Closed-loop biorefinery valorization of forage sorghum straw for xanthan gum production using a lignin-derived hydrogel for in-situ detoxification

This study presents a comprehensive biorefinery approach for the valorization of forage sorghum straw (FSS), an abundant residue from an industrial crop, by converting its cellulose and hemicellulose fractions into xanthan gum and developing a lignin-xanthan hydrogel as an adsorbent to improve the fermentation process. Organosolv pretreatment of FSS efficiently removed 49.9–57.1 % of lignin and 32.3–54.4 % of total solids. Fermentation of enzymatic hydrolysates from the cellulose fraction by Xanthomonas axonopodis MH1NC yielded 7.28 g/L of xanthan gum, while hemicellulosic hydrolysates also produced xanthan gum at 6.71 g/L. To enhance hemicellulose-derived xanthan gum production, a lignin-xanthan hydrogel—synthesized from organosolv lignin and FSS-derived xanthan—was used as an adsorbent to detoxify phenolic inhibitors. The hydrogel exhibited a phenolic adsorption capacity of 210 mg/g, following Freundlich isotherm behavior and pseudo-first-order kinetics. After detoxification, the hemicellulose-derived xanthan gum yield increased to 7.93 g/L. This work demonstrates a circular valorization strategy in which all biomass fractions contribute to value-added bioproducts, thereby improving both bioprocess efficiency and the economic sustainability of forage sorghum–based biorefineries. • A biorefinery was developed to convert forage sorghum straw into xanthan gum and lignin-xanthan hydrogel (LXH). • Organosolv pretreatment enhanced xanthan yield from cellulose by removing lignin. • LXH-mediated removal of phenolic inhibitors followed Freundlich isotherm and pseudo-first-order kinetics. • Detoxification with LXH improved hemicellulose-derived xanthan gum yield to 7.93 g/L.