BACKGROUND: Although several types of in vitro digestibility assays have been applied to nutritional evaluation of feeds for aquatic organisms, all of them are based on the use of closed reactors and do not simulate the gastric phase of the digestion. Our objective was to evaluate the suitability of a gastrointestinal model based on the use of a digestion cell provided by a semi-permeable reaction chamber, which allows continuous removal of digestion products as they are produced. We tested the effects of some factors, like the inclusion of a gastric phase, reaction temperature or bile salts on the hydrolysis of feed proteins by fish enzymes.
RESULTS: We found that the most suitable operational conditions to simulate the digestion process must include a short acid pre-digestion as well as the use of bile salts in the reaction mixture. Acid pre-digestion resulted in a significant increase in the liberation of amino acids which represented more than twice that measured when using a single phase. The addition of two bile salts (45 µmol L−1 sodium taurocholate + chenodesoxycolate) resulted in almost a threefold increase in the hydrolysis of feed protein. The use of the described open system also allows the evaluation of carbohydrate hydrolysis as well as determination of residual undigested matter, in a similar manner to that carried out in ruminants with the DAISY system.
CONCLUSION: Results suggest the system can be a very suitable model for evaluation of bioaccessibility in fish feeds. Copyright © 2009 Society of Chemical Industry