Experiment Study On Ice-temperature Vacuum Drying Of Spinach

The research is aimed at experimentally studying drying of leafy vegetables under ice-temperature vacuum condition.The experimental sample is spinach.More specifically,the study is focused on the following objectives:(a)ice-temperature vacuum drying dynamics was studied,and 8 mathematical modeling were tested to select the best model for describing the drying curve equation of spinach during drying.(b)Compared with convective drying and frozen vacuum drying,some qualities,such as rehydration,chlorophyll,color and vitamin C were analyzed.(c)According to some survey data,economic and industrial development prospects for ice-temperature vacuum drying were summarized and forecasted.The results were showed as follows:(1)According to the experimental data under 0?,5? and 10?,drying characteristics of spinach were studied,the results showed that there was no constant drying process during ice-temperature vacuum drying.There was a maximum drying rate during the 1st drying hour.The higher the drying temperature was,the shorter the time was to reach equilibrium moisture content.According to Fick's Second law,the effective diffusion coefficient of spinach was calculated,and the results showed that with the temperature increasing,the effective diffusion coefficient increased.The activation energy was calculated by plotting lnDeff curve,and the value was 32.84 kJ/mol which was within the range of values of actual material.Eight kinds of models were fitted by Matlab,and Two-term model was the best for spinach drying.(2)The rehydration ratio of ice-temperature vacuum drying was 8.0,which was lower than frozen vacuum drying's 9.2,but higher than convective drying's 5.1.Frozen vacuum drying had a advantage on saving the organizational structure of spinach.Spinach dried by frozen vacuum drying was good at porous.Although ice-temperature vacuum drying had a little damage on spinach structure,it still had a good performance on rehydration.Ice-temperature vacuum drying had the same performance with frozen vacuum drying on preserving chlorophyll.Chlorophyll content dried by ice-temperature vacuum was 18.7 mg/g d.b,while the value for frozen vacuum drying and convective drying was 18.7 mg/g d.b.,11.5 mg/g d.b,respectively.On color protection aspect,ice-temperature vacuum drying and frozen vacuum drying had the same effect,and convective drying was not as good as the other two drying methods.Compared with frozen vacuum drying and convective drying,ice-temperature vacuum drying is good at vitamin c(VC)protection.Because VC is a heat-sensitive compound,and if it is long-term in contact with air,it will be easily oxidized.Consequently,convective drying is not as good as ice-temperature vacuum drying at VC protection.(3)Paper was programmed to analyze the ice-temperature drying prospects for industrial development.It was obviously that energy consumed during ice-temperature vacuum drying was not as much as frozen vacuum drying.Consequently,ice-temperature vacuum drying had a large profit margins.With the promotion of ice temperature technology,ice-temperature vacuum drying will have a broad market.