Abstract
1. Nitrogen distribution in Japanese mother's milk was determined. The concentrations of crude protein (N×6.38) varied similar to previous data with the progress of days after parturition.
2. The proportion of casein nitrogen against total nitrogen is as follows: human milk I (1-10days after parturition) 8.9%; human milk II (10-115 days after parturition) 37.0%; bovine milk 78.0%.
3. The proportion of milk serum protein nitrogen against total nitrogen is as follows: human milk I 60.5%; human milk II 39.3%; bovine milk 16.9%.
4. The proportion of non-protein nitrogen against total nitrogen is as follows: human milk I 30.6%; human milk II 23.7%; bovine milk 5.1%.
5. In both human and bovine milk, the concentrations of urea, creatine, amino sugar and free amino acid as a major non-protein nitrogenous compounds were determined and the proportion of their nitrogen against total nitrogen or non-protein nitrogen was estimated. Human milk contained more amino sugar and free amino acid compared with bovine milk.
6. True protein levels or accurate nitrogen-to protein factors should be used for accurate estimates of nutritive value of foods like human milk containing much non-nitrogenous compounds.
