Unfermented recalcitrant polysaccharide structures from rapeseed (Brassica napus) meal in pigs

•Water-soluble carbohydrates were almost completely fermented.•Residual pectins were mainly rhamnogalacturonan and branched arabinan.•Residual hemicelluloses were mainly xyloglucan, xylan and galactomannan.•Carbohydrates could be linked via alkali-labile interaction in cellulose-lignin network. Unprocessed and acid-extruded rapeseed meal (RSM) was fed to pigs as the only source of non-starch polysaccharides (NSP) and protein. Unfermented carbohydrate structures were analyzed. Acid-extrusion seemed to increase rigidness of the NSP-matrix in vivo, without affecting NSP-fermentability. Water-soluble NSP were almost completely fermented in the colon. From the water-insoluble unfermented carbohydrates 46–68% (w/w) was analyzed as the polysaccharides rhamnogalacturonan, (branched) arabinan, XXXG-type xyloglucan, linear xylan, galactomannan, and cellulose. A major fraction (35–54% w/w) of the unfermented carbohydrates was unexpectedly released as small uronyl-rich carbohydrates (