minutes were small.Steamed bread billets proofing45 minutes and 50 minutes were weak and not stand upright.The steamed bread billet proofing 40 minutes has a higher aspect ratio,elasticity and recovery,and the quality of steamed bread was better.