Combined Vacuum Microwave-vacuum Freeze Drying Of Carrot

It is studied the combined vacuum microwave-vacuum freeze drying of carrot, including the conversion point in combined drying,the conditions of vacuum microwave drying in combined vacuum microwave-vacuum freeze drying of carrot on conversion point and constant drying rate,and the influence of the combined drying conditions on quality of carrot.The selection of conversion point of combined drying was explored by the change of V_C content in vacuum microwave drying.And the critical water content was identified as turning point shift from vacuum microwave drying to vacuum freeze-drying.We also explored the conditions of vacuum microwave drying on critical water.It showed that the increase in microwave power can speed up the arrival time of critical water points,and does not affect the critical moisture content;the increase in load to extend the arrival time of critical water points,while also reduce the critical moisture content;when slice thickness in 4-7mm,the arrival time of critical water points were 12.5min,and the critical water content were 3 kg/kg,and when slice thickness at 8-9mm,the arrival time of critical water point were 10min, and the critical water content were 3.5kg/kg..By studied the conditions of vacuum microwave drying in orthogonal experiment, it found that the energy consumption of combined drying,the hardness and resilience of dried carrot were not significant influence by microwave,loading,slice thickness and vacuum,but the rehydration ratio was significant influenced by microwave, loading,slice thickness had significant on,but not significant influenced by vacuum. By the analysis of variance and range,It showed the optimum conditions on rehydration rate were microwave power in 500W,loading in 100g,slice thinkness in 5mm,vacuum degree in 0.09MPa,and the rehydration ratio was 4.17%under this conditions.But in practical operation,the best conditions of vucuum microwave drying were microwave power in 400W,loading in 120g,vacuum degree in 0.08MPa, and the selection of slice thickness was follow quality of dryed materials,and in these conditions,the removed water of vacuum microwave is about 63%-68%.Using uniform test conditions on the vacuum freeze-drying studies,and regression model building,the results showed slice thickness a（mm） inversely proportional to hardness and rehydration rate,but proportional to energy consumption, and shear stress;The heating plate temperature b（℃） proportional to hardness and shear stress,but inversely proportional to energy consumption;The stress of freeze-drying c（mbar） proportion to energy consumption and hardness,but inversely proportion to shear force.Three factors on the impact of energy consumption are highly significant.And the regression equations as follow:energy consumption y₁（KJ/g）=360.283+271.039a-34.977b+765.314c;rehydration y₂（g/g）=4.669-0.273a;harsness y₃（N）=-7.156-0.330a+0.531b+13.553c;shear stess y₄（N）=-0.168+11.284a+0.057b-0.937c.The mathematic model of vacuum microwave drying was established,and when MR≥0.20:MR=exp[-(0.063+8.294×10^-5Q-7.531×10^-4M+2.209×10^-3σ+0.213P_w)t⁽(0.395+4.4×10^-4Q-2.830×10^-3M-0.0192σ+5.962P_w))...