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Lignocellulosic wastes have the ability to be transformed into oligosaccharides and other value-added products. The synthesis of oligosaccharides from renewable sources bestow to growing bioeconomies. Oligosaccharides are synthesized chemically or biologically from agricultural residues. These oligosaccharides are functional food supplements that have a positive impact on humans and livestock. Non-digestible oligosaccharides, refered as prebiotics are beneficial for the colonic microbiota inhabiting the f the digestive system. These microbiota plays a crucial role in stimulating the host immune system and other physiological responses. The commonly known prebiotics, galactooligosaccharides (GOS), xylooligosaccharides (XOS), fructooligosaccharides (FOS), mannanooligosaccharides (MOS), and isomaltooligosaccharides (IOS) are synthesized either through enzymatic or whole cell-mediated approaches using natural or agricultural waste substrates. This review focusses on recent advancements in biological processes, for the synthesis of oligosaccharides using renewable resources (lignocellulosic substrates) for sustainable circular bioeconomy. The work also addresses the limitations associated with the processes and commercialization of the products., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The empirical models developed through two independent RSM (RSM-I, 2(3); RSM-II, 2(5)) in terms of effective operational factors of inoculum age, inoculum volume, wheat bran-to-moisture ratio (RSM-I) and contact time, extraction temperature, agitation, fermented bran-to-solvent ratio and SDS (RSM-II) were found adequate to describe the optimization of exo-polygalacturonase from Bacillus subtilis RCK under solid-state fermentation (SSF) conditions. Through the analysis of RSM-I, wheat bran-to-moisture ratio and inoculum volume were found to be the most significant factors and an increment in both had a positive effect in enhancing enzyme yield, while in RSM-II all the factors significantly affected enzyme recovery except fermented bran-to-solvent ratio, which had the least impact within the ranges investigated in enhancing enzyme recovery. Based on contour plots and variance analysis, optimum operational conditions for maximum exo-polygalacturonase yield were achieved when 1.5% (v/w) of 24h old (OD(600 nm) approximately 2.7+/-0.2) B. subtilis RCK cells were inoculated on moistened wheat bran (1:7 solid substrate-to-moisture ratio) and enzyme was harvested by addition of solvent (1:6 fermented bran-to-solvent ratio) under shaking conditions (200 rpm) in presence of SDS (0.25% w/v) for 15 min at 35 degrees C. An over all 3.4 fold (1.7-fold RSM-I; 2.0 fold RSM-II) increase in enzyme production was attained because of optimization by RSM.