Valorization of sorghum stalk lignocellulose for xylooligosaccharide production: process optimization and...

Sorghum stalk (Sorghum bicolor) represents an abundant and underutilized lignocellulosic biomass with significant potential for the generation of value-added bioproducts within biorefinery systems. In the present study, sorghum stalk (SS) biomass was valorized for the production of xylooligosaccharides (XOS) through alkaline extraction of xylan, followed by enzymatic hydrolysis. SS was treated with alkali to extract high-purity xylan, where increasing NaOH concentrations significantly (p < 0.05) enhanced xylan recovery. Fourier-transform infrared spectroscopy indicated that xylan extracted using 3 M NaOH contained minimal lignin and represented a higher recovery (87.17 ± 0.32%). Enzymatic hydrolysis of extracted xylan, as optimized using Design-Expert software, resulted in maximum XOS production at pH 5.5, 45.45 °C, 24 h incubation, and an enzyme dose of 20 IU per 200 mg xylan. Analytical characterization revealed that the hydrolysates predominantly contained XOS with a degree of polymerization ranging from 2 to 6, primarily composed of xylohexaose. The produced XOS exhibited promising prebiotic potential for Lactobacillus salivarius, as evidenced by a higher prebiotic index (1.74 ± 0.04) than galacto-oligosaccharides (1.12 ± 0.03) and inulin (1.27 ± 0.08), together with the highest prebiotic activity score (13.42 ± 0.27) under the experimental conditions evaluated. The XOS also demonstrated concentration-dependent gradual increase in DPPH scavenging capacity, ranging from 23.02% at 0.125 mg/mL to 75.83% at 4 mg/mL. Furthermore, the XOS showed a higher resistance to simulated gastric conditions (pH 1-5), with less than 6% hydrolysis after 6 h. Overall, the findings highlight SS as a promising lignocellulosic biomass for the sustainable production of XOS and support their potential as high-value bioproducts derived from agricultural residues.