Nitrogen-to-protein conversion factor

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... 

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

To estimate crude protein content of biomass or other materials, the nitrogen content of the material is measured by Kjeldahl or combustion methods and multiplied by a conversion factor where ... 

The vast majority, but not all, of the nitrogen in soy protein ingredients is of protein origin. The AOCS conversion factor for soybean protein is N x 5.71 however, industry practice is to label protein content as Protein (N x 6.25). Nitrogen may be deter-... 

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. 

In addition to inadequate separations by the Howe method, there is the further problem of the inadequacy of the conventional factor 6.25, which is generally applied to all fractions to convert from grams protein nitrogen to grams dried protein. The average nitrogen factor found experimentally in the dried proteins of pooled normal human plasma (5) is 6.73. The conversion factor of individual proteins (5) varies from 6.10 to 8.40. 

Besides the thorough biochemical investigation of a sample for its elemental composition or the fractions of the major components (carbohydrates, proteins, lipids) another way to derive biomass is to assume a proportionality between the nitrogen content of a sample and the amount of living matter. The chemical analysis of nitrogen which can be performed with a number of methods and an appropriate conversion factor (see above) then render the wanted amount of biomass. 

Since the most reliable protein nitrogen analysis (Table 3) gives a value of 157 mg N/g for albumin, conversion of N to albumin requires the factor 6.4. Convenient corresponding factors for N to globulin and total protein are 6.5 and 6.45, respectively. 

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