Amino acids nutritional consequences

Nutritional Effects Due to the Blockage of Lysine. The most important Maillard reaction in food proteins occurs with the c-amino group of lysine. Since lysine is an essential amino acid, nutritional consequences can be expected. These depend on the chemical structure of the lysine derivatives formed. 

The nutritional consequences of an excess protein diet are the same as those of an excess carbohydrate or excess fat diet lipid biosynthesis and fat deposition. Additionally, the protein amino groups must be detoxified and eliminated. The nutritional consequences of a diet lacking complete protein—that is, one that doesn t supply the essential amino acids in the proportions needed for synthesis of proteins and neurotransmitters—also include excess ammonia generation. In this case, muscle proteins are degraded to supply enough of the limiting essential amino acid. The other amino acids are broken down, with the carbon chains metabolized into carbohydrates (and, potentially lipid). The leftover amino groups must then be eliminated as urea. 

In this paper we describe seme of the factors which influence racemization of amino acid residues in food proteins and discuss toxicological and nutritional consequences of feeding alkali-treated food proteins. 

Nutritional Implications. The nutritive quality of any protein depends on three factors amino acid composition, digestibility, and utilization of the released amino acids. Bacemization brought about by processing can impair the nutritive value of proteins by (a) generating non-metabolizable forms of amino acids (D-enanticmers), (b) creating peptide bonds inaccessible to proteolytic enzymes, and (c) toxic action (or interaction) of specific D-enanticmers. Little is known concerning the health consequences of human consumption of racemized proteins. No study has specifically evaluated amino acid losses due to racemization within food proteins. 

Friedman, M. (1977). Crosslinking amino acids—stereochemistry and nomenclature. Li "Protein Crosslinking Nutritional and Medical Consequences", (M. Friedman, ed.), Plenum Press, New York, pp. 1-27. 

Animal experiments have shown that faulty nutrition, i.e. > 90% fat, < 10% protein and < 2 mg choline per day, leads to pronounced fatty fiver and even fatty cirrhosis within a few weeks. The same changes could be observed when the protein intake remained more or less normal, while extremely little methionine and choline was offered. With a partial surplus of certain foodstuffs, the special nature of the excessive nutritional components is also of considerable importance. The term partial malnutrition may, for example, be associated with a pronounced protein deficiency (and thus possibly inadequate production of lipoproteins) or a lack of lipotropic substances (such as methionine, choline, cystine, glycocoUbetaine, pyridoxine, casein and various N- or S-methylated substances). Protein deficiency has particularly severe consequences when toxic substances are absorbed at the same time or when the organism has to fight bacterial or parasitic infections. A diseased liver reacts to both a serious deficiency in and an excessive supply of different nutrients (e.g. proteins, certain kinds of amino acids, various lipids, trace elements) with unfavourable or even complicative developments during the course of disease. 

Precipitates can develop in parenteral nutrition admixtures because of a number of factors such as the concentration, pH, and phosphate content of the amino acid solutions, the calcium and phosphorus additives, the order of mixing, or the mixing process. The consequences can be serious. In one cohort study of hospitalized patients who received peripheral parenteral nutrition, a subgroup developed unexplained chest pain, dyspnea, cardiopulmonary arrest, or new interstitial infiltrates on chest radiograph. A change in the amino acid source of a parenteral nutrition mixture was associated with respiratory adverse events that ranged from interstitial infiltrates to sudden death. The events apparently resulted from infusion of calcium phosphate precipitate in an opaque admixture, and the deposition of the crystals in the pulmonary microvasculature (147). 

Folic acid or the folate coenzyme [6] is a nutritional factor both for the parasites and the hosts. It exists in two forms, viz. dihydro- and tetrahydrofolic acids [4,5] which act as cofactors involved in the transfer of one carbon units like methyl, hydroxymethyl and formyl. The transfer of a one carbon unit is associated with de novo synthesis of purines, pyrimidines and amino acids. Mammals can not synthesize folate and, therefore, depend on preformed dietary folates, which are converted into dihydrofolate by folate reductase. Contrary to this, a number of protozoal parasites like plasmodia, trypanosomes and leishmania can not utilize exogenous folate. Consequently, they carry out a de novo biosynthesis of their necessary folate coenzymes [12]. The synthesis of various folates follows a sequence of reactions starting from 2-amino-4-hydroxy-6-hydroxymethyldihydropteridine (1), which is described in Chart 4 [13,14]. 

The occurrence of heat- and chemical-induced transformations of tryptophan and the nutritional and toxicologic consequences suggest a need for additional research to define possible approaches to prevent or minimize the formation of antinutritional and toxic tryptophan condensation and oxidation products in foods. The possible beneficial effects of antioxidants such as vitamins C and E, carotenes, flavonoids, indole derivatives, selenium compounds, and sulfur amino acids in enhancing the stability of tryptophan in foods need to be investigated. 

The following Biochemical Connections box describes an important practical aspect of the amino acid composition of proteins. This property can differ markedly, depending on the source of the protein (plant or animal), with important consequences for human nutrition. 

D-Amino Acids in Processed Proteins Their Nutritional Consequences... 

V. C. Sgarbieri, J. Amaya, M. Tanaka, and C. O. Chichester, Nutritional consequences of the Maillard reaction. Amino acid availability from fructose-leucine and fiirctose-tryptophan in the rat, J. Nutr., 103 (1973) 657-663. 

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