Comparative studies on the enzymatic absorption of protein hydrolysates in the small intestines of the rat. 3. The absorption of trypsin, thermitatic and trypsin thermitatic wheat gluten hydrolysates in comparison with equimolar mixtures of free amino acids

Tryptic, thermitatic, and tryptic-thermitatic wheat-gluten hydrolyzates as well as their equimolar amino-acid mixture were perfused through proximal and distal parts of the intestine (10 cm length) of non-narcotized rats. The total amino-acid concentration of the perfused solution was 50 mM. The tryptic hydrolyzate showed a significantly lower absorption of nitrogen and total amino acids than the amino-acid mixture. Both the supplied forms were very different as to their absorption pattern of the amino acids. The high variability of the percental absorption of the individual amino acids of the tryptic hydrolyzate results in a high coefficient of variation. The absorption of nitrogen and total amino acids from thermitatic and tryptic-thermitatic hydrolyzates is equal to that from the amino-acid mixture. In a peptidic form glutamic acid is more rapidly absorbed from the two hydrolyzates, and methionine from the tryptic-thermitatic hydrolyzate in both the intestinal parts. As to alanine and glycine this concerns only the distal intestinal part for both the hydrolyzates. There are no differences between the absorption patterns of the two hydrolyzates but in comparison with the amino-acid mixture and the tryptic hydrolyzate differences were evident. The coefficients of variation of both the hydrolyzates are significantly lower as compared to those of the tryptic hydrolyzate and the amino-acid mixture. All forms of supply are more rapidly absorbed in the distal than in the proximal part of the intestine.     

Comparative study of the absorption of enzymatic protein hydrolysates in the small intestine of the rat. 2. The absorption of tryptic, thermitatic and tryptic-thermitatic casein hydrolysates compared with the equimolar composition of free amino acids

Tryptic, thermitatic, and tryptic-thermitatic casein hydrolyzates as well as their equimolar amino-acid mixture were perfused through proximal and distal parts of the intestine (10 cm length) of nonanaesthesized rats. The total amino-acid concentration of the perfused solution was 50 mM. The absorption of nitrogen and total amino acids respectively did not reveal significant absorption advantages in favour of the hydrolyzates. In contrast to this, some peptidic bound amino acids of these hydrolyzates show a significantly better absorption as compared to free amino acids. At this, dependences of the kind of hydrolyzate and the part of the intestine are evident. Glutamic acid, e.g. is generally more rapidly absorbed when peptidic bound; methionine is more rapidly absorbed only from the thermitatic and tryptic-thermitatic hydrolyzates, and alanine and glycin only in the distal part of the intestine. Independent of the amino acid or peptide substrate the total absorption of all the amino acids is higher in the distal part of the intestine. The comparison concerning the ranking order of the single amino-acid absorption rates shows in the two parts of the intestine distinct differences between the amino-acid mixtures and the enzymatic hydrolyzates. The lowest differences were found between the thermitatic and the tryptic-thermitatic hydrolyzate. Both of them have approximately the same degrees of hydrolysis (30 and 35%, respectively). The variability of the amino-acid absorption from the three casein hydrolyzates is lower in comparison with the amino-acid mixture. The tryptic-thermitatic hydrolyzates have the lowest coefficients of variability.     

Zinc absorption from the small intestine in young calves.

Zinc-65 was injected directly into various sites throughout the small intestine of Holstein calves fed a low zinc diet. Zinc absorption was determined by comparing zinc-65 content of blood, liver, kidney, lung, heart, pancreas, rib, muscle, and other tissues. Tissue zinc-65 was plotted against site of injection expressed as percentage of intestinal length from proximal to distal ends. Zinc absorption occurred throughout the small intestine with the amount absorbed per centimeter of length about equal throughout the small intestine. This is in contrast to conclusions from studies of rats indicating more absorption in the proximal part of the small intestine. The difference appears to have been due to artifacts in the procedures with rats. However, species and dietary differences may have affected relative findings between this and earlier work.     

