Variability of Casein, Serum Protein and Nonprotein Nitrogen in Plant Milk Supplies in Ontario

Abstract

Weekly milk samples from 24 selected dairy plants in Ontario were analyzed for protein for 12 months in 1971 and early 1972. Samples from selected dairy plants proportionally represented the industrial milk production of eastern, southern and northern Ontario. The data showed a significant difference in amounts of casein, whey protein and non-protein nitrogen between milks from different areas as well as between seasons. There was also a significant difference in the expected composition of the total protein in the Ontario milk supply and these results. Historically, protein components are for casein 76.6%, serum protein 18% and nonprotein nitrogen 5.5%. Results for protein were 74.76% casein, 19.1% serum protein, and 6.16% nonprotein nitrogen. Eastern Ontario had the lowest casein and the highest serum protein, followed by northern Ontario and southern Ontario respectively. The highest casein occurred in January and February, 77.08 and 77.19% with the lowest standard deviations of ± 2.36 and ± 2.28. This coincided with the lowest serum protein of 17.98 and 17.79% with the lowest standard deviations of ± .97 and ± 1.18. Casein fluctuated most in May with a standard deviation of ± 5.89%. The lowest casein occurred in August, September, and October, 73.41, 73.07 and 73.09%. This coincided with the highest nonprotein nitrogen of 6.99, 7.59 and 7.09%. © 1973, American Dairy Science Association. All rights reserved.