Very low ileal nitrogen and amino acid digestibility of zein compared to whey protein isolate in healthy volunteers
The American Journal of Clinical Nutrition. 2021-01-01; 113(1): 70-82
DOI: 10.1093/ajcn/nqaa274
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Calvez J(1), Benoit S(1), Piedcoq J(1), Khodorova N(1), Azzout-Marniche D(1), Tomé D(1), Benamouzig R(1), Airinei G(1), Gaudichon C(1).
Author information:
(1)Université Paris-Saclay, AgroParisTech, National Research Institute for
Agriculture, Food and Environment (INRAE), Nutrition Physiology and Ingestive
Behavior UMR (unité mixte de recherche) (UMR PNCA), Paris, France.
BACKGROUND: Whey protein and zein are of nutritional interest due to their high
leucine content, but little data are available on their amino acid (AA) ileal
digestibility.
OBJECTIVE: This study aimed to determine ileal digestibility of whey protein
isolate (WPI) and zein in healthy volunteers by use of the naso-ileal intubation
method, which allows continuous collection of postprandial ileal digesta.
METHODS: Twenty-two healthy volunteers were intubated with a naso-ileal sampling
device positioned at the terminal ileum level. They received a single meal of
protein-free biscuits and a drink containing zein (n = 8), WPI (n = 7), or no
protein (protein free, n = 7). Ileal effluents and plasma samples were collected
over a 9-h postprandial period. Total nitrogen and AA contents were quantified
in effluents. True ileal digestibility was calculated after correction for
endogenous losses evaluated in the protein-free group.
RESULTS: True ileal nitrogen digestibility of zein was markedly lower than WPI
(60.2 ± 4.5% and 91.2 ± 2.6%, respectively, P = 0.0003). True ileal
digestibility of AAs ranged from 87.4 ± 2.7% for threonine to 98.4 ± 1.0% for
methionine in the WPI group, and from 59.3 ± 5.6% for methionine to 69.0 ± 5.8%
for arginine in the zein group. The digestible indispensable AA (IAA) score was
1.03 (histidine) for WPI and close to 0 for zein, owing to its negligible lysine
content. Plasma IAA concentration significantly increased after WPI intake
(P = 0.0319), whereas no effect of zein on aminoacidemia was observed, including
plasma leucine, despite its high leucine content.
CONCLUSIONS: Our findings provide data on ileal digestibility of WPI and zein
AAs in healthy humans and, in contrast to WPI, zein is poorly digestible. This
study was registered at clinicaltrials.gov as NCT03279211.
© The Author(s) 2020. Published by Oxford University Press on behalf of the
American Society for Nutrition.
DOI: 10.1093/ajcn/nqaa274
PMID: 33021640