(503b) Top-Down Synthesis of Potential Prebiotic Gluco- and Xylo-Oligosaccharides from Corn Stover Via Simultaneous Hydrolysis and Glycosylation in Concentrated Sulfuric Acid

Valorization of lignocellulosic biomass residues into functional oligosaccharides with prebiotic activity has attracted great interest from both environmental and economic perspectives. Cellulose and hemicelluloses, the two structural polysaccharides naturally present in the matrix of lignocellulosic biomass, can be depolymerized into soluble oligosaccharides, such as cello-oligosaccharides and xylo-oligosaccharides (XOS), which are non-digestible and fermentable by the health-promoting gut microbiota, making them potential prebiotics. Currently, XOS are industrially produced from corncob xylan via alkaline extraction followed by enzymatic hydrolysis by xylanases. However, cellulose (~30% in corncob) remains unutilized, and the process economy is limited by the high cost associated with enzymes and the pretreatment step. Herein, we report a facile and efficient chemical method (top-down synthesis) for the co-production of potential prebiotic gluco-oligosaccharides (GlcOS) and XOS mixtures from unpretreated corn stover. Specifically, cellulose and xylan in corn stover are subject to simultaneous hydrolysis and glycosylation (SHG) in concentrated sulfuric acid (60–84%) under mild conditions (50–70 °C, 5–60 min). After the removal of lignin residues, a soluble oligosaccharide product is obtained, which is identified as a mixture of GlcOS and XOS with mostly 2–6 monomer units, linked by diverse glycosidic linkages (α- and β-(1→6/4/3/2/1)). The total yield of corn stover-derived oligosaccharides (CS-OS) is close to the theoretical yield, with minimal loss into monosugars and acid-induced degradation products (e.g., furfural, 5-hydroxymethylfurfural). The prebiotic activity of CS-OS was assessed via in vitro fermentation with different lactic acid bacteria. CS-OS could promote the growth of certain Lactobacillus and Pediococcus strains (potential probiotics), outperforming two commercial prebiotic oligosaccharides (fructo- and isomalto-oligosaccharides). Furthermore, a mechanism study was conducted to reveal the impact of oligosaccharide size (degree of polymerization, DP) and glycosidic linkages on their utilization by probiotic bacteria. Preferrable utilization of DP 2–3 over DP 4–7 oligosaccharides was observed, and the bacterial ability to utilize α/β-(1→6/4) linkages varies significantly depending on the available genomes essential for oligosaccharide transport and catabolism. Overall, this study demonstrated the production of value-added oligosaccharides as potential prebiotics from lignocellulosic biomass, which is an emerging sector in response to the burgeoning market of prebiotics.