The Digestion of Protein and

Ortiz, L.T., Centeno, C. and Trevino, J. (1993) Tannins in faba bean seeds effects on the digestion of protein and amino acids in growing chicks. Animal Feed Science and Technology 41, 271-278. 

The human intestine has evolved as a highly efficient organ to digest (i.e. hydrolyse) practically all the macromolecules in the human diet (albeit with the help of a few trillion bacteria ) with the exception of some plant fibres. To do this it possesses a formidable array of enzymes. This is particularly true for the digestion of proteins and peptides where peptidases are found in the stomach, are secreted by the pancreas in considerable quantities and are found on the surface of and inside intestinal epithelial cells. These enzymes work in a co-ordinated fashion to rapidly hydrolyse proteins. They present the major difficulty for designing oral delivery systems for therapeutic peptides, which may explain why 86 years after the first attempt to orally administer insulin (Bliss 1982), there is still not an oral insulin product available for diabetics. 

The Digestion of Protein and Nitrogenous Compounds in Ruminants Margaret I. Chalmers and R. L. M. Synge... 

The loss of nutritive value when protein or protein-rich foods are heated or stored in the presence of carbohydrates has been studied by a large number of groups (8,10,12,18,29,30). A decrease in the digestibility of proteins and in the availability of amino acids and carbohydrates after the Maillard reaction is shown in Table II. It can be concluded from this that the biologic value of proteins has also decreased. For example, in Table in one can see significant decreases in amino acids of egg albu-t... 

Digestibility of Proteins The consultation discussed in detail the various methods used for determining the digestibility of proteins and made the following recommendations ... 

Amide hydrolysis, a very important reaction in biochemistry, is a central reaction in the digestion of proteins and the breakdown of proteins within cells. However, most amide hydrolysis in the body is catalyzed by enzymes rather than by strong acids or bases. 

Dogs and cats are predominantly meat eaters and consume little fibrous material. Consequently their digestive tracts are adapted to the digestion of protein and fat and the large intestine is small. 

Fiber—Diets consisting of unrefined cereals and containing large amounts of fiber decrease the digestibility of proteins and increase the loss of protein in the feces. 

There are problems as well in the absorption of certain drugs in the presence of specific food components. L-Dopa absorption may be inhibited in the presence of certain amino acids formed from the digestion of proteins [43], The absorption of tetracycline is reduced by calcium salts present in dairy foods and by several other cations, including magnesium and aluminum [115-117], which are often present in antacid preparations. In addition, iron and zinc have been shown to reduce tetracycline absorption [118], Figure 17 illustrates several of these interactions. These cations react with tetracycline to form a water-in-soluble and nonabsorbable complex. Obviously, these offending materials should not be co-administered with tetracycline antibiotics. 

Most pancreatic secretion takes place during the intestinal phase. The intestinal hormone secretin stimulates release of a large volume of pancreatic juice with a high concentration of bicarbonate ion. Secretin is released in response to acidic chyme in the duodenum (maximal release at pH < 3.0). The intestinal hormone cholecystokinin is released in response to the presence of the products of protein and lipid digestion. Cholecystokinin then stimulates the release of digestive enzymes from the pancreas. 

The problem to be solved with respect to the chemical reactions that constitute metabolism and sustain life is that, without the action of catalysts, they are far too slow. Let s consider the digestion of the proteins themselves, an important constituent of our diet. In an enviromnent similar to that of our digestive system, several tens of thousand years would be required to digest half of the protein content of a typical meal in the absence of a catalyst. Clearly, this will not do. In reality, the stomach secretes one protein catalyst, the enzyme pepsin, and the pancreas secretes several enzymes that catalyze the digestion of proteins. In the presence of these enzymes, dietary proteins are fully digested and reduced to their basic constituents, the amino acids, in a matter of hours. Obviously, these enzymes are enormously potent catalysts." ... 

Asafetida, administered orally to albino rats at a dose of 250 mg% for 8 weeks, enhanced pancreatic lipase activity, stimulated pancreatic amylase and chymotrypsin. The stimulatory influence was not observed when their intake was restricted to a single oral dose " " ". Protein digestibility. Asafetida did not affect the digestibility of protein in sorghum " . ... 

Figure 8.15 Cartoon showing how proteins, polysaccharides and surfactants (emulsifiers) might be distributed at the triglyceride-water interface. Inter-facial complexation in vivo between adsorbed protein and charged polysaccharide in the gastrointestinal tract could affect digestion of protein and fat by forming structures that inhibit the accessibility and activity of enzymes (proteases and lipases). Reproduced from Dickinson (2008) with permission.

The digestion of proteins begins in the stomach, which secretes gastric juice—a unique solution containing hydrochloric acid and the proenzyme, pepsinogen ... 

Peptidases Involved in the Digestion of Blood and Tissue Proteins.353... 

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