Experimental Study On Drying Process Of Vacuum Freezing And Hent Pump-microwave

The article takes Chlamys, Litchi and Tilapia as the raw materials and carried on the process characteristic research of Vacuum freeze-drying and heat pump– microwave drying.This article takes adductor muscle of Chlamys farreri as experimental materials and uses two time poikilothermia and a live pressure process parameter adjustment law in the freezing and drying process. The result shows: material center temperature is influential to the freezing and drying sample's rehydratation rate and the energy consumption when the temperature is changed at the first time. If the first temperature adjustment is carried on when the material center temperature is 1℃, the sample rehydratation rate and the rehydratation speed is quickest, the quality is best, and the dry energy consumption is also at least . On the basis of single-factor test ,through five factors four levels orthogonal tests, the study shows the primary and secondary relations of various process parameters affecting freezing and drying energy consumption and the product quality are: The first high temperature of hot plate>the second high temperature of hot plate> the low pressure of drying chamber> the low temperature of hot plate> the high pressure of drying chamber and the best combination of factors is C4E1B3D3A1, that is The first high temperature of hot plate is 33℃, the second high temperature of hot plate is 39℃, the low pressure of drying chamber is 40 Pa, the low temperature of hot plate is 36℃, the high pressure of drying chamber is 60 Pa.The experiment of drying Litchi was done in a heat pump dryer with multi-function variable conditions. Some of factors, including blanching time and content of healthful color-fixatives such as citrate acid, L-Cys as well as Vc, on the effect of color retention evaluated by a index of integrated sensory quality analysis were invested by single factors and then the color retention technology of dried litchi optimized by an orthogonal experiment of L9(34). The results showed that the taste, flavor and color of dried litchi were influenced significantly by blanching time and different agents of color retention. The order of effects of four factors were: blanching time> content of L-Cys> content of citrate acid> content of Vc. The technological parameters of color retention optimized by orthogonal test were as follow: 160s of blanching time, 0.2% of L-Cys, 0.5% of citrate acid and 0.1% of Vc. Under the optimized conditions, the evaluation index is 23.5.The article takes Litchi as the raw material and carried on the research of the heat pump-microwave combined drying. First,the experiment of drying Litchi was done with heat pump drying device, from the experiment, we obtained the drying curves and drying speed curves of litchi in steady condition, and ascertained the moisture content inversion point of the combined heat pump and microwave drying from the curves. From the orthogonal experiment with three factors and three levels, the index of sensory comprehensive assessment as evaluation standards. We investigated the influence of the heat pump drying temperature,the moisture content of the inversion point of the co-drying ,and microwave drying time on quality of litchi by combined drying. The results showed : the heat pump drying temperature is a major factor in the quality of dried litchi, the influence of the moisture content of the co-drying is greater than microwave drying time. From that , we obtained the combination parameter which made the best quality of dried litchi in the experimental condition is: heat pump drying temperature is 50℃; the moisture content of the inversion point of the co- drying is 1.0; microwave drying time is 2.5min. In the condition of this combination parameter, the score sensory comprehensive assessment is 27.The article takes Tilapia fillets as the raw material and carried on the research of the heat pump-microwave combined drying. Through the single factor experiments , we know that the microwave power was greater, the drying rate was quicker, excessive power caused poor quality of dry products in the process of the heat pump dried Tilapia fillets first to water content of 40% and changed into microwave drying, It proved that a drying time of Tilapia fillets is not appropriate if it is too long in the process of drying and can lead to poor quality of dry products after the different time section's comparison tests of microwave drying, if a drying time is short, the product quality will enhance correspondingly.Through the trial test of the heat pump drying Tilapia fillets, the study shows the wind speed of the heat pump has certain influence to the drying time and the quality that is the greater the wind speed is, the faster the drying rate is, but as the wind speed increases, the influence of the wind speed to drying rate is small and drying rate also drops along with it. Therefore, in the heat pump drying process, it is quite reasonable to use the microwave drying during the dry later period.Tilapia fillets were chosen as the experiment materials. A three-factor, three-level combined experimental design, was chosen to evaluate dependent variables affecting energy consumption, rehydration rate, the temperature of heat pump ,anti-moisture and sensory evaluation by Response Surface Methodology(RSM).The drying process parameters were optimized and obtained.