A green process for producing xylooligosaccharides from poplar: Endoxylanase assisted autohydrolysis, activated carbon separation, and spent liquor for rice growth

Abstract

This study proposed a clean sequential process, including autohydrolysis, the hydrolysis of endoxylanase, and adsorption with activated carbon (AC), that assisted refining poplar (Populus spp.) into low degree of polymerization (DP) xylooligosaccharides (XOS). First, autohydrolysis was conducted at 170 °C for 50 min. The autohydrolysate was then hydrolyzed with 1.0 International Unit (IU) per mL of endoxylanase to increase the concentration of low DP XOS (X2-X4) from 2.98 to 6.42 g/L. The recovery of XOS from the XOS rich enzymatic hydrolysis liquor reached 96.5% using 10% AC with a gradient elution of ethanol, and the highest purity of XOS was 98.2% from the 40% ethanol eluent. Finally, the separated spent liquor (SL) obtained after AC adsorption was assayed for bioactivity on rice (Oryza sativa L.). Spent liquor revealed a positive dose-dependent bioactivity toward rice growth, which promoted seed germination, plant height, root length and fresh weight. These effects were attributed to an appropriate amount of acetic acid and XOS, which could be used as plant biostimulants.