Ussing chamber results for amino acid absorption of protein hydrolysates in porcine jejunum must be corrected for endogenous protein

BACKGROUND: Ussing chambers have been used extensively as an ex vivo model to investigate intestinal nutrient absorption. In this study Ussing chambers were used to investigate the absorption of amino acids and peptides in pig jejunal tissue using a highly hydrolysed casein hydrolysate (PeptoPro®), casein and whey protein isolate after they had been digested with pepsin and pancreatin to simulate digestion products in the jejunum. Jejunal tissue was collected from three pigs and mounted into Ussing chambers, equilibrated, and the luminal chamber loaded with one of three test nitrogen sources. Luminal solution samples were taken every 10 min over a 90 min incubation period and the amino acid concentration determined. To determine the endogenous amino acid contribution of the tissue to the luminal solution, Ussing chambers containing no test N source (blanks) were prepared and treated similarly to the Ussing chambers containing the test N sources. RESULTS: The endogenous amino acid contribution was 0.5 mg in the luminal solution at time 0 and increased to 1 mg after 90 min. The mean amino acid absorption after 10 min incubation for the pre‐digested highly hydrolysed casein hydrolysate (16.6%) was significantly (P < 0.05) higher than for the pre‐digested casein (7.6%) and whey protein isolate (6.7%). CONCLUSION: Endogenous amino acids were a quantitatively significant portion of the luminal solution amino acids present in the Ussing chambers containing the test N sources. Ussing chambers may be a suitable tool for studying amino acid absorption of protein hydrolysates but correction for the endogenous amino acid contribution from the intestinal tissue must be made. Copyright © 2009 Society of Chemical Industry     

Digestion and absorption of protein along ovine gastrointestinal tract

Digestion and absorption of protein were determined in ovine gastrointestinal tract with cerium-141 as an unabsorbed reference substance. Nitrogen flows changed little in rumen and reticulum, but in the proximal small intestine flows increased because of secretion of .9 g nitrogen per day per kg body weight. This secretion included trypsin, chymotrypsin, elastase, and carboxypeptidases A and B; maximal activity was in proximal segments of the small intestine and decreased with distance from the pylorus. Activity of chymotrypsin decreased more rapidly than that of trypsin. Amino acid flows reflected the influx of protein in the duodenum; absorption was approximately 55% in the terminal ileum. No major changes of proportions of individual amino acids were observed. Overall nitrogen absorption was 72.6% of which 6% was in the large intestine. The major soluble protein fraction in the gastrointestinal tract consisted of peptides with molecular weight 7,000 to 14,000 daltons. Soluble high molecular weight protein was observed only in rumen and duodenum. Low molecular weight peptides and amino acids accumulated only in the proximal small intestine. Solubilization of protein and breakdown of peptides of 7,000 to 14,000 molecular weight appear to be rate limiting for protein absorption in sheep.     

Digestion and resorption of proteins]

A survey is given of the ultrastructure of the intestinal epithelial cell, especially of its lumenward membrane. Special attention is paid to the peptidases which are located in the ciliated border and within the cell. The authors deal with the purification of the membrane-bound aminopeptidase which is of importance in splitting dietary peptides and illustrate its specificity by the cleavage of casein. The amino acids which are liberated by peptide splitting have in part aminopeptidase-inhibiting properties. The possible digestion physiological consequences are discussed. In vitro experiments were performed to investigate the composition of the content of the distal part of the small intestine of the rat with regard to its possible dependence on the composition of various dietary proteins. The composition of the peptides of the intestinal content is essentially undependent of the amino-acid composition of the diet. There is no enrichment of certain amino acids. The importance of the resorption of the peptides is also evidenced by resorption studies in which enzymatic hydrolysates of proteins (i.e. peptide mixtures) were confronted with a free amino-acid mixture of the same over-all composition. Taking glycyl-glycine-glycine as a model, the authors demonstrate that, in determined ranges of concentration, tripeptides may in part be resorbed without degradation. Finally, the importance of peptide resorption is evaluated and conclusions are drawn as to further studies on the physiology and physiopathology of digestion.     

