During ageing, skeletal muscle develops anabolic resistance towards the stimulation of protein synthesis induced by dietary amino acids. The stimulation of muscle protein synthesis after food intake remains insufficient, even with a protein intake recommended for healthy adults. This alteration is one of the mechanisms known to be responsible for the decrease of muscle mass and function during ageing, namely sarcopenia. Increasing dietary protein intake above the current RDA(0⋅83 g/kg/d) has been strongly suggested to overcome the anabolic resistance observed. It is also specified that the dietary protein ingested should be of good quality. A protein of good quality is a protein whose amino acid (AA) composition covers the requirement of each AA when ingested at the RDA. However, the biological value of proteins may vary among dietary sources in which AA composition could be unbalanced. In the present review, we suggest that the quality of a dietary protein is also related to several other determinants. These determinants include the speed of digestion of dietary proteins, the presence of specific AA, the food matrix in which the dietary proteins are included, the processes involved in the production of food products (milk gelation and cooking temperature), the energy supply and its nature, and the interaction between nutrients before ingestion. Particular attention is given to plant proteins for nutrition of the elderly. Finally, the timing of protein intake and its association with the desynchronized intake of energetic nutrients are discussed.

Food matrix is known to interact with some dietary constituents and microconstituents during digestion. These interactions may potentially affect the metabolism and bioavailability of some compounds, and as a consequence modulate their biological effects. In this context, the aim of this study was to determine the effect of apple food matrix on the bioavailability of flavan-3-ols and on the ability of these compounds to modulate the nutrigenomic response to a high fat challenge in minipigs.

Adult male Yucatan minipigs (n = 5) were assigned to a random treatment sequence of high-fat meals non supplemented or supplemented with 250 g of raw apple, 250 g of apple puree or 1.4 g of apple polyphenols extract, with a 7-days washout period between each treatment. Each supplementation provided 155 mg flavan-3-ol monomers. At each treatment period, fasting- and 1h-, 2h-, 3h-postprandial blood samples were collected, and the concentration in flavan-3-ol monomers was measured on hydrolyzed serum, using UPLC-Q-TOF MS. The ability of apple-derived products to modulate the postprandial gene expression profile was assessed and compared in circulating PBMCs collected at 3 h after consumption of the four tested meals using a microarray analysis.

Results show that the apple matrix did not affect the kinetic of the postprandial absorption of flavan-3-ol monomers. The total flavan-3-ols concentrations measured at peak were significantly higher in the extract (x1.75), suggesting an impact of the apple matrix on flavan-3-ols absorption. However, no significant difference in total flavanols was observed between raw apple and apple puree.

Principal Component Analysis of the microarray data from PBMCs identified three distinct clusters of gene expression patterns: one corresponding to gene expression profiles after the high-fat meal, one for meal supplemented with raw apples or apple puree, and a third cluster for meal supplemented with polyphenol extract. A set of 309 genes was identified as differentially expressed by apple-derived products compared to high-fat meal alone, including 93 modulated with the three apple products. The variations in gene expression were similar for only 75% of the 93 genes, suggesting that the apple matrix affects the nutrigenomic response to flavan-3-ols. A bioinformatics analysis revealed that genes affected by apple-derived products are involved in inflammation and leukocyte transendothelial migration, suggesting a beneficial impact of apple-derived products.

In conclusion, these results raise awareness for considering the impact of food matrix on the biological responsiveness of polyphenols in future nutritional studies.

