Study On Combined Superheated Steam And Vacuum Drying To Potato

High operation temperature often leads to quality deterioration during the traditional production of potato powder which is also a process of high energy consumption.Superheated steam drying(SSD)is a relatively new food processing technology which has a fast drying rate.It's environmental friendly and save energy also.Vacuum drying(VD)can be operated at low temperature and the rehydration capacity of the products is well.The application of combination of superheated steam drying and vacuum drying(SSVD)into potato powder production may improve the quality attributes and save energy.In this paper,drying characteristics of potato processed by SSD,VD,and SSVD were separately studied.The optimum conditions of potato powder processed by SSVD were investigated.The quality of potato powder processed by four different drying methods(combine superheated steam-vacuum drying,superheated steam drying,vacuum drying,hot air drying)were compared.(1)Drying characteristics of potatoes were studied by SSD method.The effects of steam temperature(105 ??110??115?),potato thickness(1.5 mm?3 mm?4.5 mm)and steam velocity(0.9 m/s?1.2 m/s?1.5 m/s)on drying characteristics were investigated.Meanwhile,we established a model describing potato moisture diffusion during SSD.The simulation results showed that the higher steam temperature was,the more obvious changed in material temperature and shorter in drying time as well as constant drying phase duration.Drying time and dehydration rate of constant-speed phase increased with increasing the thickness of slices.When steam velocity increased,the drying time shortened.However,the effect of steam velocity was not significant,compared with steam temperature and material thickness.The model in partial differential equation form was described(?)m/(?)t = Deff((?)2m/(?x2)+(?)2m/(?)y2),which can be used to predict moisture migration inside the potato during the drying process.(2)The influence of temperature(60 ??70 ??80 ?)and vacuum degree(0.07 MPa?0.08 MPa?0.09 MPa)on drying characteristics of potatoes during VD process was investigated in our study.Besides,during combined drying process,the effects of temperature of SSD and VD respectively and conversion time on characteristics of potatoes were studied,meanwhile,the optimal conditions of preparing potato powder were obtained.The results showed that when temperature was 80 ? during vacuum drying process,drying time was the least.And vacuum had little influence on drying characteristics of potatoes.In this paper,superheated steam drying technology was applied first,then vacuum drying technology.The optimal conditions were:temperature for 105 ? by superheated steam drying,conversion time for 30 min and temperature for 80 ? by vacuum drying.(3)The effects of four different drying methods(hot air drying technology,SSD technology,VD technology and SSVD technology)on potato quality were discussed.Drying time,rehydration ratio,shrinkage rate,color,texture and sensory evaluation value were the indexes.The results demonstrated that the best one in quality was the potato powder by SSVD technology which consumed less energy.Thus,the technology was worthy of promotion in the agricultural product drying process.