Abstract: For long term storage and to improve its stress resistance, Bifidobacterium longum was made into active bacteria powder by vacuum freeze-drying or spray-drying. In this study, we first optimized the technological conditions for active Bifidobacterium longum powder production and then compared these two processes in term of bacterial survival rate, cost, and ease of operation. The viable count, survival rate, moisture and viable count after storage for 90 days at 4 ℃ of vacuum freeze-dried active Bifidobacterium longum powder were 7.98 × 109 CFU/g, 90.9%, 3.8%, and 2.5 × 108 CFU/g, respectively. The powder dissolved easily in water. In contrast, the viable count, survival rate, encapsulation efficiency, moisture and viable count after storage for 90 days at 4 ℃ of spray-dried Bifidobacterium longum powder were 4.4 × 109 CFU/g, 82.2%, 71.9%, 5.6% and 4 × 108 CFU/g, respectively. It took longer time to dissolve in water when compared to vacuum-freeze dried powder. Vacuum freeze-drying was more complicated to operate, time-consuming and expensive than spray-drying. In conclusion, these two processes have both their advantages and disadvantages, which make them fit for different purposes.

Key words: vacuum freeze-drying, spray-drying, Bifidobacterium longum, active bacteria powder, process, comparison