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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.
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.
The central composite design was developed to search for an optimal medium for the growth of Lactobacillus rhamnosus OXY. The effect of various media components, such as carbon sources, simple and complex nitrogen sources, mineral agents, and growth factors (vitamins B, amino acids) was examined. The first-order model based on Plackett-Burman design showed that glucose, sodium pyruvate, meat extract and mineral salts significantly influenced the growth of the examined bacteria. The second-order polynomial regression confirmed that maximum biomass production could be achieved by the combination of glucose (12.38 g/l), sodium pyruvate (3.15 g/l), meat extract (4.08 g/l), potassium phosphate (1.46 g/l), sodium acetate (3.65 g/l) and ammonium citrate (1.46 g/l).The validation of the predicted model carried out in bioreactor conditions confirmed the usefulness of the new medium for the culture of L. rhamnosus OXY in large scale. The optimal medium makes the culture of the probiotic bacterium L. rhamnosus OXY more cost effective.