Manufacturing of hemicellulosic oligosaccharides from fast-growing Paulownia wood via autohydrolysis: Microwave versus conventional heating

Abstract

Microwave hydrothermal treatment (MHT) is considered a sustainable technology for the valorization of lignocellulosic materials, enabling the solubilization of hemicellulosic-derived compounds, especially in the form of oligosaccharides that may present potential in the chemical, pharmaceutical or nutraceutical industries. Hence, MHT at 200 and 230 °C, at severity (S 0 ) among 2.92–4.66 were performed. S 0 = 3.98 permitted the recovery of about 80% of the initial xylan as xylooligosaccharides. In order to compare the effectiveness of MHT, conventional hydrothermal treatment (CHT) was performed at conditions leading to the maximum recovery of oligosaccharides (S 0 =3.98, non-isothermal regime at 203 °C). Despite the structural features of oligomers in the three liquors were very similar, the spent solids presented different enzymatic digestibility, which implied a different effect of the treatments, reaching up to 80% of glucan to glucose conversion for the solid after MHT at 230 °C for 0.5 min. Additionally, CHT consumed 2.1–2.8-fold greater energy than MHT, reflecting that microwave-assisted autohydrolysis is a sustainable and efficient technology to process PW. • Microwave (MHT) and conventional (CHT) hydrothermal treatments were evaluated. • Up to 80% xylan conversion into xylooligosaccharides via hydrothermal treatments. • Polyphenolic profile of Paulownia extracts was identified via HPLC-ESI-MS. • Glucose conversions of 64–80% after saccharification of MHT and CHT solids. • Up to 64.7% energy is saved using MHT comparing to CHT.