Effects of potassium dichromate and sample storage time on fat and protein by Milko-Scan and on protein and casein by a modified Pro-Milk Mk II method.

A rapid procedure is described for measuring casein in milk by a combination of isoelectric precipitation and amido black dye-binding. Individual milk samples from 38 cows were subsampled, preserved with potassium dichromate at a concentration of 8 mg/ml of milk, and analyzed for fat and protein by the Milko-Scan 300 and for protein and casein by the dye-binding procedure on day 1, 4, 7, and 10 after milk collection. Fat tests were not affected by sample storage time, but protein tests showed variation depending on the interval between milk sample collection and analysis. In a separate study effects of potassium dichromate used as a preservative at 0, 2, 4, 6, 8, and 12 mg/ml of milk on chemical determinations were investigated. No changes were significant in fat and protein analyzed by the infrared method for concentrations of preservative. There were no significant differences in protein determination by the two methods for nonpreserved samples. For preserved samples, the dye-binding method for protein gave determinations higher than those by the infrared method. The difference increased linearly with increasing concentration of potassium dichromate at .07% in protein for every 2 mg of potassium dichromate per milliliter of milk.