Evidence of membrane damage in Lactobacillus bulgaricus following freeze drying

The mechanism of inactivation of Lactobacillus bulgaricus due to freeze drying was investigated. Cells were freeze-dried in skim milk powder, maltodextrin, glycerol, trehalose and water. Results are presented confirming previous authors' observations regarding membrane damage during freeze drying. In an attempt to define more clearly the nature of this damage, further experiments were carried out. Results show that following freeze drying changes occur in the unsaturated : saturated fatty acid ratio, a decrease in the activity of the membrane-bound enzyme ATPase and a loss of Delta pH.