Casein nitrogen content

The nitrogen content of milk is distributed among caseins (76%), whey proteins (18%), and NPN (6%). This does not include the minor proteins and glycoproteins that are associated with the fat globule membranes (FGM). This nitrogen distribution can be determined by the Rowland fractionation [85] method given in Table 3.12. 

Schmidely P, P. Morand-Fehr and D. Sauvant, 1997. Effects of genetic variant for alphaSl casein and diet nitrogen content on the response of some plasma characteristics after alanine infusion in early and mid lactation goats. Options Mediterraneennes, Series A, 155-158. 

Walter et al. (38) measured the protein efficiency ratio (PER) of flour prepared from sweet potatoes which were cooked in a drying oven. Because the PER is determined on the basis of a diet containing 10% protein, the Jewel and Centennial sweet potatoes used in this study were stored until sufficient starch had metabolized to increase crude protein content to 11.25% (dry basis). When the flour was fed to Sprague-Dawley strain rats, the corrected PER values were 2.22 and 2.00 for Centennial and Jewel cultivars, respectively, compared to 2.50 for casein. Centennial had the highest PER value of the two cultivars because its NPN content was lower. The net effect of increased NPN content is to lower the amount of essential amino acids as a percentage of the total nitrogen and thus decrease the PER value. 

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