Growth/Survival of Some Functional Lactic Acid Bacteria Under Different Stress Conditions

Lactic acid bacteria (LAB) used as starter cultures in food industry must survive under several stress conditions, including low pH, low water activity, high and low temperatures, oxidative stress, starvation and competition with other species. Also, a high resistance to low pH values and in the presence of bile salts is necessary for probiotic strains, in order to survive in the stomach and intestine, or even to compete with other bacterial groups in this environment and to colonize the gastrointestinal tract (GIT) of the host. The purpose of the present work was to evaluate the growth/survival of 19 LAB strains with biotechnological applications (production of bacteriocins, exopolysaccharides, S-layer proteins) under different stress conditions. The strains were investigated for tolerance to acidity (pH 2.0, 3.5, 4.5 and 5.5), bile salts (0.05%, 0.1%, 0.2%, 0.3% and 0.5%), different temperatures (15°C, 20°C, 28°C, 37°C, 42°C, 47°C, and 50°C), and different concentrations of NaCl (1%, 3%, 5%, and 7%). All 19 tested strains grew well at 28°C and 37°C, with a viability between 10¹⁰-10¹⁴ CFU/ml. Three strains grew well at 50°C reaching a viability of 10⁸-10⁹ CFU/ml. Four strains were resistant to pH 3.5 and 4.5, after 24 h of incubation reaching a viability of 10¹⁰ CFU/ml and 10¹⁴ CFU/ml, respectively. After 3 h of exposure to pH 2.0, two strains, namely Lb. brevis FV403 and Lb. brevis FV530, maintained a viability of 10²-10³ CFU/ml. Concerning the bile salt resistance, all tested strains showed a high resistance to a concentration of 0.3% (w/v), reaching a cell viability of 10⁷-10⁹ CFU/ml after 24 h of incubation. After 3 h of exposure to 0.5% (w/v) of bile salts, the viability of Lb. brevis FV530 was about 10¹⁰ CFU/ml. Six of the selected strains had a high resistance to NaCl (up to 7%) reaching a viability of 10⁹ CFU/ml after 48 h of incubation.