From invasive waste biomass to value-added products: Cascade biorefinery processing of Ulex europaeus to oligosaccharides and antioxidants

Invasive lignocellulosic biomass poses a growing environmental challenge due to its accumulation and associated management costs. Among these, Ulex europaeus (gorse) is a highly flammable species that contributes to wildfire risk, requiring periodic removal and generating large volumes of underutilized waste. This study proposes a cascade biorefinery approach to convert gorse into value-added products through integrated processing. Microwave-assisted hydrothermal processing was applied and compared with conventional heating, achieving comparable oligosaccharide yields at lower nominal severity. These differences are discussed considering the distinct heating behavior of both systems. The processing enabled the selective solubilization of hemicellulose-derived compounds, mainly oligosaccharides, together with the co-extraction of phenolics. Downstream processing was performed using environmentally friendly technologies, including sequential membrane (5 and 1 kDa) and ion-exchange refining. Membrane processing generated oligosaccharide-rich streams (up to 83.70 % of non-volatile compounds, NVC), while removing monosaccharides (90 %) and other NVC (ONVC > 70 %). This separation was governed not only by molecular size, but also by structural features, including substitution patterns. Ion-exchange treatment enhanced purification by reducing ONVC (>98 %) while preserving oligosaccharide content, highlighting the presence of phenolics across process streams. As a result, high-purity oligosaccharide streams were obtained; together with secondary streams in which phenolics were concentrated in desorbed streams. Structural features by HPSEC, HPAEC and MALDI-TOF-MS revealed the presence of acetylated and uronic-containing xylooligosaccharides and their preferential association with higher-molecular-weight fractions. This cascade processing provides a pathway for the valorization of gorse into multiple high-value products, supporting efficient resource use and biomass management.