Production of cellulase by Aspergillus niger through fermentation of spent mushroom substance: Glucose inhibition and elimination approaches

Abstract

In this study, the best activity of Aspergillus niger cellulase produced from spent mushroom substance (SMS) was 18.82 U/mL, and its enzymatic hydrolysis ability was similar to that of commercial cellulase (120.70 U/g) at the same enzyme loading. Moreover, A. niger cellulase remained stable at pH and temperature ranges of 4.0–8.0 and 40–60 ℃, respectively. Subsequently, the feedback inhibition by glucose on A. niger cellulase was analysed. When the glucose concentration reached 30 g/L, the activation energy of denaturation was 10.69% lower than that of the group with 0 g/L glucose, indicating that 30 g/L of glucose worsened the stability and decreased the activity of the enzyme. However, the kinetic results showed that glucose inhibition of A. niger cellulase was reversible. A. niger cellulase was used in the lactic acid (LA) fermentation of SMS. The activity of A. niger cellulase inhibited by sugars was recovered through sugar consumption by lactic acid bacteria in separate hydrolysis and fermentation, and the final saccharification yield increased from 81.04% to 87.71%. Under simultaneous saccharification and fermentation, the inhibition was avoided because the sugar concentration was < 10 g/L. Therefore, the final LA concentration and productivity were 31.98 g/L and 0.89 g/L/h, respectively.