Liquid chromatography-mass spectrometry investigation of enzyme-resistant xylooligosaccharide structures of switchgrass associated with ammonia pretreatment, enzymatic saccharification, and fermentation

► The first report of HILIC-MS/MS analysis of biomass-derived SSF residues. ► Residual xylooligosaccharides were neither linear nor contained phenolic esters. ► Putative structures were assigned from MS/MS data of residual oligosaccharides. ► Non-hydrolyzed glycosidic bonds after pretreatment and SSF were identified.