β-(1 → 3)(1 → 6)glucan from Schizophyllum commune 227E.32: High yield production via glucose/xylose co-metabolization

Abstract

A co-metabolization of xylose and glucose by Schizophyllum commune 227E.32 wild mushroom for exopolysaccharide (EPS) production is presented. Cultivations performed with S. commune 227E.32 at different xylose concentrations demonstrated that the concentration of 50 g·L^-1 of xylose achieved the highest EPS production, around 4.46 g·L^-1. Scale-up in a stirred tank reactor (STR) was performed. 10 % inoculum showed the highest cost/benefit ratio regarding sugar conversion and EPS production (Y _P/S = 0.90 g·g^-1), achieving 1.82 g·L^-1 of EPS. Isolation, purification, and characterization were conducted with EPS produced in flasks and STR. GC-MS analysis showed glucose as main monosaccharide constituents for both isolates. ¹³C NMR and HSQC-edited showed that both EPS isolated consisted of a β-D-Glcp (1 → 3) main chain, partially substituted at O-6 with nonreducing β-D-Glcp ends on every third residue, similar to β-D-glucan isolated from S. commune basidiomes known as schizophyllan (SPG). The M_w was determined by GPC to 1.5 × 10⁶ Da (flasks) and 1.1 × 10⁶ Da (STR). AFM topographs revealed a semi-flexible appearance of the β-D-glucan, consistent with the triple helical structures adopted by SPG and overall contour length consistent with a high molar mass.

Keywords: Mushroom β-(1 → 6)(1 → 3)glucan; Physicochemical characterization; Xylose/glucose co-metabolization.