Essential amino acid index

The protein concentration and amino acid composition of sunflower meal also vary with the source of seed, and high-temperature processing may have a deleterious effect on its lysine content. Generally, however, sunflower meal exhibits a well-balanced amino acid composition with an essential amino acid index of 68, compared to 79 for soybean meal and 100 for whole egg (35). 

In view of the low protein content of the diet in some countries, it is of paramount importance to be able to evaluate the biological efficiency of a given protein. To express this property mathematically for each protein, one can determine the essential amino acid index, which is the geometric mean of the ratio of the amino acid in the test protein versus the amino acid in a standard protein most efficiently utilized (egg protein). On the basis of the amino acid index, an equation was developed which expresses the biological value of the protein. 

Oser, B.L. An integrated essential amino acid index for predicting the biological value of proteins. In Protein and amino acid nutrition 66. (Albanese, A.A., ed.). New York Academic Press 1959... 

Biological value is stated as the proportion of the nitrogen intake that is actually retained and takes account of endogenous urinary and faecal nitrogen, whereas chemical score and the essential amino acid index are based on the proportion of the main limiting amino acid of the protein in relation to that in a standard protein. 

Proteins have different biological availabilities in the human body and a number of methods have been introduced to evaluate and measure protein utilisation and retention. Two types of measurements are used to estimate protein quality biological assays and chemical analysis. The most common measures of protein quality included Biological Value (BV), Protein Efficiency Ratio (PER), Net Protein Utilisation (NPU), Amino Acid Score (AAS also known as chemical score, CS), Essential Amino Acid Index (EAAl) and Protein Digestibility Corrected Amino Acids Score (PDCAAS), amongst other procedures and modifications. 

Protein hydrolysis in 6N HCl and subsequent analysis to determine amino acids (except tryptophan, which is acid labile) chemically present is a first step in protein quality evaluation. The chemical score and the EAA index represent attempts to use this information to chemically estimate nutritional quality of protein their obvious limitation is their disregard for amino acid availability. The chemical score is obtained by evaluating the percent of the limiting amino acid in comparison to that amino acid in whole egg protein ). The EAA index is the geometric mean of the ratios of each of the essential amino acids to those amino acids occurring in whole egg (4). 

In spite of this fact, in most studies, amino acid score (AAS), index of essential amino acid, and egg protein have been applied. Seaweeds have usually low AAS (about 20-67%) nevertheless, it is common similarly to other plants (Matanjim et ah, 2009). Matanjim et al. (2009) showed that Sargassum polycystum had AAS higher (67%) than soybeans (47%) or casein (58%) and then this value could be compared with beef (69%). 

This is the geometric mean of the egg, or standard pattern, ratios of the essential amino acids. It has the advantage of predicting the effect of supplementation in combinations of proteins. On the other hand, it has the disadvantage that proteins of very different amino acid composition may have the same or a very similar index. 

The use of plasma amino acid levels as an index of nutritive status has been extensively explored (see review by Munro, 1970). Characteristic changes are seen in established protein malnutrition, there being a fall in the levels of most essential amino acids, combined with a rise in the levels of several non-essential amino acids. 

Refractive Index of Protein from Amino Acid Composition. The method used for calculating the refractive index of a protein from its amino acid composition is essentially the same as that described by Cohn and Edsall (9, Chap. 16) for calculating the specific volume of a protein from its amino acid composition. 

B, Plots of Tj versus fx, the mole fraction of pentamers containing guest residues, are essentially linear to fx = 0.5. Extrapolation to the value of Tj at fx = 1 is used to provide an index of the relative hydrophobicities of the amino acid residues. This provides for a hydrophobicity scale which is based on the hydrophobic folding and assembly of interest. Adapted with permission from Urry, 1993a. 

The most frequent application of precolumn derivatization is in amino acid analysis. Here, the amino acids are derivatized for instance with 9-fliiorenyl methoxycarbonyl chloride (FMOC) or o-phthalaldehyde (OPA) to form strongly fluorescing compounds, which can be detected easily with a fluorescence detector [93], [94], Another typical application for precolumn derivatization is in the analysis of fatty acids. Fatty acids have no chromophore, so UV detection is impossible. Even highly unsaturated fatty acids can be detected only in the very far UV range (< 200 nm) with poor sensitivity. Other detectors, such as the refractive index detector, have a disadvantage because they cannot be used in gradient elution, which is essential for fatty acid analysis. Therefore, the fatty... 

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