Production and structural characterization of exopolysaccharides from newly isolated probiotic lactic acid bacteria

In this work, four exopolysaccharide-producing lactic acid bacteria (LAB) strains, newly isolated from Tunisian spontaneously fermented foods and beverages, namely bovine and turkey meat sausages (BMS and TMS), date palm sap (DPS) and cow milk (CM), were identified as Leuconostoc citreum-BMS, Leuconostoc mesenteroides-TMS, Pediococcus pentosaceus-DPS and Leuconostoc pseudomesenteroides-CM, respectively. The isolated strains showed the ability to withstand simulated human gastrointestinal (GI) tract conditions (low pH, lysozyme, bile salts, pepsin and pancreatin) and showed high surface hydrophobicity (79-90%), besides their ability to act against Escherichia coli and Listeria monocytogenes and to produce exopolysaccharides (EPS). Therefore, these isolates can be served as potential probiotics. The produced EPS were growth-associated suggesting that they are primary metabolites. The molecular weights were higher than 106 Da using HPLC-SEC. 2D-NMR results indicated that all the samples were mixtures of dextran and levan, except for EPS-CM which was a levan-type EPS. Furthermore, the EPS samples showed an abitlity to inhibit and to disrupt pathogenic biofilms and showed high thermostability studied via differential scanning calorimetry (DSC) with melting points higher than 224 °C making them promising to be used in thermal processed foods.