Structural studies of the exopolysaccharide from Lactobacillus plantarum C88 using NMR spectroscopy and the program CASPER

• The absolute configuration of d-Glc and d-Gal was determined by NMR spectroscopy.
• The program CASPER identified the correct structure in ∼3 min using NMR data.
• Very good agreements were found between CASPER predicted and experimental NMR data.

Some lactic acid bacteria, such as those of the Lactobacillus genus, have the ability to produce exopolysaccharides (EPSs) that confer favorable physicochemical properties to food and/or beneficial physiological effects on human health. In particular, the EPS of Lactobacillus plantarum C88 has recently demonstrated in vitro antioxidant activity and, herein, its structure has been investigated using NMR spectroscopy and the computer program CASPER (Computer Assisted Spectrum Evaluation of Regular polysaccharides). The pentasaccharide repeating unit of the O-deacetylated EPS consists of a trisaccharide backbone, →4)-α-d-Galp-(1→2)-α-d-Glcp-(1→3)-β-d-Glcp-(1→, with terminal d-Glc and d-Gal residues (1.0 and 0.8 equiv per repeating unit, respectively) extending from O3 and O6, respectively, of the →4)-α-d-Galp-(1→ residue. In the native EPS an O-acetyl group is present, 0.85 equiv per repeating unit, at O2 of the α-linked galactose residue; thus the repeating unit of the EPS has the following structure: →4)[β-d-Glcp-(1→3)][β-d-Galp-(1→6)]α-d-Galp2Ac-(1→2)-α-d-Glcp-(1→3)-β-d-Glcp-(1→. These structural features, and the chain length (∼103 repeating units on average, determined in a previous study), are expected to play an important role in defining the physicochemical properties of the polymer.

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