葡萄的真空冷冻干燥工艺研究

Study on Vacuum Freeze-drying Process of Grape

探讨了葡萄的真空冷冻干燥工艺,通过低温显微系统观测出在慢速降温时共晶点温度为-15.5℃,对不同前处理(完整,切半,扎针,去皮)的葡萄进行冷冻干燥,干燥工艺为预冻温度-35℃,2h,一次干燥温度-20℃,压强<100Pa,12h,二次干燥温度55℃,压强<100Pa,6h,结果表明:去皮的葡萄冻干效果最好,其失水率可以达到72.93%。将其和50℃热风干燥制备的葡萄干对比,表明真空冷冻干燥的葡萄干在孔隙率和感官等方面均优于热风干燥的葡萄干,因此冷冻干燥工艺是一种较理想的葡萄加工方法。

The paper deals with vacuum freeze-drying of raisin. It was observed by cryo-microscope that eutectic temperature is at-15.5℃ during slow cooling. Pre-treated grapes（intact, half cut, needle punctured and peeled）were freeze-dried at a pre-freezing temperature of-35℃ for 2h, at the first drying temperature of-20℃ and with a pressure lower than 100 Pa for 12 h, at the second drying temperature of 55℃ and with a pressure lower than100 Pa for 6h. It turned out that the freeze-drying effect of peeled grapes demonstrated most satisfactory, whose water loss could reach 72.93%. Compared with raisins prepared by hot-wind drying at 50℃, raisins prepared by vacuum freeze-drying is superior in porosity and appearance. It is concluded that vacuum freeze-drying is a relatively ideal method of processing grapes.