Abstract: This study aimed to develop a vacuum freeze drying method for preparing fermented goji berry powder with active Lactobacillus plantarum. Differential scanning calorimetry (DSC) and freeze drying microscopy were used to analyze the physical properties of fermented goji berry pulp. The type and concentration of lyoprotectant were optimized by orthogonal array design, meanwhile, and freeze-drying curves were obtained. By using DSC with continuous scanning after annealing at ?5 ℃ with a heating rate of 5 ℃/min, the physical parameters of the fermented goji berry pulp were determined as follows: co-melting point ?5.28 ℃, eutectic point ?19.59 ℃, glass transition temperature ?31.82 ℃, and disintegration temperature ?36 ℃. On this basis, the pre-freezing temperature was ?40 ℃, pre-freezing time 4 h, and sublimation drying temperature ?45 ℃. The optimal lyoprotectant combination was 20% maltodextrin, 14% lactose and 6% trehalose, and the resulting sublimation drying temperature was ?30 ℃. The viable cell count of the fermented goji berry powder, with good color and rehydration characteristics, was 9.6 (lg (CFU/g)), and the water content was lower than 3%, indicating high quality of the product.

Key words: goji berry powder, high viable count, vacuum freeze drying, lyoprotectant