Freeze-thaw pretreatment improves the vacuum freeze-drying efficiency and storage stability of goji berry (Lycium barbarum. L.)

In order to improve the efficiency of vacuum freeze-drying of goji berry, the effects of multiple freeze-thaw pretreatments (FT) on the water distribution, microstructure, drying characteristics and physicochemical properties of the goji berry were studied. FT effectively shortened the vacuum freeze-drying duration by 4-6 h and reduced the energy consumption by 10.0-15.1 g/100 g compared with the traditional alkaline-dewaxing method. Further analysis revealed that FT accelerated the whole drying process, especially the rapid drying stage, due to the decrease in the bound water. In addition, FT effectively preserved the physicochemical properties, including shrinkage and hardness of goji berries after freeze-drying treatment. In particular, the deterioration of carotenoid-based red color was alleviated after 6 months of storage of freeze-dried goji berry, during which the degradation of carotenoids was significantly inhibited. Comprehensive analysis established that two freeze-thaw cycles are more suitable for the production of dried berries in practice.