High xylan recovery using two stage alkali pre-treatment process from high lignin biomass and its valorisation to xylooligosaccharides of low degree of polymerisation

• Published in: Bioresource technology 2018-05, Vol.256, p.110-117
• Main Authors: Singh, R.D., Banerjee, J., Sasmal, S., Muir, J., Arora, A.
• Format: Article
• Language: English
• Subjects: Alkalies; Alkaline pretreatment; Arecanut husk; Biomass; Endo-1,4-beta Xylanases; Enzymatic hydrolysis; Glucuronates; Hydrolysis; Hydrothermal pretreatment; Lignin; Oligosaccharides; Xylans; Xylooligosaccharides
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2018.02.009

•Two stage alkali pretreatment process was optimized to maximize xylan recovery.•Optimized conditions for 1st stage: 10% w/v NaOH, incubated at 65 °C for 8 h.•Optimized conditions for 2nd stage: Hydrothermal treatment (121 °C for 1 h).•Enzymatic hydrolysis of xylan yielded 35 g/100 g pure xylan at optimized conditions.•XOS was rich in xylobiose (71% of XOS) and xylotriose (26%). In the present work, xylan from arecanut husk was extracted using 2 stage alkaline pretreatment process. In first step, biomass was incubated in alkali at different temperatures (25 °C, 50 °C and 65 °C), alkali concentrations (5%, 10%, 15% and 20% w/v), and incubation periods (8 h, 16 h and 24 h) and evaluated for xylan recovery. It was observed that 40–52% of available xylan could be recovered using 10% alkali when incubated for 8–24 h at 65 °C. Subsequently, the alkali pretreatment operating conditions which provided good xylan recovery were processed further using hydrothermal treatment to extract more xylan. For maximum xylan recovery (>90%), best operating conditions were identified when biomass was treated under hydrothermal treatment (1, 1.5 and 2 h) with varying incubation periods (8, 16, 24 h) and alkali concentrations (5%, 10%) using full factorial design. Incubating arecanut husk with 10% w/v NaOH, at 65 °C for a period of 8 h, followed by hydrothermal treatment at 121 °C for 1 h helped recover >94% xylan. In the next step, enzymatic hydrolysis process was optimized to recover maximum XOS (Optimized condition: 50 °C, pH 4 and 10 U enzyme dose). The hydrolysate comprised of xylobiose: 25.0 ± 1.2 g/100 g xylan (∼71% of XOS), xylotriose: 9.2 ± 0.65 g/100 g xylan (26.2% of XOS) and xylotetrose: 0.9 ± 0.04 g/100 g xylan (2% of XOS). The developed process enables to reduce alkali consumption for high recovery of xylan from biomass with relatively higher lignin content for its valorisation into a potential prebiotic oligosaccharide.