Study On The Process Of Thermal History And Its Effect On The Edible Quality Of Baozi

Baozi is a traditional steamed food,formed by fermented dough and stuffing.During fermentation,steaming,cooling the temperature has significant change and the process is known as 'Thermal history'.The definition of 'Thermal history' is the temperature experirnce from one state to another.In the case of food,it refers to the courses of temperature changes before consumption.The objects of the study are three types of Baozi(Caibao,Roubao,Doushabao).The heat and mass transfer mechanism were investigated.The mechanism about the edible quality changes of Baozi during thermal history were studied.In the study,fermentation process was optimize,a mathematical model of the steaming process and a simulation model of the cooling process were established.The relationship between the moisture content,state,distribution and the texture characteristics were established respectively with NMR(Low Field Magnetic Resonance Imaging)and MRI(Magnetic Resonance Imaging).Edible quality of buns can influence by moisture.A theoretical basis and practical guidance was set up to explain the influence of temperature on the edible quality of Baozi.The main content and results of this paper are as follows:(1)The effect of the fermenting process on the sensory edible quality.In order to confirm the range of fermentation temperature and time of baozi.The temperature changes of various parts of Baozi were recorded by using thermocouple.Then the Box-Behnken response surface method was used to optimize the fermenting process with quality as evaluation index,in order to determine the best conditions.The influence order of each factor on sensory evaluation was:fermentation temperature>fermentation time>yeast addition.The optimum process were as follows:fermentation temperature(B)40.21 0C,fermentation time(A)45.95 min and content of yeast(C)0.49%.The sensory evaluation error was 1.45%between the theoretical value and the predicted value,and the sensory evaluation score equation model is:Y = 83.53 + 1.05A + 1.50B + 0.91C-13.00AB-11.00AC-16.77BC-6.54A2-13.86B2-8.44C2.The degree of fermenting process could be evaluated by the crumb structure image(2)The effect of steaming process on the temperature and steaming characteristic parameters of Baozi,including water absorption,gelatinization degree,soluble protein contentAccompanied with heat and mass transfer in the steaming process,the steaming characteristic parameters of Baozi changed constantly.In different steaming power conditions,a steaming parameters of the dynamic model was built to describe dough and stuffing heat transfer performance.The influence of steaming time and steaming power on the quality of Baozi could be predicted by the correlation analyze of the dough temperature,the RVA value and the steaming parameters.The results showed that the thermal conductivity of the stuffing increased with time goes by,and the thermal conductivity of the dough was decreased with the lapse of time.The steaming process of Baozi was divided into three stages.With the steaming time extended,the steaming parameters of Baozi with different steaming power begin quickly and then slowly.There is a significant correlation from the crumb temperature,RVA value to the steaming parameter value.The maturity could be predicted by the temperature of the crumb.(3)The texture results and moisture content,state,distribution of different stuffing change during cooling process.The results of NMR and MRI showed that the steaming and cooling processes changed the water content and moisture distribution in the Baozi.T2 spectrogram shows that the steaming process makes the water content of Caibao,Roubao,Doushabao A22 increase,and the A23 content reduced.The cooling process makes the water of Caibao,Roubao,Doushabao shift from bound water to free water.MRI showed that with the cooling time increase and the temperature decreased,water in the crumb gradually lost.Part of the moisture in the Cai stuffing is transferred into the crumb and others back to the Cai stuffing.The moisture and fat in the Rou stuffing is transferred to the crumb.The moisture migration in the Dousha stuffing mainly occurs in the upper layer of the crumb.The temperature change is the main cause of this phenomenon.Constant change of the moisture content,state and distribution of Baozi lead the texture characteristics of Baozi change.The temperature and the cooling time of the crumb have a significant correlation with the hardness,stickiness and chewiness.Therefore,with cooling time increase,temperature of Baozi gradually decreased,the content and distribution of the components also change,finally affect the edible quality of Baozi.(4)Build a numerical simulation computer model of cooling process.The thermophysical properties of the stuffing can be estimated by superposition rule.Use software---ANSYS fluent 16.0 to simulate temperature change.Results show that there is no significant difference between the computer model and the actual temperature of Baozi.So the computer simulation model can be used to analyze the temperature of Baozi in the cooling process.This study describe some appearances during 'Thermal history' and explain the reason why edible quality of steamed Baozi change.Provide theoretical basis and practical guidance to optimize the edible quality of Baozi.