Influence of Enzyme Loading and Physical Parameters on the Enzymatic Hydrolysis of Steam-Pretreated Softwood

• Published in: Biotechnology progress Vol. 17; no. 1; pp. 110 - 117
• Main Authors: Tengborg, Charlotte, Galbe, Mats, Zacchi, Guido
• Format: Journal Article
• Language: English
• Published: USA American Chemical Society 2001; American Institute of Chemical Engineers
• Subjects: Aspergillus - enzymology; Biofuel production; Biological and medical sciences; Biotechnology; Chemical Engineering; Chromatography, High Pressure Liquid; Energy; Engineering and Technology; Enzymes - metabolism; Fundamental and applied biological sciences. Psychology; Hot Temperature; Hydrogen-Ion Concentration; Hydrolysis; Industrial applications and implications. Economical aspects; Kemiteknik; Steam; Teknik; Trichoderma - enzymology; Wood; Ethanol; Enzyme; Cellulose; Biofuel; Softwood; Biomass; Glucose; Water vapor; Optimization; Operating conditions; Hydrolysis; β-Glucosidase; Cellulase; Glycosidases; Hydrolases; Pretreatment; O-Glycosidases; Enzymatic reaction
• ISSN: 8756-7938; 1520-6033; 1520-6033
• DOI: 10.1021/bp000145+

Softwood is an interesting raw material for the production of fuel ethanol as a result of its high content of hexoses, and it has attracted attention especially in the Northern hemisphere. However, the enzymatic hydrolysis of softwood is not sufficiently efficient for the complete conversion of cellulose to glucose. Since an improvement in the glucose yield is of great importance for the overall economy of the process, the influence of various parameters on the cellulose conversion of steam‐pretreated spruce has been investigated. The addition of β‐glucosidase up to 50 IU g−1 cellulose to the enzymatic hydrolysis process resulted in increased cellulose conversion at a cellulase loading up to 48 FPU g−1 cellulose. Despite very high enzyme loading (120 FPU g−1 cellulose) only about 50% of the cellulose in steam‐pretreated spruce was converted to glucose when all of the material following pretreatment was used in the hydrolysis step. The influence of temperature, residence time, and pH were investigated for washed pretreated spruce at a dry matter (DM) content of 5% and a cellulase activity of 18.5 FPU g−1 cellulose. The optimal temperature was found to be dependent on both residence time and pH, and the maximum degree of cellulose conversion, 69.2%, was obtained at 38 °C and pH 4.9 for a residence time of 144 h. However, when the substrate concentration was changed from 5% to 2% DM, the cellulose conversion increased to 79.7%. An increase from 5% to 10% DM resulted, however, in a similar degree of cellulose conversion, despite a significant increase in the glucose concentration from 23 g L−1 to 45 g L−1. The deactivation of β‐glucosidase increased with increasing residence time and was more pronounced with vigorous agitation.