The objective of this work was to assess the impact of various NaCl concentrations on Lactobacillus rhamnosus OXY viability after freeze-drying. Osmotic stress was applied during the exponential growth phase of bacterial culture. At salt concentrations between 0.2–0.5 M, a high biomass concentration and a significant increase in cell viability after lyophilisation was observed. An analysis of two-dimensional protein gels indicated the presence of shock proteins, for example, GroEL, ClpB, DnaK, TF, which provide resistance during freeze-drying and subsequent storage. On the basis of these results, it is recommended that lactic acid bacteria cultures be sub-lethally treated with 0.5 M NaCl before freeze-drying.
Authors:M. Polak-Berecka, A. Waśko, H. Skrzypek, and A. Kreft
The ability to produce exocellular polysaccharides is widespread among lactic acid bacteria; however, only some strains produce both capsular polysaccharides (CPS) and exopolysaccharides (EPS). The increasing demand for novel synbiotic products requires a search for new probiotic EPS-producing strains. In this work, we provide evidence that Lactobacillus rhamnosus E/N is capable of producing both forms of polysaccharides when grown in MRS broth. CPS surrounding the bacterial surface was observed by optical microscopy and transmission electron microscopy. EPS present in the growth medium was produced mainly during the exponential growth phase. CPS and EPS were extracted from the culture of Lb. rhamnosus E/N with yields of 12.6 mg l−1 and 146 mg l−1, respectively. It was shown that the method used to isolate the EPS fraction exerted a strong influence on the final amount of EPS obtained. In this study, we propose the most effective method of extraction of EPS from Lb. rhamnosus cultures. Lb. rhamnosus E/N could be considered for potential technological application as a probiotic for use in improving the properties of new pharmaceutical products.