龙眼真空冷冻干燥工艺优化

Optimization of vacuum freeze-drying technologies of longan fruits

为了确定龙眼真空冷冻干燥的工艺参数,以"乌龙岭"龙眼为材料,采用电阻法测量龙眼真空冷冻干燥的物料共晶点和共熔点温度,并应用单因素和正交试验,以冻干品形态保持、色泽、生产能耗等指标进行综合评定考察冻干效果,优化龙眼真空冷冻干燥工艺。结果表明:龙眼真空冷冻干燥物料的共晶点温度和共熔点温度分别为-26.0℃和-20.0℃;优化的技术工艺为龙眼果肉剪半或剪成片形,温度段设定为95℃(7h)→85℃(1h)→75℃(1.5h)→65℃(3h)→55℃(至结束),干燥仓真空值60～70Pa,物料最高温度为50℃。应用该优化的技术工艺可达到最大限度地节省生产能耗,提高冻干品形态保持率的效果,冻干品外观色泽呈白色至微淡黄色。

In order to confirm the optimum technological parameter in vacuum freeze-drying of longan, experiments were conducted with longan cultivar ＂Wulongling＂. The eutectic point and the consolute point of longan were determined by electrical resistance method in the vacuum freeze-drying. The technologies of the vacuum freeze-drying of longan were optimized with both the single-factor and the orthogonal experiments, and according to evaluating the effects of the comprehensive indexes, including shape-keep rate, colors of the products and the energy consumption in the process. The results showed that the eutectic point and the consolute point of longan’s pulp materials were -26℃ and -20.0℃ in the vacuum freeze-drying, respectively. The optimized technology was to cut the longan’s pulp into half or slices,with the temperature phases set as 95℃（7 h）→85℃（1 h）→75℃ （1.5 h）→65℃（3 h）→55℃（to the end）, the vacuum value of drying chamber ranged from 60 Pa to 70 Pa, and the maximum temperature of 50℃. With the optimal technology, the energy consumption could be saved as far as possible,the shape-keep rate of freeze-drying product could be improved, and the product color was maintained from white to light yellow.