The digestibility of rapeseed protein isolate prepared by salt and alkali extraction: The importance of protein composition

In this study, four rapeseed protein extracts were prepared from intact/dehulled rapeseed using salt and alkaline extraction. Their nutritional quality was assessed and linked to protein composition through 4D label-free proteomics. Salt-extracted protein isolates had lower glucosinolate (0.47 μmol/g) and phytic acid (0.59 %) content than the alkaline-extracted protein isolates, whereas the alkaline-extracted isolates demonstrated higher digestibility (93 %). The inconsistency between the trend of non-protein anti-nutritional factors and protein digestibility suggests that protein composition may play a more significant role than anti-nutritional factors. Proteomic analysis showed that both extraction methods yielded similar globulin (cruciferin) abundance, but the salt-extracted isolate contained more protein anti-nutritional factors, including albumin (napin) and other protease inhibitors. These findings highlight the importance of protein composition in determining digestibility, showing the need for a protein composition-based approach in evaluating (plant) protein digestibility.