Chemical characterization of the exopolysacharide produced by Lactobacillus plantarum isolated from kefir

GANGOITI V; MEDRANO M.; ABRAHAM A G; HAMET F; PERUZZO JP; DUEÑAS M T; PUERTAS A; PRIETO A

TTucumán

Simposio; SIBAL 2016 - V Simposio Internacional de Bacterias Lácticas.; 2016

CERELA

Exopolysaccharides (EPS) synthesized by lactic acid bacteria (LAB) represent one of the most important natural additives in food industry due to the ability of LAB to produce EPS in situ. Lactobacillus plantarum CIDCA 8327 strain isolated from kefir, previously demonstrated to have high resistance to bile salts, high survival after 1 hour pH 2.5, adhesion to intestinal cells and inhibitory activity against intestinal pathogens is also able to produce B2 vitamin and EPS. The aim of the present study was to characterize the structure of the EPS synthesized by L. plantarum. The strain was grown in sterile milk under aerobic conditions at 30°C for 96 hrs and the EPS was isolated by ethanol precipitation and dialysis against distilled water. Molecular mass was determined by gel filtration (PL Aquagel OH MIXED-H column) in a HPLC system with refractive index detection. Fourier-transformed Infrared Spectroscopy (FTIR) was performed using a Bruker ALPHA-P FT-IR spectrometer (Bruker) with a diamond ATR. NMR spectra were determined at 60°C using a Bruker AMX500 spectrometer operating at 500 MHz (1H-nuclear magnetic resonance). Monosaccharide composition was determined by gas chromatography (GC) after hydrolysis, glycosidic linkages were determined by methylation, hydrolysis and analysis of the partially methylated alditol acetates obtained. Gas chromatography-mass spectrophotometry (GLC-MS) analysis was performed in a Agilent 7890A/5975C instrument. L. plantarum produced 160 mg/L of EPS with a molecular mass of 104 Da. Monosaccharide composition analysis demonstrated that the EPS was composed by glucose (100%). The FTIR spectrum showed typical polysaccharide signals, and all the vibrational peaks were similar to those obtained for glucans. The bands at 1155, 1022, 930, 850 and 760 cm-1 evidenced the presence of a polysaccharide with α-linkages in the structure. The 1H-NMR spectrum showed resonances of hydrogen corresponding to the glucosyl residue. Signals in the region between 5.3 and 4.5 ppm related to the H1-4 and H1-3 are well resolved and indicate α-D-glucans. Both by 1H-NMR and methylation analysis it was possible to estimate that this polysaccharide consists of 80% of linear α-(1→4)-D-glucopyranosyl units, and 19% of the units branched at positions O-3 by single α-D-glucopyranosil units.