Abstract:

In order to confirm the key technology in vacuum freeze-drying of litch, experiments were conducted with litch cultivar ‘Wuye’. The eutectic point and the consolute point of litch were determined by electrical resistance method in the vacuum freeze-drying. The different color fixative agents were compared on their color-protecting effects by analysis the color of the freeze-drying products. The key technical parameters of the vacuum freeze-drying of litch were optimized with the freeze-drying effects of the comprehensive indexes being evaluated by energy consumption, freeze-drying time, appearances shape and colors of the products during the process of vacuum freeze-drying. The results showed that the eutectic point and the consolute point of lithc’s pulp materials were -26℃ and -20.0℃ in the vacuum freeze-drying, respectively. In the solution of 0.6% citric acid or 0.4% citric acid + 0.2%VC with immersing time for 20 min were gaven the best color-protecting effects. At the condition of first drying temperature under 80℃, material maximum temperature of 50℃during sublimation stage, and the combination of the vacuum value in drying chamber ranged from 60 Pa to 70 Pa/from 60 Pa to 70 Pa, could save the energy consumption, shorten the freeze-drying time and improved the appearances shape and color of the vacuum freeze-drying products.