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

Abstract

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