Effect of Dietary Fibre Fractions on In Vitro Digestibility of Rapeseed Napin Proteins

Key words: in vitro protein digestibility, total dietary fi bre, rapeseed napin proteins, plant food ingredients Protein digestibility may be infl uenced by the presence of dietary fi bre affecting the nutritional quality of a feed or food product. This study investigated the interplay between rapeseed (Brassica napus L.) protein and fi bre constituents separated by industrially scalable pilot plant processing and recombined in mixed samples. Total dietary fi bre (TDF) fractions were isolated from rapeseed hulls (TDF-RH) and purifi ed rapeseed embryo fi bres (TDF-RE). The effect of TDF sources on in vitro protein digestibility (IVPD) of a rapeseed protein concentrate rich in napin proteins (RP2) was assessed at three inclusion levels (200, 333, and 500 mg/g DM) using a sequential transient proteolysis by pepsin (1 h) and pancreatin (1 h). The IVPD of RP2 was dose-dependently decreased upon addition of hull fi bres at all inclusion levels (8.9-26.6%; P<0.05), whereas the effect of embryo fi bres was of a markedly lower magnitude and only signifi cant at the medium to high levels (7.3-8.9%; P<0.05). These results demonstrated that TDF fractions obtained from rapeseed differentially affect the protein digestibility of rapeseed napin proteins depending on the fi bre source and inclusion level.