Nitrogen-to-protein conversion

A nitrogen-to-protein conversion factor (N-factor) of 6.25 is commonly used for animal feeds and other materials. The practice of using 6.25 as an V-factor is based on an incorrect assumption that protein in a given material contains 16 percent nitrogen (100/16 = 6.25).126... 

Tkachuk, R., Calculation of the nitrogen-to-protein conversion factor. In Nutritional Standards and Methods of Evaluation for Food Legume Breeders., J. H. Hulse, K. O. Rachie and L. W. Billingsley. Lanham, Beman... 

Mosse, J., Nitrogen to protein conversion factor for 10 cereals and 6 legumes or oilseeds—a reappraisal of its definition and determination—Variation according to species and to seed protein content. Journal of... 

Lourenco, S., Barbarino, E., Marquez, U., and Aidar, E. (1998). Distribution of intracellular nitrogen in marine microalgae Basis for the calculation of specific nitrogen to protein conversion factors. J. Phycol. 34, 798-811. 

Fujihara, S., Kasuga, A., and Aoyagi, Y., Nitrogen-to-protein conversion factors for common vegetables in Japan, J. Food Sci., 66, 412, 2001. 

Sosulski, F.W. and Imafidon, G.I., Amino acid composition and nitrogen-to-protein conversion factors for animal and plant foods, J. Agric. Food Chem., 38, 1351, 1990. 

Lorengo, S. O., Barbarino, E., De-Paula, J. C., Otavio da Pereira, L. S., and Marquez Lanfer, U. M. (2002). Amino acid composition, protein, protein content and calculation of nitrogen-to-protein conversion factors for 19 tropical seaweeds. Phycol. Res. 50, 233-241. 

Tkachuk, R. 1969. Nitrogen-to-protein conversion factors for cereals and oilseeds meals. Cereal Chem., 46, 419 23. 

Both the assumptions are unsound. Different food proteins have different nitrogen contents and, therefore, different factors should be used in the conversion of nitrogen to protein for individual foods. Table 13.1 shows the nitrogen contents of a number of common proteins, together with the appropriate nitrogen conversion... 

In free heme molecules (heme not bound to protein), reaction of oxygen at one of the two open coordination bonds of iron (perpendicular to the plane of the porphyrin molecule, above and below) can result in irreversible conversion of Fe2+ to Fes+. In heme-containing proteins, this reaction is prevented by sequestering of the heme deep within the protein structure where access to the two open coordination bonds is restricted. One of these two coordination bonds is occupied by a side-chain nitrogen of a His residue. The... 

Table B1.2.1 Conversion Factors from Percent Nitrogen to Percent Total Protein for Various Commodities and Their Products...

Amino acids derived from dietary or body proteins are also potential fuels that can be oxidized to acetyl CoA, or converted to glucose and then oxidized (see Fig. 2). These oxidation pathways, like those of fatty acids, generate NADH or FAD(2H). Ammonia, which can be formed during amino acid oxidation, is toxic. It is therefore converted to urea in the liver and excreted in the urine. There are more than 20 different amino acids, each with a somewhat different pathway for oxidation of the carbon skeleton and conversion of its nitrogen to urea. Because of the complexity of amino acid metabolism, use of amino acids as fuels is considered separately in Section Seven, Nitrogen Metabolism. 

The total nitrogen content of the sample is determined after either reduction of all nitrogen to ammonia or liberation of all nitrogen as nitrogen gas. The crude protein content of the sample is derived from the ammonia/nitrogen content by use of appropriate conversion factors. In the case of meat and meat products, the factor 6.25 is used to convert ammonia/nitrogen to crude protein, on the basis that 16% of protein is nitrogen. 

The range of applications of potentiometric titrations for determination of acids and bases is very wide, as illustrated by the following examples. Carbonate, hydrogencarbonate, and hydroxide ions are all bases that can be titrated with a strong acid such as hydrochloric acid. The most popular method for determination of nitrogen, which is found in many important substances such as proteins, fertilizers, drugs, pesticides, natural waters, is the Kjeldahl method, based on the conversion of the bound nitrogen to ammonia, which is then separated by distillation and determined by titration with hydrochloric... 

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