Cysteine (Cys), a conditionally indispensable amino acid, is required for the detoxification of paracetamol (acetaminophen, N-acetyl-para-aminophenol, 4-hydroxy-acetanilide, APAP), a drug of widespread use in older persons. We recently reported that repeated APAP cures could worsen sarcopenia in old rats, likely to be due to the impairment of Cys/GSH homoeostasis. The aim of the study was to evaluate whether a dietary Cys supplementation during APAP cures could improve Cys/GSH homoeostasis and thus preserve skeletal muscle. Male 21·5-month-old Wistar rats received three 2-week-long cures of APAP (1 % of diet) alone or with extra Cys (0·5 % of diet), intercalated with washout periods of 2 weeks (APAP and APAP–Cys groups, respectively). They were compared with untreated control rats (CT group). CT and APAP–Cys groups were pair-fed to the APAP group. Dietary Cys supplementation was efficient to prevent increase in liver mass (P<0·0001), decrease in liver GSH (P<0·0001), increase in blood GSH concentration (P<0·0001), and to some extent, decrease in plasma free Cys concentration (P<0·05), all induced by repeated APAP cures. The addition of Cys to APAP cures decreased plasma alanine transaminase (P<0·05), the fractional synthesis rate of liver proteins (P<0·01), and increased masses of extensor digitorum longus (P<0·01), and soleus (P<0·05), compared with the APAP group. Cys supplementation prevented alteration in Cys/GSH homoeostasis and increased some muscle masses in old rats under repeated cures with a non-toxic dose of APAP.

Digestive kinetics are believed to modulate satiety through the modulation of nutrient delivery. We hypothesised that the duration of satiety could be extended by modulating the kinetics of dietary amino acid delivery in overweight subjects, using snacks containing casein and whey protein. In the present study, eighty-two subjects underwent a first satiety test where they received a control snack containing 60 g maltodextrin. For the next 5 d, the subjects consumed a liquid protein snack containing 30 g carbohydrates and 30 g proteins (casein, whey protein or an equal mix of the two; n 26–28 per group). The subjects then underwent a second satiety test after ingesting the protein snack. The time period elapsing between the snack and request for lunch, food intake at lunch and satiety scores were recorded. A subgroup of twenty-four subjects underwent a digestive and metabolic investigation after ingesting their protein snack. Gastric emptying times were 2·5, 4 and 6 h for whey protein, mix and casein, respectively, displaying different kinetics of appearance of dietary N in plasma but without affecting pancreatic and gastrointestinal hormones. Compared with the control snack, proteins extended the duration of satiety (+17 min, P= 0·02), with no difference between the protein groups. The satiating effect of proteins was greater in subjects who ate their lunch early after the snack (below the median value, i.e. 2 h) at the control test (+32 min, P= 0·001). Energy intake at lunch was not modulated by proteins. The satiating effect of proteins is efficient in overweight subjects, especially when the duration of satiety is short, but independently of their digestive and plasma amino acid kinetics.

Periods of immobilisation are often associated with pathologies and/or ageing. These periods of muscle disuse induce muscle atrophy which could worsen the pathology or elderly frailty. If muscle mass loss has positive effects in the short term, a sustained/uncontrolled muscle mass loss is deleterious for health. Muscle mass recovery following immobilisation-induced atrophy could be critical, particularly when it is uncompleted as observed during ageing. Exercise, the best way to recover muscle mass, is not always applicable. So, other approaches such as nutritional strategies are needed to limit muscle wasting and to improve muscle mass recovery in such situations. The present review discusses mechanisms involved in muscle atrophy following disuse and during recovery and emphasises the effect of age in these mechanisms. In addition, the efficiency of nutritional strategies proposed to limit muscle mass loss during disuse and to improve protein gain during recovery (leucine supplementation, whey proteins, antioxidants and anti-inflammatory compounds, energy intake) is also discussed.

For a controlled structure, the changes of physical characteristics like natural frequencies, modal damping coefficients, and what’s more on mode shapes will destabilize the controlled system. To keep the control performance and guarantee its robustness, a new modal control method using real-time identification is proposed to overcome the instability of controlled structure, especially induced by the inversion of mode shape. In this paper, a modal model of time-varying mechanical structure is supplied by an identifier. The choice of the kind of control permits to use this time-varying model for optimizing and self-adapting the controller. In order to supply the controller, a modal observer is used and also updated. For illustrative purpose, this proposed methodology is carried out on a simple but representative time-varying mechanical structure. On this example, an inertia modification leads not only to low modal frequency shifts but also to inversion of a mode shape. This mode shape inversion is shown to destabilize the controlled structure when the control system is not updated. The overall procedure will be described through simulations and performed for different operating conditions, which will prove that mode shapes have to be precisely determined and updated in the controller and observer to guarantee a robust modal control with high performances in spite of the changes of structure.

