engleski

Characterization of exopolysaccharides (EPOLs) produced by probiotic starter culture Lactobacillus fermentum D12

The synthesis of exopolysaccharides (EPOLs), by Lactobacillus fermentum D12, an autochthonous fresh smoked cheese strain, was detected based on the „ropy“ phenotype. Since EPOLs production can be induced by excess of carbohydrates in the culture medium, Lb. fermentum D12 was inoculated in the several media depending of source of carbohydrates used ; glucose, galactose, lactose, fructose and sucrose, at 30°C. The highest yield of the produced EPOLs was achieved when adding a glucose as an induction factor, ranging to the value of 200, 25 mg/L, indicating that Lb. fermentum D12 is highly exopolysaccharide producing strain. The 1H-NMR spectroscopy analysis revealed that the different type of sugars added in the culture medium do not affect the chemical structure of the produced EPOLs. High Performance Size Exclusion Chromatography (HPSEC) of purified and freeze-dried EPOL revealed the presence of the three molecular species ; one with a molecular weight of 400 kDa and two with molecular weight lower than 2 kDa. Next, 1H-NMR, GC and GC-MS analysis showed that Lb. fermentum D12 is a producer of three different types of EPOLs ; one homopolysaccharide and two different heteropolysaccharides. 2D-NMR spectroscopy revealed that the EPOL with the highest molecular mass consists of repeating units of α-1, 4 linked D-glucose, where the 20 % of sugars bear an acetyl substituent on the C-3 position. Future experiments will be directed to establish the primary structure of the lower molecular mass fractions and the potential role of all three isolated EPOLs in the probiotic activity of the Lb. fermentum D12 strain, particularly in adhesion to human intestinal epithelial Caco-2 cell line and in competitive exclusion of pathogens.

xopolysaccharides, homopolysaccharide, heteropolysaccharides, probiotic activity

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