True Ileal Amino Acid Digestibility and Protein Quality of 15N-Labeled Faba Bean in Healthy Humans.

BACKGROUND: The recommended transition toward more plant-based diets, particularly containing legumes, requires a wider knowledge of plant protein bioavailability. Faba beans are cultivated at different latitudes and are used increasingly in human nutrition. OBJECTIVES: We aimed to assess the nutritional quality of faba bean protein in healthy volunteers equipped with an intestinal tube to implement the ileal 15N balance method. METHODS: Nine volunteers completed the study (7 males, 2 females, aged 33 ± 10 y, BMI: 24.7 ± 2.6 kg/m2). They were equipped with a nasoileal tube. After fasting overnight, they ingested a test meal consisting of cooked mash of dehulled faba bean seeds (20 g protein per serving of approximately 250 g) intrinsically labeled with 15N. Samples of ileal contents, plasma, and urine were collected over an 8-h postprandial period. Undigested nitrogen (N) and amino acids (AAs) were determined using isotopic MS, and subsequently, ileal digestibility and digestible indispensable amino acid score (DIAAS) were calculated. The measurement of postprandial deamination allowed calculation of the net postprandial protein utilization (NPPU). RESULTS: The ileal N digestibility was 84.1% ± 7.7%. Postprandial deamination represented 19.2% ± 3.6% of ingested N, and the NPPU was 64.7% ± 9.7%. The ileal digestibility of individual AAs varied from 85.1% ± 13.7% for histidine to 94.2% ± 3.6% for glutamine + glutamate. The mean AA digestibility was ∼6 percentage points higher than the digestibility of N, reaching 89.8% ± 5.9%, whereas indispensable AA digestibility was 88.0% ± 7.3%. Histidine and tryptophan were the first limiting AAs [DIAAS = 0.77 (calculated by legume-specific N-to-protein conversion factor 5.4); 0.67 (by default factor 6.25)]. Sulfur AAs were limiting to a lesser extent [DIAA ratio = 0.94 (N × 5.4); 0.81 (N × 6.25)]. CONCLUSIONS: Protein ileal digestibility of cooked, dehulled faba beans in humans was moderate (<85%), but that of AAs was close to 90%. Overall protein quality was restricted by the limited histidine and tryptophan content. This trial was registered at clinicaltrials.gov as NCT05047757.

Differential effects of milk proteins on amino acid digestibility, post-prandial nitrogen utilization and intestinal peptide profiles in rats.

OBJECTIVE: The aim of this study was to analyze the protein digestibility and postprandial metabolism in rats of milk protein matrices obtained by different industrial processes. MATERIAL AND METHODS: The study was conducted on Wistar rats that consumed a meal containing different 15N-labeled milk proteins. Four milk matrices were tested: native micellar caseins (C1), caseins low in calcium (C2 low Ca2+), a matrix containing a ratio 63:37 of caseins and whey proteins (CW2) and whey proteins alone (W). Blood and urine were collected during the postprandial period and rats were euthanized 6 h after meal intake to collect digestive contents and organs. RESULTS: Orocaecal digestibility values of amino acids ranged between 96.0 ± 0.2% and 96.6 ± 0.4% for C1-, C2 low Ca2+- and W-matrices, while this value was significantly lower for CW2 matrix (92.4 ± 0.5%). More dietary nitrogen was sequestered in the splanchnic area (intestinal mucosa and liver) as well as in plasma proteins after ingestion of W matrix, especially compared to the C1- and C2 low Ca2+-matrices. Peptidomic analysis showed that more milk protein-derived peptides were identified in the caecum of rats after the ingestion of the matrices containing caseins compared to W matrix. CONCLUSION: We found that demineralization of micellar caseins did not modify its digestibility and postprandial metabolism. The low digestibility of the modified casein-to-whey ratio matrix may be ascribed to a lower accessibility of the protein to digestive enzymes due to changes in the protein structure, while the higher nitrogen splanchnic retention after ingestion of whey was probably due to the fast assimilation of its protein content. Finally, our results showed that industrial processes that modify the structure and/or composition of milk proteins influence protein digestion and utilization.

Digestive and metabolic bioavailability in healthy humans of 15N-labeled rapeseed and flaxseed protein incorporated in biscuits.

BACKGROUND: In the search to diversify protein sources for humans, oilseeds are good candidates due to the high protein content of their coproducts after oil extraction. Among them, rapeseed presents a well-balanced amino acid (AA) profile. Flaxseed is an emerging source but the nutritional value of its protein is not yet documented. OBJECTIVES: This study aimed to determine the nitrogen (N) and AA bioavailability of these protein sources. METHODS: Nineteen healthy volunteers were intubated with a naso-ileal tube. They ingested 156 g biscuits containing intrinsically labeled 15N rapeseed (n = 10) or flaxseed (n = 9) protein over a 4-h period. Ileal digesta, blood, and urine were sampled over 8 h after the first meal ingestion. N and 15N enrichment and AAs were measured to determine digestive and deamination losses. Ileal digestibility, the digestible indispensable AA score (DIAAS) and net postprandial protein utilization (NPPU) were calculated. RESULTS: Real ileal digestibility was 80.7 ± 6.5% for rapeseed protein and 92.2 ± 2.0% for flaxseed protein (P = 0.0002). Mean indispensable AA (IAA) digestibility reached 84.1 ± 6.9% and 93.3 ± 6.7% for rapeseed and flaxseed, respectively, lysine being the lowest digestible IAA for both sources. Despite moderate digestibility, the DIAAS was 1.1 for rapeseed but only 0.6 for flaxseed due to lysine insufficiency. Deamination losses accounted for 20.0 ± 6.5% of dietary N for flaxseed and 11.0 ± 2.8% for rapeseed (P = 0.002). The NPPU did not differ between the protein sources, with 71.3 ± 6.5% for flaxseed and 69.7 ± 7.6% for rapeseed. CONCLUSIONS: Despite good digestibility, flaxseed protein cooked in biscuits was penalized by both lysine insufficiency and poor lysine digestibility that decreased its DIAAS and increased deamination. By contrast, rapeseed was moderately digestible but presented no limiting IAA, resulting in an excellent DIAAS and low deamination. This study was registered at clinicaltrials.gov as NCT04024605.

Moderate adiposity levels counteract protein metabolism modifications associated with aging in rats.

PURPOSE: Physiological parameters such as adiposity and age are likely to influence protein digestion and utilization. The aim of this study was to evaluate the combined effects of age and adiposity on casein protein and amino acid true digestibility and its postprandial utilization in rats. METHODS: Four groups were included (n = 7/8): 2 months/normal adiposity, 2 months/high adiposity, 11 months/normal adiposity and 11 months/high adiposity. Rats were given a calibrated meal containing 15N-labeled casein (Ingredia, Arras, France) and were euthanized 6 h later. Digestive contents were collected to assess protein and amino acid digestibilities. 15N enrichments were measured in plasma and urine to determine total body deamination. Fractional protein synthesis rate (FSR) was determined in different organs using a flooding dose of 13C valine. RESULTS: Nitrogen and amino acid true digestibility of casein was around 95-96% depending on the group and was increased by 1% in high adiposity rats (P = 0.04). Higher adiposity levels counteracted the increase in total body deamination (P = 0.03) that was associated with older age. Significant effects of age (P = 0.006) and adiposity (P = 0.002) were observed in the muscle FSR, with age decreasing it and adiposity increasing it. CONCLUSION: This study revealed that a higher level of adiposity resulted in a slight increase in protein and individual amino acid true digestibility values and seemed to compensate for the metabolic postprandial protein alterations observed at older age.