To optimize the technology of on-line detection technology and automatic control system,the fresh turnip harvested in this year as test material,by analyzing the results of single factor experiment,heating temperature(60-80℃),vacuum in the warehouse(3 000-4 000 Pa),and material thickness(4-10 mm)were used as main test factors.Taking dehydration rate,rehydration rate,and VC mass ratio of dried product as test indexes,and using the quadratic general rotary unitized design approach,the influence and change law of far-infrared vacuum drying on drying turnip was studied.Analysis of interaction effects between the factors and the regression model,the regression equation was established,and the objective function optimization,the integrated balance method were adopted to identify the optimal conditions:the vacuum was 3000 Pa,the heating temperature was 70℃,and the material thickness was 7 mm.Under these conditions,the dehydration rate of dried turnip products was 25.23 g/(m2·h),VC mass ratio was2.05 mg/g,and the optimal value of rehydration ratio was 3.95.Finally,the turnip dry products were observed by SESM and the results were analyzed.The result showed that the cell wall breakage rate,cell deformation rate,and low profile shrinkage rate of turnip dried by infrared vacuum were lower;the surface smoothness preservation rate was higher;the cell tissue preservation rate was more than 80%,and the cell breakage and distortion was less.And the microscopic morphology of cell was kept well.Under these conditions,the original organization and structure of the sample were truly reflected,the better drying effect was achieved,the sensory quality of dried products was guaranteed.This study provide a technical basis for the intelligent far-infrared vacuum drying technology applying for fast drying of high moisture materials and a reference for improving the quality of the far-infrared vacuum drying of turnip.
