(254a) Chemical Synthesis of Potential Prebiotic Oligosaccharides from Simple Sugars and Lignocellulosic Biomass in Concentrated Acids

Prebiotics are non-digestible compounds that modulate the composition and/or activity of the gut microbiota through their selective fermentation by microorganisms in the gut, thus conferring health benefits to the host. Non-digestible oligosaccharides like fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), isomalto-oligosaccharides (IMO), xylo-oligosaccharides (XOS), and manno-oligosaccharides (MOS) have been recognized as prebiotics, and they have been commercially produced for application in functional food/drinks and dietary supplements. It is highly attractive to develop efficient processes for large-scale production of prebiotic oligosaccharides from inexpensive and abundant substrates. For this purpose, we developed chemical methods for the synthesis of potential prebiotic oligosaccharides from biomass-derived simple sugars (bottom-up process) or directly from lignocellulosic biomass (top-down process) in concentrated acid systems. In the bottom-up synthesis strategy, gluco-oligosaccharides (GlcOS) were synthesized from glucose via dehydration condensation (acid-catalyzed glycosylation) in concentrated sulfuric acid (SA, 60–92%) with a high single-pass yield of GlcOS (83%) at 70 °C for 20 min. The synthesized GlcOS were a mixture of disaccharides (44%), trisaccharides (22%), tetrasaccharides (13%), and higher oligosaccharides (DP 5-9). The glucose residues in GlcOS were linked by predominantly α- and β-(1→6) linkages and other linkages including (1→4), (1→3), (1→2), and (1→1). The in vitro fermentation of GlcOS by probiotic bacteria Bifidobacterium bifidum, Bifidobacterium animalis, and Limosilactobacillus reuteri suggested that GlcOS could be utilized as a carbon source for bacterial growth, and their promotion effect was comparable to the commercial prebiotic IMO. It was found that concentrated phosphoric acid (PA, 70-85%) was as efficient as concentrated SA for GlcOS synthesis. Different oligosaccharides were also successfully synthesized from other mono- and di-saccharides (e.g., galactose, xylose, arabinose, lactose, maltose, and cellobiose) in the concentrated acid systems. In the top-down synthesis strategy, GlcOS and XOS/MOS were synthesized from cellulose and hemicelluloses (xylan or mannan) in lignocellulosic biomass (corn stover) via simultaneous hydrolysis and glycosylation in concentrated SA/PA.