Sequential release of milk protein–derived bioactive peptides in the jejunum in healthy humans

Abstract

Background:The digestive hydrolysis of dietary proteins leads to the release of peptides in the intestinal tract, where they may exert a variety of functions, but their characterization and quantification are difficult. Objectives: We aimed to characterize and determine kinetics of the formation of peptides present in the jejunum of humans who ingested casein or whey proteins by using mass spectrometry and to look for and quantify bioactive peptides. Design: Subjects were equipped with a double-lumen nasogastric tube that migrated to the proximal jejunum. A sample collection was performed for 6 h after the ingestion of 30 g 15 N-labeled casein (n = 7) or whey proteins (WPs; n = 6). Nitrogen flow rates were measured, and peptides were identified by using mass spectrometry. Results: After casein ingestion, medium-size peptides (750-1050 kDa) were released during 6 h, whereas larger peptides (1050-1800 kDa) were released from WPs in the first 3 h. A total of 356 and 146 peptides were detected and sequenced in the jejunum after casein and WP ingestion, respectively. b-casein was the most important precursor of peptides, including bioactive peptides with various activities. The amounts of b-casomorphins (b-casein 57-, 58-, 59-, and 60-66) and b-casein 108-113 released on the postprandial window were sufficient to elicit the biological action of these peptides (ie, opioid and antihypertensive, respectively). Conclusions: Clear evidence is shown of the presence of bioactive peptides in the jejunum of healthy humans who ingested casein. Our findings raise the question about the physiologic conditions under which these peptides can express their bioactivity in humans. This trial was registered at clinicaltrials.gov as NCT00862329.Am J Clin Nutr 2013;97:1314-23.

Milk proteins as a source of tryptophan-containing bioactive peptides

“…In general, the peptides which were predicted in silico to be released by GI enzymes (Table 2) have not been identified in the GIT (Table 3). However, 50 larger β-CN peptides predicted to be released in silico (Table 2) may act as precursors of the five β-CN derived W-containing peptides which has been identified in the jejunal contents of humans 32 . These peptide precursors may be further cleaved by carboxy-and aminopeptidases present in the GIT of humans 39,40 .…”

Avances en el conocimiento de las proteínas de la leche materna

“…Por ejemplo, la mucosa gástrica de estos recién nacidos secreta niveles bajos de ácido clorhídrico, lo que posibilita que el pH gástri-co postprandial llegue a valores cercanos al neutro; el pH más alto disminuye la activación de la pepsina y la actividad antimicrobiana del jugo gástrico 28 . La mayor velocidad de vaciamiento de las proteínas parcialmente hidrolizadas es una ventaja porque permite el descenso del pH y el retorno de la actividad bactericida en el lumen gástrico 9,11 . La enteroquinasa es sintetizada por los enterocitos del duodeno y activa al tripsinógeno, el quimotripsinógeno y la proelastasa y a otras proteasas pancreáticas a sus formas activas 28 .…”

Protein metabolism and physical training: any need for amino acid supplementation?

“…b) Milk and derivatives As a point of view, full or skimmed milk contains two major types of proteins: casein and whey proteins (milk without casein). It appears that whey proteins are faster (twice) rejected from the stomach into the duodenum as compared to casein [130][131][132][133] increasing therefore food availability during muscle exercise. As well, Burke et al observed that whey protein ingestion induced a faster inclusion within plasma volume as compared to whole milk [44].…”