The Protein and Non-Protein Nitrogen Fractions in Milk. II. Their Content in Fresh Raw Milk

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Abstract
Using the methods described in a previous paper (10), t)ie protein and non- protein nitrogen fractions were studied in fresh raw milk from individual cows and from a pooled milk supply. EXPERIMENTAL RESULTS Table 1 presents the analyses of six milk samples from individual cows. All the cows were young, in good health, and .in the gen.eval middle range of the lac- tation period. Their milk yield ranged from 11 to 54 lb. per day. Thesamples were correct composites of evening and morning milkings. In addition to the individual cow samples of table 1, samples from single milkings from eight other cows were analyzed incidental to other phases of the general project. Table 2 gives the range and average for all of the nitrogen fractions in milk as found in all of the individual cow samples. Fresh mixed milk samples, taken from the supply as received commercially by the Department of Dairy Industry, were analyzed in various phases of the work. Table 3 gives the range and average values for the nitrogen fractions as found in !4 such milk samples. The values show variations of .considerable magnitude. The average figures for casein nitrogen as percentage of the total nitrogen are in good agreement with the figures reported in the literature. Davies (2) found casein.nitrogen to account for 76.7 per cent of the total nitrogen, Golding et aL (5)have reported 76.5 per cent, and Rowland (9) 78.7 per cent in the individual and 78.3 per cent in bulk milk samples. In the present study casein nitrogen accounts for 76.6 per cent of the total nitrogen in the individual and 78.9 per cent in the mixed milk samples. The average albumin content was 0.23 per cent in the individual and mixed milk samples and the globulin content was 0.21 and 0.14 per cent in the individual and. mixedmilk samples, respectively. The combined albumin and globulin content was 0.44 per cent in the individual and 0.37 per cent in the mixed milk samples, as compared to 0.55 to 0.70 per cent heat coagulable proteins as fre- quently reported in the literature. This difference likely is due to methods em- ployed. The higher values probably ~ the result of reporting as "albumin," all of the heat-eoagt~lable proteins obtainable from the serum after removal of casein. It is probable that proteoses are included to some extent. The .values for albumin and globulin reported in this study, however, are in harmony with
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