Optimization of Hot Air-vacuum Segment-combined Drying Process of Jishan Jujube by Response Surface Method

In order to study the effect of segment-combined drying on the characteristics and quality of Jishan jujube,and optimize the drying process,the hot air temperature,the switching point,vacuum temperature were used as the experimental factors to study the typical quality parameters(V_C content,total sugar content,color,total amino acids)and the drying efficiency(drying time and energy consumption). Then the response surface process was optimized to obtain the best drying method of hot air-vacuum segment-combined drying. The results were as follows:The best drying temperature of hot air drying stage was 64.50℃,and the best switching point was 52.50%,and the best vacuum drying temperature was 65.00℃. Under these conditions,the V_C of dried Jishan jujube retained 26.89% and the total sugar content was 85.21%. The drying time was 23 h,which was 20.68% less than that of single hot air drying(29.00 h). Compared with single vacuum drying(25.00 h),the drying time reduced by about 10%. The energy consumption was 2.45 kW·h,higher than the single vacuum drying(1.48 kW·h),but only 40% of single hot air drying(6.01 kW·h).