Extrusion is used to decrease leguminous seed protein degradability in the rumen in order to shift part of the dietary protein digestion towards the small intestine. The effect of such displacement of digestion site on the partitioning of nutrient net fluxes across the gastrointestinal tract was studied using four sheep fitted with catheters and blood-flow probes, allowing measurements across the rumen, the mesenteric-drained viscera (MDV) and the portal-drained viscera (PDV). Two diets containing 34 % of pea seeds were tested in a crossover design. They differed only according to pea treatment: raw pea (RP) or extruded pea (EP) diet. Rumen undegradable protein (RUP) accounted for 23 and 40 % of dietary crude protein for RP and EP diets, respectively. Across the rumen wall, ammonia net flux was lower with EP diet, whereas urea net flux was not different. Across the MDV, free amino acid (FAA) net flux was greater with EP diet, whereas peptide amino acid net flux was not different, accounting for 7 % of the non-protein amino acid net release. From RP to EP diet, PDV net flux of ammonia decreased by 23 %, whereas FAA net release increased by 21 %. The difference in dietary RUP did not affect the PDV net flux of SCFA, 3-hydroxybutyrate, lactate and glucose. In conclusion, the partial shift in pea protein digestion from the rumen to the small intestine did not affect the portal net balance of N, but decreased N loss from the rumen, and increased amino acid intestinal absorption and portal delivery.

The aim of the present study was to determine whether the addition of soluble fibre in the diet affected protein metabolism in the intestinal tissues, some visceral organs and in skeletal muscle. A diet supplemented with pectin (80 g/kg) was fed to young growing rats and the effect on organ mass and protein metabolism in liver, spleen, small and large intestines and gastrocnemius muscle was monitored and compared with the control group. Protein synthesis rates were determined by measuring [13C]valine incorporation in tissue protein. In the pectin-fed rats compared with the controls, DM intake and body weight gain were reduced (9 and 20 %, respectively) as well as gastrocnemius muscle, liver and spleen weights (6, 14 and 11 %, respectively), but the intestinal tissues were increased (64 %). In the intestinal tissues all protein metabolism parameters (protein and RNA content, protein synthesis rate and translational efficiency) were increased in the pectin group. In liver the translational efficiency was also increased, whereas its protein and RNA contents were reduced in the pectin group. In gastrocnemius muscle, protein content, fractional and absolute protein synthesis rates and translational efficiency were lower in the pectin group. The stimulation of protein turnover in intestines and liver by soluble fibre such as pectins could be one of the factors that explain the decrease in muscle turnover and whole-body growth rate.

Characterisation and identification of peptides (800 to 5000 Da) generated by intestinal digestion of fish or meat were performed using MS analyses (matrix-assisted laser desorption ionisation time of flight and nano-liquid chromatography electrospray-ionisation ion trap MS/MS). Four pigs fitted with cannulas at the duodenum and jejunum received a meal exclusively made of cooked Pectoralis profundus beef meat or cooked trout fillets. A protein-free meal, made of free amino acids, starch and fat, was used to identify peptides of endogenous origin. Peptides reproducibly detected in digesta (i.e. from at least three pigs) were evidenced predominantly in the first 3 h after the meal. In the duodenum, most of the fish- and meat-derived peptides were characteristic of a peptic digestion. In the jejunum, the majority of peptides appeared to result from digestion by chymotrypsin and trypsin. Despite slight differences in gastric emptying kinetics and overall peptide production, possibly in relation to food structure and texture, six and four similar peptides were released after ingestion of fish or meat in the duodenum and jejunum. A total of twenty-six different peptides were identified in digesta. All were fragments of major structural (actin, myosin) or sarcoplasmic (creatine kinase, glyceraldehyde-3-phosphate dehydrogenase and myoglobin) muscle proteins. Peptides were short ( < 2000 Da) and particularly rich in proline residues. Nineteen of them contained bioactive sequences corresponding mainly to an antihypertensive activity. The present work showed that after fish or meat ingestion, among the wide variety of peptides produced by enzymic digestion, some of them can be reproducibly observed in intestinal digesta.

