Structural characterisation of two medium molecular mass exopolysaccharides produced by Lactobacillus fermentum Lf2.

AHMED, H.; RANSOM-JONES, E.; SADIQ, S.; VITLIC, A.; MCLAY, N.; ALE, E.; ROJAS, M. F.; BINETTI, A. G.; COLLETT, A.; HUMPREYS, P.; LAWS, A.

CARBOHYDRATE RESEARCH

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2020

0008-6215

Under optimized conditions, the lactic acid bacterium Lactobacillus fermentum Lf2 secretes up38 to 2 gL-1 of a mixture of polysaccharides into the fermentation medium when grown on39 sucrose. Earlier studies had shown that the mixture is biologically active and work was40 undertaken to characterise the polysaccharides. Preparative size exclusion chromatography41 was used to separate a high molecular mass -glucan (weight average mass of 1.23 x 10642 gmol-1) from two medium molecular mass polysaccharides (weight average mass of 8.8 x 10443 gmol-1). Under optimized growth conditions, the medium molecular mass polysaccharides44 accounted for more than 75% of the mixture by weight. Monomer, linkage analysis and NMR45 spectroscopy of the medium molecular mass polysaccharides, and material isolated after their46 Smith degradation, was used to identify the structure of the component polysaccharides. The47 mixture contains two novel polysaccharides. The first has a main chain of -1,6-linked48 galactofuranoses which is non-stoichiometrically 2-O-glucosylated. The degree of substitution49 at the 2-position, with -D-Glcp, depends on the fermentation conditions; under optimized50 conditions greater than 80% 2-O--D-glucosylation was observed.51 6)--D-Galf-(152 253 54 155 -D-Glcp)0.85657 The second polysaccharide is a heteroglycan with four monosaccharides in the repeat unit:58 3)--D-Glcp-(13)--D-Galf-(16)--D-Galf-(159 260 61 162 -D-Glcp6364 Residual signals in the NMR suggest that the sample also contains trace amounts (<3 %) of65 cell wall polysaccharides.66 Keywords: Exopolysaccharide; LAB; Probiotic; Lactobacillus fermentum; NMR