Effect of ruminal protein degradation of blood meal and feather meal on the intestinal amino acid supply to lactating cows

Four lactating cows fitted with ruminal cannulae and T-type cannulae in the proximal duodenum and terminal ileum were utilized to measure protein degradation in the rumen and amino acid flow to and absorption from the small intestine. Soybean meal, blood meal, feather meal, and a 50-50 combination of blood meal and feather meal provided 50% of the protein in diets that contained 50% grain mix, 40% corn silage, and 10% alfalfa pellets on a DM basis. Ruminal degradation of dietary CP was 53, 43, 32, and 37% for diets containing soybean meal, blood meal, feather meal, and the combination of meals. Cows fed the latter two diets also had lower ruminal NH3 concentrations and efficiency of bacterial protein synthesis compared to those fed the soybean meal diet. Total tract N digestibility was lower for diets containing feather meal (63.4%) and a combination of meals (66.3%) than the soybean meal diet (78.5%). Total amino acid flow to the duodenum was 19.3 and 15.6% higher for cows fed the feather meal and combined meal diets, respectively, compared with the soybean meal diet. Total amino acid absorption from the small intestine was higher as well as absorption of individual amino acids for the combined meal diet compared with the soybean meal diet. Absorption of individual amino acids, expressed as a percentage entering the duodenum, was lowest for the feather meal diet. Results from this study show that feeding a combination of blood meal and feather meal instead of soybean meal can increase intestinal supply and absorption of amino acids in dairy cattle.     

Protein degradation in rumen and amino acid absorption in small intestine of lactating dairy cattle fed heat-treated whole soybeans

Four lactating Holstein cows fitted with rumen cannulae and T-type cannulae in proximal duodenum and terminal ileum were used to measure protein degradation in the rumen and amino acid flow and absorption in the small intestine. Soybean meal, whole soybeans, and whole soybeans extruded at 132 and 149 degrees C provided 50% of the protein in diets that contained 51% grain, 36% corn silage, and 13% alfalfa hay (dry matter). Spot samples of digesta were collected from duodenum and ileum during 96 h, and lanthanum was an indigestible marker to estimate flow and digestibility of nutrients. With diaminopimelic acid as a microbial marker, apparent degradations of dietary crude protein in the rumen were 73, 80, 66, and 60% for diets containing soybean meal, whole soybeans, and whole soybeans extruded at 132 and 149 degrees C. Because of the extensive degradation of protein with the raw soybean diet, less total amino acids reached the duodenum, and because of decrease of availability, absorption from the small intestine (g/day) was lowest with this diet. Feeding diets containing extruded whole soybeans increased availability of total essential amino acids in the small intestine compared with diets containing soybean meal and whole soybeans. Absorption from the small intestine (g/day and percent entering) of individual amino acids was generally higher for extruded whole soybean diets.     

The effect of amino acid and peptide alimentation on the determination of endogenous amino acid flow at the terminal ileum of the rat

Endogenous ileal amino acid (free + bound) flow was determined in four 190-g male rats given a diet whose sole nitrogen source was enzyme hydrolysed casein and compared with that of six rats whose diet contained synthetic amino acids as the only nitrogen source but excluding alanine, glutamic acid and serine, and six rats fed a protein-free diet. The enzyme hydrolysed casein, a mixture of free amino acids and oligopeptides, was assumed to be completely absorbed in the small intestine of the rat. A further seven rats were given an enzyme hydrolysed casein-based diet and their ileal digesta were treated, post-collection, with perchloric acid to precipitate soluble proteins. The latter procedure removed the need to assume complete absorption of the casein nitrogen. The endogenous flow of amino acids for enzyme hydrolysed casein-fed rats was higher than that for the protein-free diet (P < 0.05) which did not differ from the synthetic amino acid diet for the flows of alanine, glutamic acid and serine. The high apparent digestibility of the synthetic amino acids not excluded from the diet indicated that their ileal excretions were mainly of endogenous origin. It would appear, therefore, that the protein deplete state per se does not influence endogenous amino acid flow at the terminal ileum of the growing rat, but there is a direct effect of small peptides on the net loss of endogenous amino acids from the small intestine. The estimates of endogenous amino acid flow obtained following the perchloric acid treatment of digesta were unrealistically low and thus inconclusive, but raised doubt as to the eficiency of perchloric acid in precipitating protein from rat ileal digesta.     