Processing of maize grain is known to modulate the site of starch digestion, thus the nature and amount of nutrients delivered for absorption. We assessed the effect of site of starch digestion on nutrient net fluxes across portal-drained viscera (PDV). Three steers, fitted with permanent digestive cannulas and blood catheters, successively received two diets containing 35 % starch as dent maize grain. Diets differed according to maize presentation: dry and cracked (by-pass, BP) v. wet and ground (control, C). Ruminal physicochemical parameters were not significantly affected. Between C and BP, the decrease in ruminal starch digestion was compensated by an increase in starch digestion in the small intestine. The amount of glucose and soluble α-glucoside reaching the ileum was not affected. The amount of glucose disappearing in the small intestine increased from 238 to 531 g/d between C and BP, but portal net flux of glucose remained unchanged (−97 g/d). The portal O2 consumption and net energy release were not significantly affected, averaging 16 % and 57 % of metabolizable energy intake, respectively. The whole-body glucose appearance rate, measured by jugular infusion of [6, 6-2H2]glucose, averaged 916 g/d. The present study shows that the increase in the amount of glucose disappearing in the small intestine of conventionally fed cattle at a moderate intake level induces no change in portal net flux of glucose, reflecting an increase in glucose utilization by PDV. That could contribute to the low response of whole-body glucose appearance rate observed at this moderate level of intestinal glucose supply.

Digestion and portal net flux of nutrients were studied in sheep fed twice daily with fresh orchard-grass. Digestive flows were measured in six fistulated sheep using the double-marker technique. Three sheep were fitted with catheters and blood-flow probes, allowing nutrient net flux measurements across the portal-drained viscera (PDV), the mesenteric-drained viscera (MDV) and the rumen. Total tract apparent digestion of N was similar to portal net appearance of N, calculated as the sum of free amino acids (FAA), peptide amino acids (PAA), NH3, and urea net fluxes. PAA accounted for 25 % of non-protein amino acid net release across the PDV. With the exception of glycine and glutamate, the small intestine was the main contributor to this PAA net release. The essential amino acid (EAA) apparent disappearance between the duodenum and the ileum was lower than the net appearance of EAA (FAA + PAA) across the MDV. The value of PDV:MDV flux of free EAA was, on average, 78 %. The rumen accounted for 30 % of the net uptake of EAA by the PDV tissues not drained by the mesenteric vein. Rumen net release of acetate, propionate, butyrate, 3-hydroxybutyrate, and lactate accounted for 70, 55, 46, 77 and 52 %, respectively, of their portal net releases. Conversely, the small intestine was a net consumer of arterial acetate and 3-hydroxybutyrate. Dynamic study of nutrient net fluxes across the PDV showed that throughout a feeding cycle, the liver faced a constant flux of amino acids (AA), whereas volatile fatty acid and NH3 net fluxes varied in response to the meal. The present study specified, in forage-fed sheep, the partitioning of nutrient net fluxes across the PDV and the role of peptides in portal net release of AA.

In study 1, four cows had a ruminal canula, a catheter in the right ruminal vein and an ultrasonic flow probe around the right ruminal artery; a catheter was placed in the auricular artery on experimental days. Blood samples were taken every 10 min from -20 to 60 min after ruminal infusion of 5·79 mmol pteroylmonoglutamic acid and cyanocobalamin. There was a net release of these vitamins across the rumen wall following the infusion (P=0·06). In studies 2 and 3, four cows had catheters in the portal, one hepatic and two mesenteric veins and one mesenteric artery. Plasma flow was determined using p-aminohippurate. In study 2, blood samples were taken before and every 30 min for 6 h after feeding 0 or 4 mg of pteroylmonoglutamic acid. Flow of folates through the portal-drained viscera (PDV) and the total splanchnic tissues (TSP) tended to increase with the ingestion of pteroylmonoglutamic acid (P=0·19). In study 3, blood samples were collected every 30 min for the first 3 h to calculate plasma flow and basal net fluxes of folates and vitamin B12. The cows were fed 2·6 g pteroylmonoglutamic acid and 500 mg cyanocobalamin; blood samples were taken every 2 h for 24 h. Vitamin supplements increased the net release of folates and vitamin B12 from PDV (P=0·04) and TSP (P=0·13). The present results demonstrate that, in dairy cows, at doses reported to improve animal performance, passage of pteroylmonoglutamic acid to the portal blood appears during the 6 h following its ingestion, whereas for cyanocobalamin, it is a slow process, not yet completed 24 h after its ingestion.

