This paper describes the structural elucidation of Leuconostoc mesenteroides P35 exopolysaccharide (EPS-LM). Ln. mesenteroides P35 strain was isolated from a French goat cheese for its capacity to produce EPS increasing the viscosity of a whey-based fermentation medium. The chemical structure of EPS-LM analysis was elucidated by determination of optical rotation degree, macromolecular characterization, sugar units and methylation analyses, FT-IR, 1D NMR spectroscopy (1H and 13C NMR), 2D NMR spectroscopy (1H1H COSY, HSQC and HMBC). EPS-LM was a high molecular weight (ranging from 6.7 × 106 Da to 9.9 × 106 Da) dextran that is composed of only d-glucose units containing α (1 → 6) linkages and paltry α (1 → 3) branches. Since polysaccharide-protein interactions can be exploited to control and design food matrices, EPS-LM interactions with bovine serum albumin (the main constituent of bovine plasma) were investigated by surface plasmon resonance (SPR). Kinetic properties of EPS-LM binding with immobilized BSA via showed an increase of EPS-LM affinity (equilibrium constant (Kd)) for BSA from (2.50 ± 0.01) × 10-5 M-1 at 298 K to (9.21 ± 0.05) × 10-6 M-1 at to 310 K. The thermodynamic parameters revealed that van der Waals and hydrogen binding forces play a major role in the interaction of EPS-LM with BSA. However, EPS-LM-BSA interaction was non-spontaneous, entropy driven and an EPS-LM - BSA binding process was endothermic (ΔG > 0). The structural findings suggested that Ln. mesenteroides P35 α-D-glucan might find widespread technological applications in the biopolymer, medical and food industries.
Keywords: Bovine serum albumin; Interaction; Ln. mesentroides dextran; NMR; Surface plasmon resonance.
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