Design And Testing Of Figs Vacuum Pulsating Radio Frequency Blanching And Drying Device

In order to the problems of low heat transfer efficiency,poor enzyme inactivation color protection effect,long drying time,poor quality after drying and low quality retention in current figs blanching and drying technology.The paper combined radio frequency heating technology and vacuum pressure pulsation technology to design and manufacture a figs vacuum pulsation radiofrequency blanching and drying device.And carried out radiofrequency blanching and vacuum pulsation radio-frequency drying tests on the device.The distribution of electric field,temperature and water content of figs was obtained by numerical simulation.The main contents are as follows:The device is mainly composed of radio frequency generation system,upper plate transmission system,working tank,vacuum generation system,and control system.This device can realize figs radio frequency blanching processing and vacuum pulsation radio frequency drying,which has certain advantages for improving figs blanching effect,drying rate and quality.Radio frequency blanching and vacuum pulsation radio frequency drying of figs were carried out.The results showed that slice thickness,blanching target temperature and plate spacing had significant effects on POD and PPO enzyme activities of figs(P < 0.05).Larger slice thickness and target temperature,smaller plate spacing could obtain lower enzyme activities.Compared with hot water blanching,radio frequency blanching had better enzyme inactivation and color protection effects.The optimum conditions of figs radio frequency blanching were unsliced,target temperature of 90 ℃ and plate spacing of 80 mm.Under these conditions,the relative enzyme activities of POD and PPO were 4.77% and 7.56%.Slice thickness,plate spacing,vacuum pressure,vacuum pulsation ratio had significant effects on figs drying rate,total phenol content,color,chewability,adhesion,shrinkage and rehydration ratio(P < 0.05).Vacuum holding time had more obvious effects on drying rate than atmospheric holding time.Compared with hot air drying,vacuum pulsation radio frequency drying time could significantly reduce drying time.The best parameters of figs vacuum pulsation radiofrequency drying test were slice thickness of 3 mm,plate spacing of80 mm,vacuum pressure of 30 k Pa,vacuum pulsation ratio of 20:5 min:min,and the time was 260 min shorter than that of hot air drying.Finite element analysis software COMSOL Multiphysic was used to numerically simulate fig’s electric field and temperature distribution during radio frequency scalding process and fig’s water content distribution during vacuum pulsation radio frequency drying process.The results showed that the size and shape of figs could make radio frequency waves refracted inside the figs,and the electric field intensity was positively correlated with the thickness of figs slices.The electric field intensity in the center was higher than that in the edge,and the heating rate in the center was higher,which resulted in the temperature difference of figs.The electric field intensity was negatively correlated with the distance between plates.Decreasing the distance between plates could increase the temperature rise rate of figs,while increasing the distance between plates could obtain a more uniform temperature distribution.In the radiofrequency drying process of vacuum pulsation,Fig’s water diffused from inside to outside,and the central water content was the lowest after drying.