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

•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 o...

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Bibliographic Details
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:
Alkaline pretreatment
Arecanut husk
Enzymatic hydrolysis
Hydrothermal pretreatment
Xylooligosaccharides
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Summary:•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.
ISSN:0960-8524
1873-2976
DOI:10.1016/j.biortech.2018.02.009