We investigated whether short-term underfeeding could induce adaptative mechanisms in portal-drained viscera (PDV) that would allow nutrients to be spared for vital functions in adult ewes. Six ewes (three of them fitted with catheters in the mesenteric artery and portal and mesenteric veins) were fed, in a double 3×3 Latin square design (2 weeks per experimental period), a regrowth of natural grassland hay at 143 (high; H), 88 (medium; M) and 51 (low; L) % of their energy maintenance requirements. The digestibility of the diet was measured in all six ewes and the net portal fluxes of nutrients in the three catheterized ewes. The organic matter content and N digestibility of the diet were not affected by underfeeding. Urinary and faecal N losses and N balance were linearly related to feed intake. Arterial concentration of acetate was linearly related to feed intake. Arterial concentrations of the other volatile fatty acids, 3-hydroxybutyrate, lactate, glucose, NH3, urea and total amino acids were not affected by underfeeding. Arterial concentration of non-esterified fatty acids (NEFA) increased with underfeeding. The portal net release of all volatile fatty acids, 3-hydroxybutyrate and NH3 were linearly related to intake. The portal net flux of both essential and non-essential amino acids, and thus total amino acids, remained unchanged between levels H and M, and decreased between levels M and L. A significant net uptake for glycine and total non-essential amino acids occurred at level L. The portal net uptake of glucose, urea, glutamate and glutamine, and the portal net release of lactate and NEFA were not affected by underfeeding. Summation of portal energy fluxes indicated that 51 % of the metabolizable energy intake was recovered in the portal blood with the three levels of intake. In conclusion, no quantitative adaptation to spare energy, in terms of percentage of intake, occurred in PDV of short-term underfed ruminants, but the pattern of absorption of energetic nutrients was modified.

Four ewes, each fitted with a rumen cannula and with catheters in the mesenteric artery and portal and mesenteric veins, received continuous intrarumen infusions of water or of short-chain fatty acids (SCFA). SCFA infusions were isoenergetic (83 kJ/h) and provided rumen molar proportions (acetate : propionate : butyrate) of 70 : 20 : 10, 50 : 40 : 10 or 50 : 20 : 30. The rumen SCFA production rate with the basal diet was 90·0, 23·1 and 8·8 mmol/h for acetate, propionate and butyrate respectively. Portal net fluxes indicated that 74, 67 and 22–30 % of infused acetate, propionate and butyrate respectively, reached the portal vein. Portal net release of β-hydroxybutyrate increased with SCFA infusions, irrespective of the amount of butyrate infused. Portal net release of lactate decreased with high-butyrate infusion. Portal net uptake of glucose increased with the SCFA infusions. In ewes infused with water, a portal net uptake of total amino acids (AA) was observed. SCFA infusions decreased the uptake of nonessential AA (glutamate, glycine, but not glutamine) and increased the net release of tyrosine and essential AA (isoleucine, leucine). Portal net fluxes of AA were similar with both high-acetate and high-propionate infusions. Lower net uptake of glutamine and net release of most essential AA and some nonessential AA were observed with the high-butyrate infusion. Energetic summation of portal net release was not significantly different between the three SCFA infusions, although it tended to be lower with high-butyrate infusion. This may be related to the higher trophic effect of butyrate on the digestive mucosa.