Effects Of Proofing Process On The Properties Of Chinese Steamed Bread

Proofing is an important link in the process of steamed bread making.Steamed bread dough would take a series of complex physical and chemical,biochemical reactions,affecting the texture characteristics and sensory characteristics of the steamed bread.The degree of proofing is closely related to the quality of steamed bread.Based on the changes of starch,protein and microbes in the proofing process of steamed bread,we explored the impact of proofing process on the components of the steamed bread dough.Then combined with the change of the internal components of the steamed bread in the proofing process,the effects of proofing process on the rheological properties of steamed bread were investigated.Combined with the changes of basic steamed bread quality,the relationship between the proofing process and the quality of steamed bread was explored.These studies aim to provide a theoretical basis for the industrial production of steamed bread.Main results were as following.(1)As the proofing time of the steamed bread dough was increased,the peak viscosity,low viscosity and the final viscosity of starch gelatinization were decreased.The change of final viscosity was most remarkable.Proofing can improve the gel properties,but had little effect on the degree of swelling and solubility of starch.In the proofing process of steamed bread dough,part of the gluten protein structure was destroyed,wet gluten content and gluten index decreased.The content of ?-helix,?-sheet,and ?-turn decreased,while random coil increased.The protein content in the fermentation broth and amino acid content in the steamed bread were increased.Yeast and lactic acid bacteria rapid proliferation in dough,pH decreased and TTA increased.Protease activity increased,while soluble solids content,reducing sugar and total sugar content increased.Proofing process produced a lot of water,water migration active,moisture content and the proportion of free water increased.(2)In the proofing process of steamed bread dough,proofing time and proofing temperature were the main influence factors.The influence of the proofing humidity is relatively small.During the proofing process,the rheological properties of the dough changed significantly.With the increase of proofing time and temperature,internal temperature and elongation of dough increased,density and tensile fracture force of dough decreased.Proofing humidity mainly affected dough surface properties.40%RH-60%RH proofing humidity caused surface cracks of dough,reduce internal temperature and elongation of dough increased,density of dough decreased.When the temperature was higher than 35 ?,after 90 min proofing,stretch distance increased firstly and then decreased.(3)According to the single factor test results,we designed the Central-Composite center combination test to measure the whiteness,specific volume and sensory score of steamed bread.The whiteness of steamed bread would be affected by factors in the descending order as proofing time,proofing temperature,proofing humidity;while that of the specific volume of steamed bread as proofing time,proofing temperature,proofing humidity;For the sensory score of steamed bread,the order was proofing temperature,proofing time,proofing humidity.For different evaluations,there were some interactions between the three factors,not a simple linear relationship.The results can provide a reference for the production of steamed bread.(4)Texture profile analysis of steamed bread(TPA)showed that different proofing processes have significant effect on the quality of steamed bread.When the proofing is not enough,adhesiveness and chewiness increased,springiness and resilience decreased.When the proofing is enough,hardness and chewiness increased,springiness and resilience also decreased.The sensory score of the steamed bread is the same as the TPA experiment result.Therefore,the stenmed bread quality can be evaluated by the sensory score of steamed bread.The optimum conditions were: proofing time 60 min,proofing humidity 80%RH and proofing temperature 36?.(5)When the sensory score of the bread is higher than 85.0 points,removed the maximum and the lowest value of the steamed bread whiteness and specific volume,the range of steamed bread whiteness is 51.53-52.66 and the specific volume of steamed bread is 2.122-2.233 g/m L.