Comparative analysis of pretreatment methods on sorghum (Sorghum durra) stalk agrowaste for holocellulose content

Abstract

This study compares different types of pretreatment methods, such as thermal pretreatment at 120 °C, autoclaving, microwaving and ultrasonication in the presence of water, dilute acid (1% H₂SO₄) or dilute alkali (1% NaOH) on Sorghum stalk with respect to the holocellulose and Acid Detergent/Insoluble Lignin content. Among all the methods, pretreatment with 1% NaOH along with autoclaving at 121 °C and 15 psi for 30 min was the most effective method for Sorghum stalk. Fourier Transform Infra-Red spectroscopy analysis of this pretreated biomass showed the removal of lignin and Field Emission Scanning Electron Microscope analysis displayed enhanced surface roughness. The enzymatic hydrolysis of raw and best pretreated Sorghum stalk using recombinant endo-β-1,4-glucanase (CtCel8A) and β-1,4-glucosidase (CtBgl1A) both from Clostridium thermocellum gave glucose yields, 22.4 mg/g raw biomass and 34 mg/g pretreated biomass, respectively, resulting in 1.5-fold increase of glucose yield after the pretreatment.

Keywords:

• Acid insoluble lignin
• enzymatic hydrolysis
• FESEM
• holocellulose
• pretreatment
• Sorghum stalk

Acknowledgments

The authors acknowledge the use of FTIR spectrophotometer procured through the Indo-Finnish project grant (BT/IN/Finland/08/AG/2011) from Department of Biotechnology (DBT), Ministry of Science and Technology, Government of India to AG, XRD at Department of Chemical Engineering and FESEM at Central Instrumental Facility, IIT Guwahati, India.

Additional information

Funding

The research work was financially supported by DBT-Pan-IIT Grant (BT/EB/PAN IIT 2012), Centre for Bioenergy from Department of Biotechnology, Ministry of Science and Technology, New Delhi, India to Prof. Arun Goyal.