Pea cell wall polysaccharides and their structural integrity influence protein bioaccessibility and hydrolysis

Pea cell walls have been shown to encapsulate nutrients inside cells, thereby limiting their hydrolysis by digestive enzymes. However, it is unknown how the cell wall performs this barrier function. In particular, this could be due to the presence of specific polysaccharides or, most probably, the organisation of the components within the cell wall. This study aimed to investigate how cell walls prevented protein hydrolysis. To address this objective, isolated cells were obtained using different treatments thought to affect cell walls differently (incubations in water, salt or EDTA solutions) and digested in vitro using a three-phase (oral, gastric and intestinal) model. Purified polysaccharides (cellulose, rhamnogalacturonan I and xyloglucan) and solutions obtained from the incubation of pea fibres and flour were also used in our digestion experiments. We found that protein bioaccessibility (here defined as the amount of protein released from the pea cells) and hydrolysis was lower after the gastric phase for the isolated cells prepared with the salt solution compared to the other treatments. Regardless of the treatment, between 47% and 93% of proteins were released from the cells (bioaccessible) and hydrolysed, respectively. Therefore, after prolonged incubation time proteases seem to be able to penetrate the cells during digestion. In terms of purified polysaccharides, rhamnogalacturonan I had the greatest effect on protein hydrolysis. Incubation solutions made from the pea fibres reduced proteolysis to a greater extent than the pea flour. The present study showed that pea cell walls delay protein digestion mainly via its structural organisation within the cell wall, with purified polysaccharides having a more limited effect.