The development of biorefinery processes to platform chemicals for most lignocellulosic substrates, results in side processes to intermediates such as oligosaccharides. Agrofood wastes are most amenable to produce such intermediates, in particular, cellooligo-saccharides (COS), pectooligosaccharides (POS), xylooligosaccharides (XOS) and other less abundant oligomers containing mannose, arabinose, galactose and several sugar acids. These compounds show a remarkable bioactivity as prebiotics, elicitors in plants, food complements, healthy coadyuvants in certain therapies and more. They are medium to high added-value compounds with an increasing impact in the pharmaceutical, nutraceutical, cosmetic and food industries. This review is focused on the main production processes: autohydrolysis, acid and basic catalysis and enzymatic saccharification. Autohydrolysis of food residues at 160-190 • C leads to oligomer yields in the 0.06-0.3 g/g dry solid range, while acid hydrolysis of pectin (80-120 • C) or cellulose (45-180 • C) yields up to 0.7 g/g dry polymer. Enzymatic hydrolysis at 40-50 • C of pure polysaccharides results in 0.06-0.35 g/g dry solid (DS), with values in the range 0.08-0.2 g/g DS for original food residues.Fermentation 2020, 6, 31 2 of 27 forestall engineering approaches, to name a few. Lignocellulosic biomass, of any origin is, therefore, a most promising raw material for biorefineries, considering such facilities as integrated refineries turning biomass into fuels, platform chemicals, food, feed and materials using integrated processes with an optimized used of resources [4]. This vision can be extended to resources of aquatic origin (seaweed, seagrass and microalgae) as well as residues from livestock [5,6]. In general, apart from forestall and energy crops biomass, most of it depends on the production of biomass and, in particular, food wastes [7,8]. While more than 100,000 M tons of biomass wastes are yearly produced [7], wastes strictly considered as food wastes (foods not consumed from any part of the food supply chain or any part of the food that is non edible and, therefore, becomes a residue) account for more than 1300 M tons each year [8]. The valorization of biomass wastes into a plethora of useful energy vectors, chemical compounds and ingredients receives a notable amount of interest from all stakeholders, including researchers and entrepreneurs. They are a source to several value-added products, such as monosaccharides (glucose, xylose, mannose, fructose, arabinose and more), oligosaccharides (fructoor FOS, xylo-or XOS, galacto-or GOS, galacturonic-or GALOS, lactosucrose, etc.), biofuels (ethanol, butanol, dimethylether -DME-, biodiesel, hydrogen), bioactive compounds (flavonoids, phenolic acids, terpenes, terpenoids, carotenoids), nanocellulose (bacterial, wood-related), lignin and its derivatives (a source of aromatics from biomass and prospective substitute of the aromatic or BTEX fraction produced in oil refineries) [8]. Oligomers from cellulose, hemicellulose, lignin, pectin and oth...
