Extraction of sugarcane bagasse arabinoxylan, integrated with enzymatic production of xylo-oligosaccharides and separation of cellulose

Leila Khaleghipour; Javier A Linares-Pastén; Hamid Rashedi; Seyed Omid Ranaei Siadat; Andrius Jasilionis; Said Al-Hamimi; Roya R R Sardari; Eva Nordberg Karlsson

doi:10.1186/s13068-021-01993-z

Extraction of sugarcane bagasse arabinoxylan, integrated with enzymatic production of xylo-oligosaccharides and separation of cellulose

Biotechnol Biofuels. 2021 Jul 3;14(1):153. doi: 10.1186/s13068-021-01993-z.

Authors

Leila Khaleghipour^{1

2}, Javier A Linares-Pastén¹, Hamid Rashedi³, Seyed Omid Ranaei Siadat⁴, Andrius Jasilionis¹, Said Al-Hamimi⁵, Roya R R Sardari¹, Eva Nordberg Karlsson⁶

Affiliations

¹ Division Biotechnology, Department of Chemistry, Lund University, P. O. Box 124, 22100, Lund, Sweden.
² Biotechnology Group, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
³ Biotechnology Group, School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran. hrashedi@ut.ac.ir.
⁴ Protein Research Center, ShahidBeheshti University, G. C., Tehran, Iran.
⁵ Center for Analysis and Synthesis, Department of Chemistry, Lund University, P. O. Box 124, 22100, Lund, Sweden.
⁶ Division Biotechnology, Department of Chemistry, Lund University, P. O. Box 124, 22100, Lund, Sweden. eva.nordberg_karlsson@biotek.lu.se.

Abstract

Sugarcane processing roughly generates 54 million tonnes sugarcane bagasse (SCB)/year, making SCB an important material for upgrading to value-added molecules. In this study, an integrated scheme was developed for separating xylan, lignin and cellulose, followed by production of xylo-oligosaccharides (XOS) from SCB. Xylan extraction conditions were screened in: (1) single extractions in NaOH (0.25, 0.5, or 1 M), 121 °C (1 bar), 30 and 60 min; (2) 3 × repeated extraction cycles in NaOH (1 or 2 M), 121 °C (1 bar), 30 and 60 min or (3) pressurized liquid extractions (PLE), 100 bar, at low alkalinity (0-0.1 M NaOH) in the time and temperature range 10-30 min and 50-150 °C. Higher concentration of alkali (2 M NaOH) increased the xylan yield and resulted in higher apparent molecular weight of the xylan polymer (212 kDa using 1 and 2 M NaOH, vs 47 kDa using 0.5 M NaOH), but decreased the substituent sugar content. Repeated extraction at 2 M NaOH, 121 °C, 60 min solubilized both xylan (85.6% of the SCB xylan), and lignin (84.1% of the lignin), and left cellulose of high purity (95.8%) in the residuals. Solubilized xylan was separated from lignin by precipitation, and a polymer with β-1,4-linked xylose backbone substituted by arabinose and glucuronic acids was confirmed by FT-IR and monosaccharide analysis. XOS yield in subsequent hydrolysis by endo-xylanases (from glycoside hydrolase family 10 or 11) was dependent on extraction conditions, and was highest using xylan extracted by 0.5 M NaOH, (42.3%, using Xyn10A from Bacillus halodurans), with xylobiose and xylotriose as main products. The present study shows successful separation of SCB xylan, lignin, and cellulose. High concentration of alkali, resulted in xylan with lower degree of substitution (especially reduced arabinosylation), while high pressure (using PLE), released more lignin than xylan. Enzymatic hydrolysis was more efficient using xylan extracted at lower alkaline strength and less efficient using xylan obtained by PLE and 2 M NaOH, which may be a consequence of polymer aggregation, via remaining lignin interactions.

Keywords: Alkali extraction; Enzymatic hydrolysis; Sugarcane bagasse; Thermostable xylanases; Xylan; Xylo-oligosaccharides.

Grants and funding

NNF18OC0034792/Novo Nordisk Fonden