Strategies for valorization of quinoa stalks in an integrated biorefinery approach: Citric acid-assisted hydrothermal pretreatment, membrane separation, production, and use of activated charcoal

Quinoa ( Chenopodium quinoa ), a widely consumed grain, generates quinoa stalks (QS), a byproduct rich in valuable components such as carbohydrates. This study explores the use of citric acid-assisted hydrothermal pretreatment (CA-HTP) to produce glucose through enzymatic hydrolysis of pretreated QS and to recover xylooligosaccharides (XOS). Additionally, QS was converted into activated charcoal to remove phenolic compounds, and XOS were subsequently purified using ultrafiltration (UF) and nanofiltration (NF). After CA-HTP treatment (at 180°C for 60 minutes with 3.5 % citric acid concentration), followed by enzymatic hydrolysis, 43.5 g of glucose per 100 g of pretreated material was obtained. Furthermore, a secondary hydrothermal treatment (HTP) step using water increased glucan hydrolysis yield by 26 %. Optimization of CA-HTP conditions (180°C for 20 minutes, 7.1 % solid-to-liquid ratio, and 2 % citric acid) resulted in the production of 17.1 mg of XOS per gram of washed QS. Activated charcoal treatment of the CA-HTP hydrolysate removed 87.62 % of phenolic compounds, recovering 62 % of XOS at 47 % purity after membrane filtration. These results demonstrate the potential of quinoa stalks for sustainable valorization in biorefinery applications. • Global Chenopodium quinoa cultivation increased, resulting in more residue generation. • Citric acid-assisted hydrothermal process efficiently improves enzymatic hydrolysis of cellulose. • Use of citric acid as catalyst improve and accelerate the XOS production. • Activated charcoal produced from quinoa stalks remove efficiently the phenolic compounds.