Application of an in vitro gastrointestinal model to evaluate nitrogen and phosphorus bioaccessibility and bioavailability in fish feed ingredients

In the present work a gastrointestinal model (GIM) designed to reproduce closely the conditions existing in the gut of live fish was used to evaluate differences in bioaccessibility and bioavailability of nitrogen and phosphorus present in two different feedstuffs (fish meal and soybean meal) as a result of the action of rainbow trout digestive enzymes. In contrast to previous similar works, the operating conditions are established considering the enzyme:substrate ratio estimated from data obtained from live fish, as well as pH changes taking place during digestion. In addition, the GIM allows evaluation of other important parameters, like the solubilisation of proteins and phosphorus, or the relative contribution of the enzymes to total bioavailability of those nutrients. The results obtained showed the key role of the gastric digestion on further intestinal bioavailability of N and P. and clearly established the higher biological value of the fish meal compared to the soybean meal tested. Considering its versatility and the great amount of information which it can provide, the use of this GIM is suggested as a complementary approach that may help to provide a better understanding of results obtained in vivo. (C) 2010 Elsevier B.V. All rights reserved.