Casein Protein Processing Strongly Modulates Post-Prandial Plasma Amino Acid Responses In Vivo in Humans

Abstract

Micellar casein is characterized as a slowly digestible protein source, and its structure can be modulated by various food processing techniques to modify its functional properties. However, little is known about the impact of such modifications on casein protein digestion and amino acid absorption kinetics and the subsequent post-prandial plasma amino acid responses. In the present study, we determined post-prandial aminoacidemia following ingestion of isonitrogenous amounts of casein protein (40 g) provided as micellar casein (Mi-CAS), calcium caseinate (Ca-CAS), or cross-linked sodium caseinate (XL-CAS). Fifteen healthy, young men (age: 26 ± 4 years, BMI: 23 ± 1 kg·m−2) participated in this randomized cross-over study and ingested 40 g Mi-Cas, Ca-CAS, and XL-CAS protein, with a ~1 week washout between treatments. On each trial day, arterialized blood samples were collected at regular intervals during a 6 h post-prandial period to assess plasma amino acid concentrations using ultra-performance liquid chromatography. Plasma amino acid concentrations were higher following the ingestion of XL-CAS when compared to Mi-CAS and Ca-CAS from t = 15 to 90 min (all p < 0.05). Plasma amino acid concentrations were higher following ingestion of Mi-CAS compared to Ca-CAS from t = 30 to 45 min (both p < 0.05). Plasma total amino acids iAUC were higher following the ingestion of XL-CAS when compared to Ca-CAS (294 ± 63 vs. 260 ± 75 mmol·L−1, p = 0.006), with intermediate values following Mi-CAS ingestion (270 ± 63 mmol·L−1, p > 0.05). In conclusion, cross-linked sodium caseinate is more rapidly digested when compared to micellar casein and calcium caseinate. Protein processing can strongly modulate the post-prandial rise in plasma amino acid bioavailability in vivo in humans.

Assessing the whole-body protein synthetic response to feeding in vivo in human subjects

“…Exogenous rates of appearance are sometimes estimated based on literature values (36) . However, exogenous rates of amino acid appearance are highly dependent on experimental context such as the dose of ingested amino acids, nutrient co-ingestion, (prior) exercise, age and the presence or absence of disease (37)(38)(39)(40)(41) . Any deviation from the experimental conditions under literature values for the exogenous rate of appearance were established will introduce error in the estimation.…”

A controlled human intervention trial to study protein quality by amino acid uptake kinetics with the novel Lemna protein concentrate as case study

“…It has to be said that postprandial plasma amino acids levels are a result of processes in the body and therefore amino acids might not only be low because of resistance towards intestinal enzymes and low bioavailability, but also due to fast metabolisation. A (dual) tracer approach to measuring in vivo protein quality will be more accurate (Edwards et al 2002;Gaudichon et al 2002;Trommelen et al 2020) but also more costly and measuring ileal digestibility in patients with an ileostomy (Moughan et al 2005) presents its challenges and will be difficult to implement as standardised protocol worldwide.…”

“…The most reliable methods to analyse protein digestion in humans make use of labelling strategies (Edwards et al 2002;Gaudichon et al 2002;Trommelen et al 2020), but these methods are costly and cannot easily be implemented as standard protocol worldwide. Measuring the appearance of postprandial amino acids levels is relatively easy to perform and is already used by many science groups all over the world.…”

Comprehensive assessment of post-prandial protein handling by the application of intrinsically labelled protein in vivo in human subjects

“…Dietary protein-derived amino acid release into the circulation is preceded by a series of complex processes, including mastication, gastric mixing, gastric emptying into the intestine, protein cleavage into amino acids, diand tri-peptides, transport into the enterocytes, amino acid extraction by splanchnic tissues and the release of the remaining dietary protein-derived amino acids into the circulation. The rise in circulating plasma amino acid concentrations is often used as a proxy of dietary protein digestion and amino acid absorption (21)(22)(23) . However, changes in plasma amino acid concentrations do not necessarily reflect the mere appearance rate of exogenous (dietary protein-derived) amino acids as they are also impacted by changes in the release of amino acids originating from various tissues and the (rapid) uptake of amino acids in these tissues.…”

“…In contrast, maximal stimulation of fractional muscle protein synthesis rates seems to occur at an ingested dose of about 20-30 g dietary protein (6,25,59,60) . Ingestion of greater dosages of intrinsically labelled protein further increases dietary protein-derived amino acid incorporation into muscle tissue protein without a concomitant increase muscle protein synthesis rate (21,27,51) . This is the direct result of a greater post-prandial release of labelled amino acids and, as such, greater post-prandial precursor availability derived from the ingested protein source.…”