Chemical and Rheological Properties of the β-Glucan Produced by Pediococcus parvulus 2.6

Some physicochemical and rheological properties of the exopolysaccharide (EPS) produced by Pediococcus parvulus 2.6 were examined. Structural characterization by NMR (1H and 2D-COSY) showed that the same EPS, a 2-substituted (1,3)-β-d-glucan, was synthesized irrespective of sugar source used for growth (glucose, fructose, or maltose). The molecular masses of these β-glucans were always very high (>106 Da) and influenced by the culture medium or sugar source. The steady shear rheological experiments showed that all concentrations of the β-glucan aqueous solutions exhibited a pseudoplastic behavior at high shear rates. Viscoelastic behavior of β-glucan solutions was determined by dynamic oscillatory analysis. A critical concentration of 0.35% associated with the appearance of entanglements was calculated. The β-glucan adopts an ordered hydrogen bond dependent helical conformation in neutral and slightly alkaline aqueous solutions, which was partly denatured under more alkaline conditions.