In vitro models of digestion are useful tools to explore the behavior of dietary fiber sources in gastrointestinal conditions. To evaluate the validity of our digestion model, digesta obtained in vivo and in vitro were characterized and the impact of cell wall integrity on protein bioaccessibility and digestibility evaluated. Six cannulated barrows [Pietrain × (Large White × Landrace)] were included in a 2 × 2 Latin square design where they were fed two diets identical in chemical composition but differing in nutrient bioaccessibility. Pea was given either as flour (R1, most proteins encapsulated by intact cell walls) or reconstituted flour (R2, mixture of proteins and purified, broken cell walls). Digesta were collected at the duodenal and ileal cannulas at regular interval and after slaughtering, following ingestion of either R1 or R2. The two diets were also digested in vitro using a static gastrointestinal model. The original pea ingredients as well as the digesta collected in vivo and in vitro were characterized (i.e., particle size measurement, microscopy observations and gel electrophoresis) and then compared with each other. The degradation of the pea ingredients differed greatly between the two forms of flour, where particles filled with nutrients were recovered at the latest stage of R1 intestinal digestion as observed with the particle size distribution and the microscopy images. These results were consistent with the in vivo and in vitro digestibility analysis that showed lower protein hydrolysis for R1 than that for R2 (about 19% difference in protein digestion regardless of the method). Overall, great similarities were found between the digesta collected in vivo and in vitro, especially regarding the particle size measurements. To summarize, a substantial proportion of the proteins contained in R1 was retained within the pea cells following gastrointestinal digestion. These encapsulated proteins reduced the amount of amino acids and small peptides available for absorption. This mechanism will have consequences on postprandial metabolism of amino acids and bacterial population based on the delivery form of the dietary fiber.
Keywords: cell wall; encapsulation; in vitro model; pea; pig; protein digestibility.
Although dietary fiber plays an essential role in the gastrointestinal health of pigs, it can also compromise the digestion and absorption of nutrients, especially of proteins. New ingredients such as pulses can be both good sources of protein and fiber, with no harmful effect for the animal or the environment, provided they are given in an adequate form (more or less structured). The objective of this work was to investigate how the dietary fibers (intact or broken down, encapsulation mechanism) of a pulse, pea, influenced the digestion of proteins. The approach of this study consisted in combining in vitro and in vivo studies with biochemical and biophysical techniques to determine how dietary fiber affected protein digestibility in pea flour. The results of this study showed good agreement between in vivo and in vitro data. Overall, breaking down of the dietary fibers led to 19% increase in protein digestion. These findings demonstrated that the form of ingestion of dietary fibers is crucial to optimize protein digestion. Moreover, our in vitro model of gastrointestinal digestion was capable of simulating pea degradation in pig during digestion and provide a good estimate of protein hydrolysis.
© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science.