Nutrition, importance

Amino acids are the main components of proteins. Approximately twenty amino acids are common constituents of proteins (1) and are called protein amino acids, or primary protein amino acids because they are found in proteins as they emerge from the ribosome in the translation process of protein synthesis (2), or natural amino acids. In 1820 the simplest amino acid, glycine, was isolated from gelatin (3) the most recendy isolated, of nutritional importance, is L-threonine which was found (4) in 1935 to be a growth factor of rats. The history of the discoveries of the amino acids has been reviewed... 

Choline was isolated from ox bile in 1849 by Strecker. During 1900 to 1920, observations led to interest in the vasodepressor properties of the esters of choline, and in the 1920s it was shown that acetylcholine was presumably the "vagus-substance." The nutritional importance of choline was recognized in the 1930s, when it was found that choline would prevent fatty infiltration of the Hver in rats. Subsequent observations showed that choline deficiency could produce cirrhosis (1) or hemorrhagic kidneys (2) in experimental animals under various conditions. 

Dietary /1-carotene, a nutritionally important source of vitamin A, exhibits a protective effect against cancer risk31,32. The deuteriated compound, 10,10, 19,19,19,19, 19, 19 -2H8-/S-carotene, 32, has been obtained33 by double condensation of the C-15 Wittig salt 33 with the symmetrical C10 dial 2,7-dimethyl-2,4,6-octatrienedial, 34 (equation 13) for the study of /J-carotene metabolism in humans. 

Both lipases and lipoxygenases are present in the bran and the germ. Phytases are nutritionally important as they liberate the phosphorus, of which approximately 70% is in the kernel bound to phytin. Phytin blocks the intestinal absorption of both iron and calcium. Phytase is also present in yeast, which is why leavened bread is nutritionally superior to unleavened bread. There have been concerns about the incidence of rickets among those of South Asian origin who eat chapattis, live in the UK, and have a tendency to keep their skin covered up from the sun. 

Phytic acid (Figure 1) constitutes 1 to 5% by weight of most nutritionally important plant seeds (Table I) and... 

Despite the wealth of information available on the biochemistry, genetics, and nutritional values of plant proteins, people eat foods that look, smell, and taste good not because of nutritional importance. Thus, new blended plant foods or protein-supplemented snacks or food products will have to look and taste like the traditional items if they are to gain sufficient acceptance to become commercially feasible. Absolute food... 

In the preceding chapter we have assembled evidences that each individual s nutritional needs are also distinctive from the quantitative standpoint. Although every nutritionally important mineral, amino acid, and vitamin is needed by every individual, it followsif biochemical individuality existsthat the needs are quantitatively distinctive for each individual. Evidence has been presented in the preceding chapter that this is actually the case and that the divergences for many items are wide. 

Finally, they may be classified on the basis of whether they are nonessential, essential (exogenous), and conditionally essential amino acids. Food and tissue proteins contain 20 amino acids of nutritional importance. Nine of these amino acids (histidine (His), He, Leu, Lys, methionine (Met), Phe, Thr, Trp, and Val) cannot be synthesized by the body and they are therefore essential or indispensable nutrients that must be... 

While some metals are nutritionally important, there is another group with no beneficial biological effects and in some cases serious toxic effects. Our complex relationship with metals is well illustrated by lead, which we have used for a variety of purposes since ancient times. In the last hundred years, lead was extensively used in paint and as a gasoline fuel additive. In the last 30 years, it was recognized... 

The absorption of vitamins K2, which are found mainly in cheese, curd cheese, and natto, is much higher and may be almost complete. Thus the nutritional importance of menaquinones is often underestimated. The vitamin K activity is related to the activation of specific proteins involved in blood clotting and bone metabolism. Clinical vitamin deficiency due to dietary inadequacy is rare or nonexistent in healthy adults, thanks to the widespread distribution of the vitamin K in foodstuffs and the microbiological flora of the gut, which synthesizes menaquinones. Only infants up to 6 months are at risk of bleeding due to a vitamin K deficiency. No data on negative effects of an overdose of vitamin K are found [417]. 

Englyst,H. N., Kingman, S. M., Cummings, J. H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition, 46, S33-S50. 

Excessive heat can cause destruction of amino acid residues. The amino acid most susceptible to direct heat destruction is cystine. Although not an essential amino acid, cystine does have a sparing effect on the dietary requirement for methionine. As a result, cystine destruction can be nutritionally important. In addition, many vegetable proteins are limiting in the sulfur amino acids. Cystine destruction would be particularly harmful for these proteins. 

No adverse effects of either UHT processing or storage on the nutritional properties of milk fat have been demonstrated. Although increases in the milk s free fatty acid content have been noted when UHT milk is stored at room temperature rather than refrigerated, these changes do not appear to affect the nutritional value of the milk. No changes of nutritional importance have been noted in the carbohydrate components of UHT milk (Ford and Thompson 1981). 

Members of the raffinose family of oligosaccharides are present in appreciable concentrations in the nutritionally important food-legumes these are known to cause flatulence in man and other animals. Blair and coworkers144" quantitated the production of flatus in man,... 

Coloring fresh food is not permitted as a matter of principle. As a rule, coloring is used only for processed food with no color of its own or in which only residual amounts of color remain. Food must not be colored to simulate a higher level of nutritionally important components or, worse, to mask poor quality or spoilage. 

Phenolics not only exert negative growth effects by noncovalent interactions, but also by covalent interactions. Oxidative enzymes such as polyphenol oxidases (PPO) and peroxidases (POD) oxidize phenolics, monophenols, and diphenols into reactive molecular species such as quinones and quinone methides, which covalently bind to nucleophilic residues in dietary proteins such as -SH, -NH2 residues of nutritionally important amino acids such as cysteine and lysine, thereby decreasing the nutritive values of dietary proteins (Figure 7) 55... 

Manganese is a nutritionally important trace element for chicks. Dietary energy and protein sources contain very little bioavailable Mn, and these feed ingredients reduce the biopotency of inorganic Mn supplements. This adverse effect is exerted primarily in the intestine as a result of reduced Mn absorption and is mediated by the fiber and/or ash components of the feedstuffs. Gut absorption efficiencies are higher when a phytate-and fiber-free casein-dextrose diet is fed than when a corn-soybean meal diet is fed. Dietary interrelationships exist between Mn and Co and between Mn and Fe. Cobalt increases Mn absorption and may precipitate Mn toxicosis. Excess dietary Mn reduces Fe utilization, but excess Fe does not affect Mn utilization. Eimeria acervulina infection increases Mn absorption. 

Liu, J.C., Ockenden, I., Truax, M., and Lott, J.N.A., 2004, Phytic acid-phosphorus and other nutritionally important mineral nutrient elements in grains of wild-type and low phytic acid (Ipal-X) rice. Seed Sci. Res. 14 109-116. 

In addition to its provitamin A role, p - carotene is a radical trapping antioxidant and may be nutritionally important in its own right both as an antioxidant and possibly also through direct actions that are independent of retinoids. Other carotenoids that occur in foods, and circulate in the bloodstream, also have free radical trapping activity, and, hence, potential metabolic significance, whether or not they are metabolic precursors of vitamin A. 

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