Effects of annealing on freeze-dried Lactobacillus acidophilus

During a fast freeze, the high viscosity of the trehalose-phosphate solution limits ice crystal formation. Annealing of frozen samples at a temperature above T-g increases ice formation and improves the efficacy of subsequent drying processes. By varying the annealing temperature and time, one can dictate the extent of ice crystal formation and resultant residual moisture content in the freeze-dried product. For Lactobacillus acidophilus, the optimal moisture content of 5 wt% results in 30% recovery after 3 mo of storage at 37 degreesC. The morphology of the freeze-dried product containing 5 wt% moisture showed evidence of localized collapse, but it remains white and readily soluble after storage at 37 degreesC for 3 mo.