Use of conductimetry to evaluate Lactobacillus delbrueckii ssp. bulgaricussubjected to freeze-drying

The survival rate of Lactobacillus delbrueckii ssp. bulgaricus and the lact ic acid production in milk after freeze-drying was evaluated by viability a nd conductimetric assays. Most strains showed a typical conductance before freeze-drying which became flat after the process. Differences in Detection Time (DT) before and after lyophilization (expressed as Delta DT) were in the range of 0.8-19.8 according to the suspension medium and the strain und er study. Both the survival rate and the acidifying capacity of the culture s were better preserved when sodium glutamate (as cryoprotector) was added to skimmed milk.