Optimization and scaling up of extracellular polysaccharide production by submerged culture of Ganoderma lucidum on starch-containing medium using response surface methodology and laboratory bioreactors of various designs.

Abstract

Basidiomycetes, known for their production of bioactive compounds, traditionally use simple sugars for fermentation. However, their ability to degrade complex plant polysaccharides through enzyme secretion presents potential for the use of renewable raw materials. This study focused on the optimization of exopolysaccharide (EPS) production and efficient substrate consumption by Ganoderma lucidum using response surface methodology (RSM). Using an optimized medium containing 15 g⋅l-1 wheat starch, 0.375 g⋅l-1 NH4Cl, and 0.75 g⋅l-1 CaCl2 (C/N ratio of 40), a significant increase in EPS concentration from 121.1 ± 10.2 mg⋅l-1 to 229.0 ± 20.3 mg⋅l-1 and starch degradation degree (SDD) from 9.1% to 57.6% was achieved after 9 d of submerged cultivation. Scale-up experiments were conducted in both column and stirred tank bioreactors, employing submerged and immobilized cultivation modes. Submerged cultivation in the column bioreactor yielded the highest process desirability of 0.56, achieving EPS concentration of 192.5 ± 5.4 mg⋅l-1 and 60.2% SDD within 7 d. These results highlight the potential of the used column bioreactor for efficient and rapid EPS production. Notably, bioreactor experiments revealed local maxima in EPS content at specific time points, suggesting that cell wall degradation, potentially induced by shear stress, may contribute to the release of polysaccharides into the culture broth.