Nutritional value and intestinal effects of dipeptides and tripeptides. Comparison with their issuing bovine plasma protein in rats

Supramolecular hydrogels from unprotected dipeptides: a comparative study on stereoisomers and structural isomers

Amino acid stereoconfiguration has been shown to play a key role in the self-assembly of unprotected tripeptides into hydrogels under physiological conditions. Dramatic changes were noted for hydrophobic sequences based on the diphenylalanine motif from the formation of amorphous aggregates in the case of homochiral peptides to nanostructured and stable hydrogels in the case of heterochiral stereoisomers. Herein, we report that by further shortening the sequence to a dipeptide, the overall differences between isomers are less marked, with both homo- and hetero-chiral dipeptides forming gels, although with different stability over time. The soft materials are studied by a number of spectroscopic and microcopic techniques, and single-crystal X-ray diffraction to unveil the supramolecular interactions of these hydrogel building blocks.

Partial substitution of di- and tripeptides for native proteins in sea bass diet improves Dicentrarchus labrax larval development

To determine whether incorporation of peptides into diets can improve larval development, sea bass (Dicentrarchus labrax) larvae were fed for 21 d one of three isonitrogenous, isoenergetic semipurified diets in which enzymatic hydrolysate (75% di- and tripeptides) of fish meal proteins was substituted for 0, 20 or 40% of native fish meal proteins. Growth and survival were significantly greater (P < 0.05) in larvae fed peptide diets compared to those fed only native protein, with the best performance exhibited by those fed the 20% level of peptides. Chymotrypsin activity was much higher in groups fed peptide diets compared to that fed all native protein (P < 0.001), indicating a greater proteolytic capacity of the pancreas. At the intestinal level, activities of the brush border enzymes, aminopeptidase, maltase and gamma-glutamyl transpeptidase, increased with age while the cytosolic enzyme, leu-ala peptidase, decreased with age (P < 0.001). These changes in enzymatic activities correspond to the normal development of intestinal digestion. This development occurred earlier in the group fed 20% peptide-substituted diet than in the two other groups. The better larval performances observed in groups fed diets containing peptides can be related to the enhanced proteolytic capacity of the pancreas and the earlier development of intestinal digestion.

Antigenicity and nutritional value of selected milk proteins and their hydrolysate in growing rats

Two liquid diets containing selected milk proteins (SMP) or its small peptide hydrolysate (SPH) were fed to growing rats for 2 wk and the effects on growth, nitrogen balance, and small intestine adaptation were determined. Residual antigenicity of the SPH diet as measured by immunodot was reduced by 98.8%. Nitrogen intakes were not different. Weight gain was significantly higher in rats fed the SMP diet. In contrast, the absolute nitrogen balance was similar, suggesting that protein storage was identical with the two diets. A better nitrogen digestion-absorption rate with the SPH diet was observed as evidenced by the significantly increased fecal excretion with the SMP diet. Small intestine adaptation showed no difference between the two diets for mucosal weight, protein content/10 cm as well as for sucrase, glucoamylase, and N-aminopeptidase total activity/10 cm or specific activity (mU/mg protein). The DNA content of the mucosa/10 cm was significantly higher suggesting a mucosal hyperplasia in the SPH diet. The data suggest that in rats the SPH diet leads to nitrogen retention and small intestine adaptation similar to that of the SMP diet, despite better body weight gain by the latter.

Effects of native and hydrolyzed whey protein on intestinal repair of severely starved rats at weaning

The aim of this study was to evaluate the effect of two sources of dietary nitrogen (isolated whey protein and hydrolyzed whey protein) on the intestinal repair of malnourished rats at weaning. The malnutrition was achieved by a 3 days' starvation period. Normally fed male Wistar rats were used as controls. Intestinal repair was studied after a refeeding period of 4 days. The parameters studied included nitrogen balance, lactase, sucrase, isomaltase, and maltase activities of the jejunum; liver acetylcholinesterase and glutamate dehydrogenase activities; and the serum amino acid profile. In addition, tests of intestinal permeability to macromolecules were performed by measurement of ovalbumin and beta-lactoglobulin in serum. Both diets of led to the recovery of the severely starved rats, in terms of the values of all the parameters evaluated. The serum beta-lactoglobulin was the only exception, because its concentration was significantly lower in the normally fed animals. This study suggests that the intestinal mucosal barrier is not completely repaired, even after a 4-day refeeding period, to the point of being suitable to accept an increase in the uptake of antigens.

Influence of casein and casein hydrolysate diets on nutritional recovery of starved rats

BACKGROUND

The aim of this study was to compare the effects of two diets, which differed in their protein source (casein and casein hydrolysate), on the nutritional recovery and intestinal repair of undernourished rats at weaning after a 3-day fasting period. Profound alterations in gut structure and signs of malnutrition appeared after the starvation period.

METHODS

The casein hydrolysate was prepared by enzymatic hydrolysis and ultrafiltration. Rats were refed the casein-based or the casein hydrolysate-based diet for 96 hours. Normal-fed male Wistar rats at weaning were given the casein diet for 7 days and were used as controls. Liver acetylcholinesterase, glutamate dehydrogenase activities, serum amino acid profiles, jejunal oligosaccharidases, alkaline phosphatase, and leucine aminopeptidase activities were studied. Intestinal permeability to intact proteins was also tested by using ovalbumin and measuring its concentration in serum.

RESULTS

Intestinal and liver enzyme activities and serum amino acid profiles reached normal values after 96 hours of refeeding, regardless of the diet used. Glutamate dehydrogenase activity remained higher in both diet groups. Intestinal permeability to ovalbumin remained significantly increased only in the group refed the casein diet.

CONCLUSIONS

Our results show that 4 days of refeeding are sufficient for complete intestinal recovery after fasting, provided the dietary protein source is a casein hydrolysate. We suggest that patients with malnutrition or malabsorption syndrome should be fed formula composed of enzymatic protein hydrolysates (because of their low antigenicity) rather than enteral formulas composed of intact proteins.

Protein v. enzymic protein hydrolysates. Nitrogen utilization in starved rats

The present study was carried out to compare the effects of four isoenergetic and isonitrogenous diets on the N utilization, total serum protein concentration and serum amino acid profile in starved rats at weaning. These diets differed only in the molecular form of two milk proteins (whey protein and casein), which were either native or partly hydrolysed. Male Wistar rats at weaning were fasted for 3 d and then refed with one of the four diets for 48 h. No differences were observed in the body weight gain, protein digestibility and total serum protein concentration between groups after the refeeding period and all the N balances were positive. N retention was higher in the two groups of rats given the protein-hydrolysate-based diets compared with those given the intact-protein-based diets. This was associated with a lower urinary N excretion in rats, given the whey-protein-hydrolysate and the casein-hydrolysate diets. Despite this fact, the serum amino acid pattern of rats given the hydrolysed protein diet was very similar to that of those given the corresponding native protein diet. In conclusion, we have proved that enzymic hydrolysates from milk proteins have equivalent effects to native proteins in recovery after starvation in rats at weaning, on N absorption, total serum protein concentration and serum amino acid profile, and even give a higher N retention. We did not observe any harmful effect in using protein hydrolysates instead of native proteins.