Evaluation of the effect of freeze-drying on potential probiotic properties of different lactic acid bacteria

The potential probiotic properties of different strains of lactic acid bacteria previously isolated from commercial yogurts and from "alheira", a traditional Portuguese fermented dry sausage, have been evaluated during this study. Susceptibility to different antibiotics and the survival under the simulated gastrointestinal conditions, were examined before and after freeze-drying in the presence and in the absence of skim milk 11% (w/v). Lactobacillus plantarum and Pediococcus acidilactici were the most resistant to the adverse conditions of the gastrointestinal tract and to the antibiotics tested. All the isolates were demonstrated to be vancomycin resistant. In general, antibiotic resistance decreased after freeze-drying. Resistance to gastrointestinal conditions decreased after freeze-drying in the absence of skim milk, which might be explained by the protective effect of the drying medium. Only P. acidilactici isolates were demonstrated to have antimicrobial activity against the tested Listeria monocytogenes strains, which was also retained after freeze-drying.