Enzymatic Hydrolysis Of Corn Stalks By Combined Cellulase And Extracellular Extract From White-rot Fungi

Basidiomycetes which have a complete ligninocellulose-degrading system have an advantage for the degradation of lignocellulose in natural state. So, it was possible to construct a complex enzyme system with the enzymes of basidiomycetes and commercial cellulases. This work evaluated the effect of extracellular extract from basidiomycetes on enzymatic hydrolysis of corn stalks to construct the complex enzyme system with extracellular extract from Echinodontium taxodii 2538 and cellulase. Further, influence factors and main effect factor which affected complex enzymatic hydrolysis were also investigated. Simultaneously, the preliminary mechanism of enzymatic hydrolysis by combination of commercial cellulase with extracellular extract was revealed.The effect of extracellular extract from 5 strains of basidiomycetes incubated in submerged fermentation medium(SmF) and solid-state fermentation medium(SSF) was systematically evaluated. The result showed that the extracellular extract from Echinodontium taxodii 2538 incubated for 5 days in SSF culture increased cellulase hydrolysis of corn stalks. The synergistic action between extracellular extract and cellulase was found in complex enzymatic hydrolysis. The main influence factors which affected synergistic enzymatic hydrolysis were studied. The result showed that the hydrolysis yields of corn stalks at 45℃were significantly increased by 0.14-fold (acid-treated corn stalks), 0.27-fold (alkaline-treated corn stalks) and 0.27-fold (raw corn stalks) compared to that of sole cellulase hydrolysis. At the presence of oxygen, hydrolysis yields of acid-treated corn stalks and raw corn stalks which had high lignin content were further improved by complex enzyme system, and the saccharification yields were increased 0.63-fold and 0.80-fold respectively. However, alkaline-treated corn stalks with low lignin content were promoted by complex enzyme system at the presence of oxygen. In the synergistic enzymatic hydrolysis, extracellular extract from E. taxodii 2538 could not change cellulase activity. On the contrary, pretreatment of acid-treated, alkaline-treated and raw corn stalks by extracellular extract could improve the rate of reactive polysaccharides, increasing by 0.87-fold, 0.24-fold and 0.47-fold respectively compared to the control. These suggested that extracellular extract of E. taxodii 2538 could significantly decrease the enzymatic resistance of corn stalks. Therefore, the decrease of resistance play an important role in synergistic enzymatic hydrolysis.To determine the main effect factor increasing enzymatic hydrolysis, the effect of extracellular enzymes and low-molecular-weight substances from E. taxodii 2538 on cellulase hydrolysis of corn stalks were evaluated. The result showed that cellulase hydrolysis of corn stalks were inhibited by extracellular enzymes. And the inhibition was improved by the increased content of extracellular enzymes. However, low-molecular-weight substances could improve cellulase hydrolysis of corn stalks, and hydrolysis yields for 24 hours in the presence of oxygen were increased respectively by 0.83-fold (acid-treated corn stalks), 0.24-fold (alkaline-treated corn stalks) and 0.68-fold (raw corn stalks) compared to control. Therefore, low-molecular-weight substances could play an important role in the synergistic hydrolysis.