Xylooligosaccharides production from hardwood xylans: Effects of ball-milling and ozone pretreatments on enzymatic depolymerization

The biorefinery of hemicellulose is being explored to produce bioethanol and xylooligosaccharides from lignocellulosic materials. Among the various methods, enzymatic hydrolysis of xylans is recognized as an environmentally friendly approach. Utilizing by-products from the pulp and paper industry as substrates for xylanase enhances sustainability and reduces waste, providing a cost-effective raw material source. However, the direct application of xylanase on these substrates often yields low amounts of xylooligosaccharides. To address this, xylopentaose was used to evaluate reaction extent and accessibility, achieving a 61 % conversion and producing 57 % xylobiose (X2) and xylotriose (X3). Improvements in yield were observed when substrates were modified (by pretreatments), doubling the yield of X2 and X3 in commercial xylan to 44 %. In Kraft pulp treatment, ozonation increased yields from 18 % to 27 %. Different substrates required tailored pretreatments, such as ball milling for solid commercial xylan and ozone treatment for soluble xylan from Kraft pulp. Additionally, direct treatment of high-hemicellulose-content pulp converted 25 % of hemicellulose, with 44 % yielding X2 and X3, resulting in an overall yield of 11 %. These findings support the potential for industrial applications in biotechnological processes.