Protein Ingredient Quality within Infant Formulas Impacts Plasma Amino Acid Concentrations in Neonatal Minipiglets.

BACKGROUND: Infant formulas (IFs), the only adequate substitute to human milk, are complex matrices that require numerous ingredients and processing steps that may impact protein digestion and subsequent amino acid (AA) absorption. OBJECTIVES: The objective was to understand the impact of the protein ingredient quality within IFs on postprandial plasma AA profiles. METHODS: Four isonitrogenous and isocaloric IFs were produced at a semi-industrial scale using whey proteins from different origins (cheese compared with ideal whey) and denaturation levels (IF-A, -B, -C), and caseins with different supramolecular organizations (IF-C, -D). Ten Yucatan minipiglets (12- to 27-d-old) were used as a human infant model and received each IF for 3 d according to a Williams Latin square followed by a 2-d wash-out period. Jugular plasma was regularly sampled from 10 min preprandial to 4 h postprandial on the third day to measure free AAs, urea, insulin, and glucose concentrations. Data were statistically analyzed using a mixed linear model with diet (IFs), time, and sex as fixed factors and piglet as random factor. RESULTS: IFs made with cheese whey (IF-A and -B) elicited significantly higher plasma total and essential AA concentrations than IFs made with ideal whey (IF-C and -D), regardless of the pre- and postprandial times. Most of the differences observed postprandially were explained by AA homeostasis modifications. IFs based on cheese whey induced an increased plasma concentration of Thr due to both a higher Thr content in these IFs and a Thr-limiting degrading capability in piglets. The use of a nonmicellar casein ingredient led to reduced plasma content of AA catabolism markers (IF-D compared with IF-C). CONCLUSIONS: Overall, our results highlight the importance of the protein ingredient quality (composition and structure) within IFs on neonatal plasma AA profiles, which may further impact infant protein metabolism.

The use of 15N-labelled protein to account for the endogenous nitrogen contribution to in vitro protein digestibility measurement.

Protein digestibility, a key indicator of dietary protein quality for human nutrition, can be estimated using an in vitro digestion model, however its definition and determination remain variable across studies. The present study aimed to determine the contribution of the endogenous nitrogen (N) to the plant and animal protein digestibility values obtained in vitro. 15N-labelled gluten and caseins (4, 8 and 16 % of the model meal) were used to differentiate dietary and endogenous N and were digested using the INFOGEST in vitro digestion model with no oral phase. The dietary and endogenous N were measured before and during digestion after centrifugation and 10 kDa ultrafiltration. The proteolysis degree was measured by the OPA method. The endogenous and dietary N were determined by elemental analyser coupled with isotopic ratio mass spectrometry. Apparent and true digestibility were determined and values of 135, 92 and 71 % for apparent vs. 78, 69, 60 % for true digestibility were obtained for 4, 8 and 16 % dietary protein level, respectively, with a significant effect of protein level. Differences between apparent and true digestibility pointed out the important contribution of the endogenous nitrogen. Our results showed that 40 % of the N below 10 kDa, i.e., the digestible fraction, were from endogenous origin (i.e. from the pancreatin) and was even present before digestion. An average value of 27 % for pancreatin N autolysis was estimated independently of the protein levels or sources. The use of 15N-labelled protein to evaluate in vitro protein digestibility highlighted the important contribution of the endogenous N, in particular when low dietary protein solution (4 %) are digested. This gives new keys to overcome drawbacks of in vitro models for determining protein digestibility.

Protein ingredient quality of infant formulas impacts their structure and kinetics of proteolysis under in vitro dynamic digestion.

Infant formula (IF) is a complex matrix requiring numerous ingredients and processing steps. The objective was to understand how the quality of protein ingredients impacts IF structure and, in turn, their kinetics of digestion. Four powdered IFs (A/B/C/D), based on commercial whey protein (WP) ingredients, with different protein denaturation levels and composition (A/B/C), and on caseins with different supramolecular organisations (C/D), were produced at a semi-industrial level after homogenization and spray-drying. Once reconstituted in water (13 %, wt/wt), the IF microstructure was analysed with asymmetrical flow field-flow fractionation coupled with multi-angle light scattering and differential refractometer, transmission electron microscopy and electrophoresis. The rehydrated IFs were subjected to simulated infant in vitro dynamic digestion (DIDGI®). Digesta were regularly sampled to follow structural changes (confocal microscopy, laser-light scattering) and proteolysis (OPA, SDS-PAGE, LC-MS/MS, cation-exchange chromatography). Before digestion, different microstructures were observed among IFs. IF-A, characterized by more denatured WPs, presented star-shaped mixed aggregates, with protein aggregates bounded to casein micelles, themselves adsorbed at the fat droplet interface. Non-micellar caseins, brought by non-micellar casein powder (IF-D) underwent rearrangement and aggregation at the interface of flocculated fat droplets, leading to a largely different microstructure of IF emulsion, with large aggregates of lipids and proteins. During digestion, IF-A more digested (degree of proteolysis + 16 %) at 180 min of intestinal phase than IF-C/D. The modification of the supramolecular organisation of caseins implied different kinetics of peptide release derived from caseins during the gastric phase (more abundant at G80 for IF-D). Bioactive peptide release kinetics were also different during digestion with IF-C presenting a maximal abundance for a large proportion of them. Overall, the present study highlights the importance of the structure and composition of the protein ingredients (WPs and caseins) selected for IF formulation on the final IF structure and, in turn, on proteolysis. Whether it has some physiological consequences remains to be investigated.

Specific joint angle dependency of voluntary activation during eccentric knee extensions.

INTRODUCTION: This study compared voluntary activation during isometric, concentric, and eccentric maximal knee extensions at different joint angles. METHODS: Fifteen participants performed isometric, concentric, and eccentric protocols (9 contractions each). For each protocol, the central activation ratio (CAR) was randomly measured at 50°, 75°, or 100° of knee joint angle (0° = full knee extension) using superimposed supramaximal paired nerve stimulations during contractions. RESULTS: CAR increased between 50° and 100° during isometric (93.6 ± 3.1 vs. 98.5 ± 1.4%), concentric (92.4 ± 5.4 vs. 99.2 ± 1.2%), and eccentric (93.0 ± 3.5 vs. 96.6 ± 3.8%) contractions. CAR was lower during eccentric than both isometric and concentric contractions at 75° and 100°, but similar between contraction types at 50°. CONCLUSIONS: The ability to activate muscle maximally is impaired during eccentric contractions compared with other contraction types at 75° and 100°, but not at 50°. Muscle Nerve 56: 750-758, 2017.