Nucleosides are efficiently absorbed by Na(+)-dependent transport across the intestinal brush border membrane in veal calves

In previous work, a comparatively high capacity for Na(+)-dependent transport of nucleosides across the intestinal brush border membrane (BBM) was observed in dairy cows, which might be related to digestion of the large amount of nucleic acids present in ruminal microorganisms in the ruminant small intestine. If this were the case, the capacity for Na(+)-dependent intestinal nucleoside transport should be much lower in veal calves, in which only small amounts of nucleic acids, nucleotides, and nucleosides reach the small intestine via the milk replacer. To test this hypothesis, we investigated Na(+)-dependent transport of 3H-labeled thymidine and guanosine across the BBM using BBM vesicles (BBMV) isolated from the small intestine of veal calves. In the presence of a transmembrane Na+ gradient both substrates were transported against a concentration gradient. Inhibitory studies showed that thymidine and guanosine are transported by two different transporters with overlapping substrate specificity, one accepting predominantly pyrimidine nucleosides (N2) and one accepting particularly purine nucleosides (N1). Nucleoside transport was inhibited by glucose along the whole small intestine. Maximal transport rates similar to those in dairy cows were obtained for the proximal, mid-, and distal small intestine. These findings suggest that the high absorptive capacity for nucleosides is a genetically fixed property in the bovine small intestine, which is already present in the preruminant state of veal calves. It may contribute to the high digestibility of nucleic acids observed by others in veal calves receiving milk replacer supplemented with RNA. Its main function may be the efficient absorption of nucleosides resulting from the digestion of nucleic acids associated with desquamated enterocytes. Due to the limited de novo synthesis of nucleotides in enterocytes intracellular uptake of nucleosides across the BBM may contribute to nucleic acid synthesis in enterocytes and thus may have a trophic effect on the intestinal epithelium.     

The intestinal phase of peptide absorption

Peptides and not amino acids are the prevailing degradation products of protein digestion which are formed in the intestinal lumen and are absorbed from the mucosa. These two families differ in absorption. The differences become manifest when the absorption of peptide mixtures is compared with that of equimolecular mixtures of free amino acids. The absorption of peptides occurs in two different ways: 1. Transport of intact peptides through the membrane into the mucosal cell and subsequent hydrolysis by intracellular peptide hydrolases. 2. Hydrolysis of the peptides by peptide hydrolases localized on the luminal side of the mucosal cell membrane and subsequent transport of the amino acids thus formed through the membrane. The two mechanisms of absorption do not exclude each other. The way by which energy is supplied for the transport is not yet elucidated. The transport of intact peptides is of nutritive importance only in case of dipeptides and tripeptides. It enables in particular the introduction of peptides that cannot be cleft by membrane-bound peptide hydrolases. The hydrolysis of peptides by membrane-bound peptide hydrolases and the subsequent transport of released amino acids is of importance for long-chain peptides. The difference in absorbing behaviour between the free amino acids released in the intestinal lumen and the amino acids released by peptide hydrolases at the mucosal membrane is discussed.     

Features of the absorption of modified fish proteins

The characteristics of absorption of modified fish protein were studied in comparison with those non-modified. It has been established that protein acetylation process reduces the absorption intensity of lysine, sulfur-containing amino acids as well as amino acids with a ramified chain. At the same time the final stages of protein assimilation on the surface of the small intestine mucosa are attended by appearance of amino acids at the free state, except lysine which in the form of acetyllysine enters blood flow. Thus, further investigation of the character of acetylated protein metabolism in the body is necessary, as their practical use in food industry is promising.     

