Production, characterization and isolation of neutral and pectic oligosaccharides with low molecular weights from olive by-products thermally treated

Alperujo was pre-treated in a hydrothermal reactor to solubilize the oligosaccharides. The liquid was extracted with ethyl acetate to remove the phenols, and then its sugar content was sequentially precipitated with ethanol:water solutions and ultrafiltered, obtaining oligosaccharide fractions in the range of 3000 to 1000 Da that represent 23% of the total. One of the two major fractions was rich in pectic polymers, and the composition of the other fraction indicated the possible presence of xyloglucans and xylo-oligosaccharides. Hydrolysis was used to decrease the molecular weight of oligosaccharides by means of TFA or HCl for the neutral or enzymes for the pectic oligosaccharides. They were isolated by adsorption and size exclusion chromatography and identified by HPLC, GC, ESI-MS and MS/MS. The presence of tetra-, tri- and di-galacturonic acids was confirmed, and different structures for neutral and acidic xylo-oligosaccharides and oligosaccharides of xyloglucan with low molecular weight have been proposed.