Abstract
Whey protein is generally found to be faster digested and to promote faster and higher increases in plasma amino acid concentrations during the immediate ~60 min following protein ingestion compared to casein. The aim of the present study was to compare three different whey protein hydrolysates with varying degrees of hydrolysis (DH, % cleaved peptide bonds) to evaluate if the degree of whey protein hydrolysis influences the rate of amino acid plasma appearance in humans. A casein protein was included as reference. The three differentially hydrolysed whey proteins investigated were: High degree of hydrolysis (DH, DH = 48 %), Medium DH (DH = 27 %), and Low DH (DH = 23 %). The casein protein was intact. Additionally, since manufacturing of protein products may render some amino acids unavailable for utilisation in the body the digestibility and the biological value of all four protein fractions were evaluated in a rat study. A two-compartment model for the description of the postprandial plasma amino acid kinetics was applied to investigate the rate of postprandial total amino acid plasma appearance of the four protein products. The plasma amino acid appearance rates of the three whey protein hydrolysates (WPH) were all significantly higher than for the casein protein, however, the degree of hydrolysis of the WPH products did not influence plasma total amino acid appearance rate (estimates of DH and 95 % confidence intervals [CI] (mol L−1 min−1): High DH 0.0585 [0.0454, 0.0754], Medium DH 0.0594 [0.0495, 0.0768], Low DH 0.0560 [0.0429, 0.0732], Casein 0.0194 [0.0129, 0.0291]). The four protein products were all highly digestible, while the biological value decreased with increasing degree of hydrolysis. In conclusion, the current study does not provide evidence that the degree of whey protein hydrolysis is a strong determinant for plasma amino acid appearance rate within the studied range of hydrolysis and protein dose.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-1995-x) contains supplementary material, which is available to authorized users.
Highlights
Maintenance of skeletal muscle mass and function throughout life is essential for mobility, healthy living and quality of life
We found that a two compartment kinetic model, where the plasma appearance was assumed to be of zeroth order and the plasma clearance was assumed to be of first order, fitted well with the time course of the measured plasma amino acid concentrations for each subject following ingestion of each drink
We found that the degree of hydrolysis does not seem to constitute a pivotal factor for the postprandial rate of amino acid appearance of whey protein hydrolysates within the studied range of hydrolysis
Summary
Maintenance of skeletal muscle mass and function throughout life is essential for mobility, healthy living and quality of life. The essential amino acids (EAAs) in a protein supplement are primarily responsible for stimulation of MPS following protein ingestion (Tipton et al 1999b; Volpi et al 2003). In this regard, the amino acid induced stimulation of MPS in the rested state has been found to increase in a dose-dependent manner until a threshold of approximately 10 g of EAA is reached, whereas no further increase in MPS is observed with 20 or 40 g of EAA (Cuthbertson et al 2005). Absence of leucine in an EAA supplement, has been observed to reduce activation of mTOR signalling which potentially could reduce the MPS (Moberg et al 2014). The latter observation has given rise to the suggestion that leucine may be a MPS “trigger” so that protein supplements rich in leucine would be more effective at stimulating MPS than supplements with a lower leucine content (Phillips 2014)
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