Amino acid composition of non-absorbed peptide fractions in rat small intestines. III. Feeding of wheat gluten and molasses yeast. Essential amino acid content of feces]

The authors investigated the nitrogen content of different fractions and in particular the aminoacid composition of the trichloroacetic acid (TCA)-precipitable and TCA-soluble peptides in the distal small intestine of rats which had been fed experimental diets (nitrogen-free or containing casein, wheat gluten or molasses yeast as a protein carrier). Parallel with this, they determined in growing rats the nitrogen and amino-acid digestibility of molasses yeast and wheat gluten according to the technique of faecal analysis, and studied the amino-acid composition of the faecal protein. Independently of the dietary protein fed, the peptide fractions of the content of the intestine showed an amino-acid composition that was largely similar to that found in case of nitrogen-free diet. The amino-acid composition of the faecal protein is, independently of the dietary protein given, relatively constant and corresponds approximately to the intestinal loss protein. There is agreement between the amino-acid composition of the TCA-precipitable peptide fractions and those of the corresponding faecal proteins. These components seem to be of endogenous origin.     

Protein assimilation and acid proteinases in the postnatal gastrointestinal tract in experimental studies

Proximal-distant gradient of the lysosomal proteinase activity distribution is observed in the mammals at the postnatal period of development. In various species of mammals the proximal-distal gradient of the lysosomal proteinase distribution is attended by the shift of the final stages of the intestinal digestion to the distal part of the small intestine. These features are typical of the protein digestion in the mammals at the postnatal period of development. The protein digestion in adult mammals is characterized by a uniform distribution of lysosomal proteinases between the small intestine parts and by the completion of the protein intestinal digestion in the proximal part of the small intestine.     

Segmental distribution and expression of two heterodimeric amino acid transporter mRNAs in the intestine of pigs during different ages

BACKGROUND: Segmental distribution and expression of two heterodimeric amino acid transporter mRNAs during different ages were evaluated in pigs along the horizontal axis of the intestine. RESULTS: The intestinal distribution of b^{0, +} AT and y⁺LAT1 mRNA at day 90 showed that for b^{0, +} AT the mRNA levels were increased from the proximal to distal part of the small intestine (P < 0.05) and dropped dramatically in colon (P < 0.05). The ileum had the highest b^{0, +} AT mRNA abundance and the ileum had the lowest. Compared to b^{0, +} AT, the y⁺ LAT1 mRNA levels were decreased from the proximal to distal part of the small intestine (P < 0.05). The duodenum has the highest y⁺ LAT1 mRNA abundance. The mRNA abundance of b^{0, +} AT mRNA increased linearly (P < 0.0001) from day 1 to day 150 in ileum. CONCLUSION: The mRNA expression of heterodimeric amino acid transporters (b^{0, +} AT and y⁺LAT1) was not only differentially regulated by age but also differentially distributed along the intestine of piglets at early stages and growing stages of life, which may be related to luminal substrate concentration as well as amino acid requirement and hormones. Copyright © 2008 Society of Chemical Industry     

Characteristics of collagen's material bifidogenic properties

It is still essential to search for new, available food ingredients with bifidogenic effect, to study their safety, efficacy and production effectiveness upon the creation of functional foods. The review considers protein products such as collagens and their hydrolyzates, which are used in culture mediums as growth factor. They are treated, besides carbohydrate prebiotics, as potential bifidogenic nutrients. Collagen hydralyzates contain all amino acids, required for bifidobacteria growth. That is why it is considered essential to provide control over its biosafety. However, recyclable materials of animal origin are included into a list of Specific Risk Materials of prion disease agents transmitting. Collagen hydralyzates are preserved up to distal intestine parts. This fact approximates their qualities to oligosaccharids' type of prebiotic food fibers, related to the lack of absorption and hydrolytic stability. The additional study of mechanisms of bifidobacteria's forcing is required. It can be made at the expense of the modification of the albuminous cell metabolism during the collagen hydralyzats' unilization.     

