Refining in vitro digestibility assays: Fractionation of digestible and indigestible peptides1 (original) (raw)

2004, Journal of Animal Science

Typically, in vitro methods used for estimating the amount of ileal digestible AA do not exhaustively digest samples, and arbitrary methods for separating digestible from indigestible protein are used. This may lead to over-or underestimation of digestibility coefficients. A method that exhaustively digests proteins using pepsin and pancreatin was developed, and the first objective of this research was to confirm that exhaustive digestion was indeed appropriate and to determine the fractionation method for separating digestible from indigestible proteins. For this, three homoarginine-labeled animal proteins were prepared. Samples were subsequently digested in vivo and in vitro to determine which fraction should be considered indigestible, and in vitro followed by in vivo to determine whether the extent of digestion in vivo was improved by predigestion. In vivo, soluble but unabsorbed peptides were smaller than 1 kDa, suggesting that the size of soluble peptides is not what prevents their absorption. Thus, all in vitro-soluble proteins should be considered digestible. In vitro, 88 ± 3% of the soluble peptides were smaller than 1 kDa, with the remainder between 1 and 5 kDa, suggesting that in

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