Drying characteristics and its effects on quality of jujube treated by combined microwave-hot-air drying

To improve the quality of dehydrated Chinese jujube, the combined methods of microwave drying, hot-air high temperature drying and hot-air low temperature drying were utilized to dry Chinese jujube on the basis of segmented hot-air drying method and intermittent microwave drying method. Theeffects of different drying methods on drying characteristics and quality of jujube were studied. The results showed that the drying time of the combined methods were shortened more than 11% compared with segmented hot-air drying method.The internal temperature of jujube dried by segmented hot-air drying method was higher than the surface temperature. The temperature of jujube was highly increased using intermittent microwave drying method, resulting in high drying rates. The optimal parameters were 300g jujube dried for 12 min at 119 W of microwave, paused for 4 min, repeated times of 7, hot-air drying time of 9h at 55℃ and hot-air drying time of 12h at 50℃. Under the optimal conditions the Vitamin C content of jujube was the highest, the browning degree was quite low, the effect of rehydration was very well, and the energy consumption was quite low.Therefore, it was a good method that microwave drying followed by hot-air drying, and it was quite suitable for drying Chinese jujube.