Digestion and absorption of lipids and bile acids in sheep fed stearic acid, oleic acid, or tristearin

Sheep were fed diets containing 7.5% added stearic acid, oleic acid, or tristearin for 21 days. In addition, 50 microCi/kg cerium-141 was included for the last 10 days on experimental diets as an unabsorbed reference substance. In the rumen dietary triglycerides were approximately 50% hydrolyzed, and hydrogenation resulted in saturation of the free fatty acid fraction. Some net synthesis of phospholipids, presumably microbial phospholipids, occurred in the rumen. In the intestine immediately distal to the pylorus, extensive secretion of bile acids, cholesterol, phospholipids, triglycerides, free fatty acids, and lipase occurred. This resulted in doubling of fatty acid fluxes through the duodenum. These endogenous secretions were reabsorbed rapidly however, with the major site of lipid and bile acid absorption in the region .6 to 4 m distal to the pylorus. Additional but less absorption occurred in the more distal segments of the small intestine. Overall absorption of stearic acid, oleic acid, and tristearin supplements was in the range 60 to 70%, and no differences were apparent between fats. Unsaturated fatty acids were over 90% absorbed as compared with 55 to 65% for saturated fatty acids. No significant effect of any of the supplements was observed on ruminal total volatile fatty acids, ratios of volatile fatty acids, or on overall cellulose or caloric digestion.     

活性炭静态吸附草鱼蛋白水解物中氨基酸特性的研究

研究了6种活性炭对草鱼蛋白水解物中氨基酸的吸附情况。发现AK-220型活性炭的静态吸附量最大,且吸附可使酶解液颜色和风味有良好改善;AK-220对芳香氨基酸（AAA）的吸附能力明显优于其对支链氨基酸（BCAA）的吸附程度,同时还可吸附一定数量的肽分子。     

Amino Acid Absorption in Portal Blood After Duodenal Infusions of a Soy Protein Hydrolysate Prepared by a Novel Soybean Protease D3

ABSTRACT:  The intestinal absorption of amino acids from decapeptide was investigated in rats under unrestrained conditions. The soy protein hydrolysate utilized in the experiment was produced by a novel soybean protease D3. The enzymatic features of protease D3 showed high homology with cathepsin L and cathepsin K and the average molecular weight of D3 hydrolysate is approximately 1200. We compared the intestinal absorption of D3 hydrolysate in portal blood with that of an amino acids mixture and soy protein with the same amino acid composition by determining the concentration of individual amino acids after a single administration of a nitrogen source. The absorptive velocity and intensity of each amino acid were calculated from its rate of elevation in the portal blood. And in most cases, these were higher in the D3 hydrolysate than in amino acids mixture and protein. The proportion of the amount of each amino acid absorbed in portal blood from D3 hydrolysate was much more like the composition of the administrated amino acids than like that from the amino acids mixture. The result of in vitro digestion assay indicated that D3 hydrolysate was hydrolyzed easier than the hydrolysates produced by microbial proteases. This is the first report to demonstrate that the D3 hydrolysate, which contains decapeptide as a dominant fraction, was more rapidly utilized than the amino acids mixture and protein as is the case with di-, tripeptides. This suggested that this hydrolysate could be available for nutraceutical use as well as use in nutritious foods for athletes and patients.     

Egg yolk protein and egg yolk phosvitin inhibit calcium, magnesium, and iron absorptions in rats

ABSTRACT:  Egg yolk decreases the absorption of iron. The effects of egg yolk protein and egg yolk phosvitin on the absorption of calcium, magnesium, and iron were investigated by in vivo studies. Male Wistar rats were fed purified diets containing casein, soy protein, or egg yolk protein for 14 d. The apparent absorptions of calcium, magnesium, and iron in the rats fed the yolk protein-based diet were lower than those in rats fed the casein- and soy protein-based diets. The apparent phosphorus absorption and the apparent protein digestibility in the yolk protein group were lower than those in the casein and soy protein groups. In the feces of the yolk protein group, serine comprised more than 30% of the amino acids. The addition of egg yolk phosvitin to the casein diets at levels of 1% and 2% (w/w) produced effects on calcium and magnesium absorptions similar to those produced by the diet containing yolk protein. The tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern suggested that phosphopeptide fragments having molecular masses of 28, 22, and 15 kDa were evident in the contents of the small intestine of the rats fed phosvitin diets. These results indicate that yolk protein, when compared with casein and soy protein, decreases calcium and magnesium absorption via the resistance of phosvitin to proteolytic action.