*2.6. Analysis of Survival Rates Following Freeze-Drying*

The co-culture and mono-culture samples were generated as described above. Afterward, the samples were harvested by centrifugation at 4000× *g* for 10 min. One milliliter of each sample was washed and resuspended with DW; the suspensions were then mixed with an equal volume of skim milk (10%), to optimize the cell viability [34]. The samples were placed in a −80 ◦C freezer for 48 h and subsequently freeze-dried in lyophilizer (Ilshin, Hialeah, FL, USA) for 24 h. The survival rates following the freeze-drying are expressed as the number of CFUs/mL. The cell survivability (following freeze-drying) was studied during incubation of the samples in pH 2 (with 1 M hydrochloric acid) at 37 ◦C, for either 1 h or 3 h, using the CFU counts.
