Poster Topical Area: Energy and Macronutrient Metabolism
Location: Hall D
Poster Board Number: 522
Objectives: Bioavailability of indispensable amino acids (AA) is a determinant factor of protein quality. The intrinsic labeling of dietary proteins with 15N is usually used to determine the digestive fate of IAA but cannot be applied to all protein sources. Deuterated water is an alternative but its accuracy has not been assessed. We aimed to compare the performance of 15N and 2H for determination of protein digestibility and AA bioavailability.
Methods: Milk was labelled from 4 goats receiving orally 5g of 15N ammonium sulfate (99 %). Eighty or 160 ml 2H2O (98 %) was given in drinking water for 1 or 3 days and milk was collected. Proteins were purified from milk and their 15N and 2H enrichments determined. Protein digestibility and AA bioavailability was assessed in 6 rats receiving a single test meal. Dietary proteins and AA were quantified in gastrointestinal segments by EA-IRMS and GC-C-IRMS respectively.
Results: 15N enrichment was 1.00 ± 0.07 % in milk proteins and the AA showed a uniform 15N enrichment of 0.94 ± 0.11 % on average. The best 2H enrichment in milk proteins (0.18 %) was obtained with the highest dose of 2H2O administered during 3 days. In contrast to 15N, 2H enrichment in milk IAA was not uniform, varying from 0.03 % for phenylalanine to 0.11 % for proline. In vivo, no 2H enrichment was found in the colon contrary to 15N, leading to a slightly higher orofaecal protein digestibility when assessed with 2H (98.0 ± 0.1 % for 2H vs 97.6 ± 0.1 % for 15N, P = 0.0004). However, orocaecal protein digestibility was similar with both tracers. With 15N labelling, the mean AA bioavailability of milk was estimated to be 98.0±0,3%, varying from 95.8 ± 1,6 % (valine) to 99.1 ± 0.3 % (methionine and lysine). The mean AA bioavailability determined with 2H was significantly lower than determined with 15N (96.0 ± 0.8 %, P = 0.0006) and varied from 80.3 ± 2.4 % (threonine) to 98.7 ± 0.4 % (methionine).
Conclusions: Deuterium labeling of dietary protein appears as convenient as 15N to follow the digestive fate of proteins. However, AA bioavailability seems to be underestimated with 2H compared to 15N. Differences in caecum and colon bacterial metabolism as well as transamination of hydrogen exchange mechanisms may partly explained these discrepancies.
AgroParistech, UMR PNCA, INRA, AgroParisTech, Université Paris-Saclay, Paris, France
Paris, Ile-de-France, France