Resistance of functional Lactobacillus plantarum strains against food stress conditions

• Resistance to thermal, oxidative and osmotic stress of three potential probiotic Lactobacillus plantarum strains was studied.
• Thermal adaptation was also assayed.
• Different responses among the strains were obtained.
• The strains improved their thermal and osmotic resistance with thermal adaptation.
• One strain with higher general resistance against the studied stress factors was selected.

The survival of three Lactobacillus plantarum strains (Lp 790, Lp 813 and Lp 998) with functional properties was studied taking into account their resistance to thermal, osmotic and oxidative stress factors. Stress treatments applied were: 52 °C–15 min (Phosphate Buffer pH 7, thermal shock), H2O2 0.1% (p/v) – 30 min (oxidative shock) and NaCl aqueous solution at 17, 25 and 30% (p/v) (room temperature – 1 h, osmotic shock). The osmotic stress was also evaluated on cell growth in MRS broth added of 2, 4, 6, 8 and 10% (p/v) of NaCl, during 20 h at 30 °C. The cell thermal adaptation was performed in MRS broth, selecting 45 °C for 30 min as final conditions for all strains. Two strains (Lp 813 and Lp 998) showed, in general, similar behaviour against the three stress factors, being clearly more resistant than Lp 790. An evident difference in growth kinetics in presence of NaCl was observed between Lp 998 and Lp 813, Lp998 showing a higher optical density (OD570nm) than Lp 813 at the end of the assay. Selected thermal adaptation improved by 2 log orders the thermal resistance of both strains, but cell growth in presence of NaCl was enhanced only in Lp 813. Oxidative resistance was not affected with this thermal pre-treatment. These results demonstrate the relevance of cell technological resistance when selecting presumptive “probiotic” cultures, since different stress factors might considerably affect viability or/and performance of the strains. The incidence of stress conditions on functional properties of the strains used in this work are currently under research in our group.