红枣微波-热风联合干燥特性及对其品质的影响

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

为了提高红枣干制品的品质,在分段热风干燥和微波间歇干燥的基础上,采用微波+高温热风+低温热风的联合干燥方式干燥红枣,研究不同干燥方式下红枣的干燥特性和品质。结果表明:联合干燥方式的干燥时间比分段热风干燥缩短11%以上;分段热风干燥的红枣内部温度高于表面温度,微波间歇干燥的红枣温度升高幅度大,干燥速率高。300g红枣在119W下微波干燥12min,间歇4min,重复7次(转换点干基含水率≤99%),然后55℃热风干燥9h(转换点干基含水率≤66%),最终50℃热风干燥12h(干燥方式Ⅳ)的条件下干燥的红枣总维生素C含量最高,褐变系数相对较低,复水效果最好,能耗较低,是较优的红枣微波-热风联合干燥组合。微波-热风联合干燥是适合红枣干燥的较好技术方法。

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.