Use of a gastrointestinal model to assess potential amino acid bioavailability in diets for rainbow trout (Oncorrhynchus mykiss)

The effect of different factors (protein composition, thermal treatment, presence of an acid-salt) on the potential bioavailability of amino acids (AAs) for intestinal absorption in rainbow trout diets was evaluated with a gastro-intestinal model (GIM). The in vitro assay consisted of a detailed evaluation of the rates of release of individual AAs, as well as of the whole AA profile of the dialysates produced after hydrolysis performed using enzyme extracts obtained from fish stomach and intestine. The results were compared to values of apparent amino acid digestibility measured in vivo. In addition, solubility and buffering capacity (BC) were evaluated, as they are major factors conditioning the potential bioaccessibility of dietary protein during digestion. Both parameters were significantly affected by the presence of a vegetable protein in the diet. As a result of enzyme hydrolysis, clear differences were detected in the release rates of release of different AAs, in particular for those that are targeted by digestive proteases (Arg, Lys, Phe). A significant correlation was obtained between the total mass of AAs dialysed in vitro and their digestibility estimated from digestibility coefficients calculated in vivo, although this was not possible when using values of individual AAs. The concept and framework for future assays involving in vitro-in vivo correlations is discussed.

► A two-step hydrolysis model using fish enzymes was operated.
► It was used to assess potential amino acid bioavailability in fish feeds.
► Total amount and rates of individual amino acid release were measured.
► Differences related to protein source and processing were evidenced.
► Results greatly correlated with amino acid digestibility measured in vivo.