Ultrasonic Vacuum Drying And Its Application

Ultrasound has been widely used in food industry as pretreatment of hot-air drying,osmotic dehydration,vacuum drying and so on.Vacuum drying creates an environmental pressure that is much less than the atmospheric pressure and therefore evaporates water at low temperatures,which is suitable for foods that contain thermolabile substances.To shorten the drying period and to improve the quality of dried foods,a novel ultrasonic vacuum drying(UVD)equipment was designed and assembled.For drying carrots,maca,Cistancle deserticola and Lycium barbarum polysaccharide(LBP),the efficiency and product quality of UVD was evaluated and compared with other drying techniques.This work laid the basis for industrial application of ultrasonic vacuum drying.(1)UVD can promote water transfer and improve drying quality of carrot slices.Carrot slices were dried with hot-air drying(OD),vacuum drying(VD)and UVD(300/500/700 W).The UVD technique had the highest effective diffusion coefficient(Deff)value of 8.58×10-10 m2/s,followed by VD of 3.96×10-10 m2/s and OD of 8.07×10-10 m2/s.The Midilli et al.model fitted the drying curves of carrot slices.The response surface design was used to optimize the ultrasonic vacuum drying process of carrot.The optimum drying condition was ultrasonic power of 500 W,vacuum of 99.89 kPa,drying temperature of 23.73?.The research of the changes of interval water in carrot by using low field nuclear magnetic resonance(LF-NMR).Free water obviously decreased in the first 20 minutes during the process of UVD.Followed 40 minutes were mainly for the removal of bound water.Carrot slices with UVD showed the best color and the smallest deformation.The larger the ultrasonic power,the more of micro-channels and larger cavities.UVD showed the fastest rehydration rate and the highest rehydration ratio when compared to OD and VD.The ?-carotene content of dried carrot slices were OD(81.59 mg/100 g)<VD(114.18 mg/100 g)and UVD of 300 W(122.20 mg/100 g)<UVD of 500 W(164.79 mg/100 g)and UVD of 700 W(162.58 mg/100 g).(2)UVD can promote water transfer of maca slices and synthesis of macamides.The research of UVD on maca slices was similar to the research of carrot.Within the range of ultrasonic power of 0-700 W,the larger the ultrasonic power,the more and larger of micro-channels and the higher of rehydration ratio.Macamides contents in maca slices by different drying methods were UVD of 700 W(62.89 ?g/g DM)<0 W(64.10 ?g/g DM)<300 W of UVD(128.58 ?g/g DM)<500 W of UVD(189.52 ?g/g DM).After 15 weeks,macamides contents in maca slices by different drying methods were 0 W(244.06 ?g/g DM)<UVD of 300 W(372.34 ?g/g DM)<UVD of 700 W(412.05 ?g/g DM)<UVD of 500W(422.49 ?g/g DM)?(3)Increase of drying temperature could promote UVD of Cistanche deserticola.The effect of drying temperature on UVD of Cistanche deserticola were studied.Drying conditions were ultrasonic power 700 W,vacuum degree 100 kPa,drying temperature 20/30/40?.The Midilli et al.model fitted the drying curves of Cistanche deserticola slices.The effective diffusion coefficients of Cistanche deserticola slices were 2.66 m2/s at 20?,3.24 m2/s at 30?,3.65 m2/s at 40?.Increasing drying temperature could promote the drying process of Cistanche deserticola.Dried Cistanche deserticola of UVD showed the least amount of echinacoside and acteoside.(4)UVD could shorten the drying time of Lycium barbarum polysaccharide(LBP).The drying time of UVD was shorter than OD and longer than freeze drying(FD).LBP dried by UVD had fine color,loose texture and less damage of polysccharide.While FD is not suitable for industrial production due to its high cost and limited scale.