Protein nutrition digestibility

Section VI consists of discussions of eleven special topics nutrition, digestion, and absorption vitamins and minerals intracellular traffic and sorting of proteins glycoproteins the extracellular matrix muscle and the cy-toskeleton plasma proteins and immunoglobulins hemostasis and thrombosis red and white blood cells the metabolism of xenobiotics and the Human Genome Project. 

Tannins derive their name from their ability to tan (i.e. they combine with protein). They render plants less palatable and impair digestion by binding with the buccal mucosa, dietaiy proteins, and digestive enzymes of the animal. Tannins are thought to bind to proteins upon destruction of plant tissue by herbivores. This reduces the nutritive value of the plant to the herbivore. Some tannins such as oak gallotannins, are even toxic to livestock and rabbits (Meyer and Karasov, 1991). However, Martin and Martin (1983) have questioned the role of tannins as plant defense against herbivores. 

Provides protein and digestible, high-calorie nutrition during an illness Kale... 

Studies performed over the years have contributed to better understanding of the interactions between proteins and tannins, which are important not only due to their astringency but also because of their impact on food nutritional characteristics, on human health, and on plant metabolism. It is clear that protein-tannin interactions are influenced by several factors, among which polysaccharides could be important because they are also present in tannin-rich vegetables. Much remains to be studied in this field, particularly the specific phenomenon that occurs between proteins, tannins, and polysaccharides that leads to a decrease in aggregation, and further studies are needed involving other salivary proteins and digestive enzymes. 

The digestion of heated or unheated soybean proteins by various enzymes is schematically compared with the nutritive values in Figure 18. Pattern A is typical of pepsin where, because of low pH of the reaction, the protein does not have to be denatured prior to addition to the reaction. Pattern B is typical of enzymes such as papain, bacterial neutral protease etc. where prior de-naturation of the substrate protein is required but there are no inhibitors of the enzyme present. Pattern C is typical of trypsin where prior heat treatment of the substrate protein is required to destroy inhibitors of trypsin as well as to denature the protein for digestion. The decrease in digestibility with prolonged heating in all three cases is due to modification of the substrate protein as described above. 

The synthesized or synthetic proteins previously discussed in terms of the genetic code are not necessarily the same as those that start out as nutritional or dietary proteins. However, digestive enzymes break down dietary proteins into the amino acid pool required for subsequent cell protein synthesis, as has been described. The proteins so synthesized variously become cellular structural components, enzymes and hormones, and blood plasma proteins. The latter are involved in cellular osmotic balances, that is, in ensuring a stable pressure difference across the cell walls. These blood proteins also transport substances through the vascular system, and assist in promoting inununity (Chaney, in Devlin, 1986, p. 1179ff). 

Papain Papaya Yeast and meat extracts beer chiU-proofing protein hydrolyzates meat tenderization leather bating, animal nutrition digestive-tiid anti-inllammatoiy... 

Many aspects of the usage of dietary protein were discussed in the chapter on nutrition. After the protein is digested by the proteolytic enzymes of the gastrointestinal tract, the free amino acids are transported inside the cells of the intestinal mucosa and from there released into the portal circulation. The portal blood carries the free amino acids in close contact with the hepatic cells. The amino acids are transported through the cell membrane inside the liver cell. 

Adapted from Sauer W C and de Lange K 1992 Novel methods for determining protein and amino acid digestibility values in feedstuffs. In Nissen S (ed.) Modern Methods in Protein Nutrition and Metaboiism, London, Academic Press. 

The introduction of amino acids directly into the blood stream, unlike the injection of whole protein as a plasma transfusion, presents no unusual physiological problem inasmuch as normal protein nutrition involves the entrance of these same builtfing stones of protein into the blood stream. There is, however, a difference between an injection into the systemic veins, whereby all the amino acids as such quickly reach all the tissue at one time, and the gradual, and perhaps inconstant absorption of variable amounts of various amino acids, after being subjected to bacterial action, into the portal vein and thence to the liver alone during the digestion of food protein. In order to evaluate the metabolism of intravenously injected amino acids, this difference must be scrutinized. 

Natural nutritional sweeteners are proteins, but their potency is so high that, if used, they would not be signihcant sources of energy. All protein sweeteners have a slow onset of sweet taste and the sweetness lingers for some time. They are hydrolysed in acidic media, which results in the loss of the sweet taste. It is expected that sweet proteins are digested just as any other dietary proteins. 

Following the formation of the deoxyketosyl derivative, the reactions leading to the formation of the brown pigments or melanoidins (Fig. 3) are not well defined. These reactions, however, are responsible for numerous flavours and odours, possibly for toxicity, and for a further reduction in protein nutritive value via destruction of amino acids and reduced digestibility. There are thought to be three main pathways in the advanced Maillard reaction. 

Animal Nutrition. Sulfur in the diets of mminant animals is beneficial to the animals growth (see Eeedsand FEED ADDITIVES). Sulfur increases feed intake, cellulose and dry matter digestion, and the synthesis of microbial protein. This results in increased meat, milk, and wool production (43). The special uses for sulfur in agriculture demonstrate a significant and continuing need for increased use of sulfur (44). 

Wool, as a keratin, is a highly cross-linked, insoluble proteinaceous fiber, and few animals have developed the specialized digestive systems that aUow them to derive nutrition from the potential protein resource. In nature, these few keratin-digesting animals, principally the larvae of clothes moths and carpet beetles, perform a useful function in scavenging the keratinous parts of dead animals and animal debris (fur, skin, beak, claw, feathers) that ate inaccessible to other animals. It is only when these keratin-digesting animals attack processed wool goods that they are classified as pests. Very often they enter domestic or industrial huildings from natural habitats such as birds nests. 

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