Production efficiency versus thermostability of (hemi)cellulolytic enzymatic cocktails from different cultivation systems

• Novel cost-effective bioprocesses for cellulolytic enzymes production are needed.
• Cultivation conditions should be accompanied by characterization of the thermostability.
• Phenolic compounds released after biomass pretreatment restricted fungal growth.
• Improved enzyme production requires the removal of inhibitors from the pretreated biomass.
• Cellulases produced under SSF were less prone to deactivation by phenolics.

High productivity and enzyme stability are desirable characteristics of bioprocesses for production of the (hemi) cellulolytic enzymes needed for biomass conversion. This paper reports a comparative study of different cultivation systems, investigating production efficiency and the thermostability of the (hemi) cellulolytic enzymatic cocktails. A selected strain of Aspergillus niger was cultivated using a novel sequential fermentation (SF) technique as well as the conventional submerged (SmF) and solid-state fermentation (SSF) methods. Enzyme production and thermostability were evaluated considering the effects of pretreatment (using steam-explosion and liquid hot water) of the sugarcane bagasse used as carbon source and inducer. For endoglucanase and xylanase enzymes, cultivation under SSF favored production when using washed steam-exploded bagasse and liquid hot water-pretreated bagasse as the solid substrates. However, removal of inhibitors from the pretreated biomass employed in the cultivation media was necessary, because the presence of phenolic compounds restricted fungal growth. It was concluded that the cultivation conditions should be conducted in conjunction with characterization of the thermostability of the enzymes, due to the inverse relation that can exist between these two process criteria. The findings revealed that endoglucanase and β-glucosidase produced under SSF were less prone to deactivation by the phenolics in the medium. The residual activities of such enzymes after 24 h of incubation at 50 °C were between 80 and 100%, indicating that they are highly thermostable. The results emphasize the potential of SSF for the production of (hemi) cellulolytic enzymes that are more stable.

Thermostability and residual enzymatic activity at 50 °C and pH 4.8 of endoglucanase present in the (hemi) cellulolytic complexes produced by A. niger after cultivation under SSF using different types of pretreated sugarcane bagasse (SEB, SEBw, and LHWB).Figure optionsDownload as PowerPoint slide