An Improved Procedure for the Determination of Milk Proteins by Dye Binding

Abstract

The precision of the Orange G dye binding method has been increased by a method for measuring the concentration of dye not bound by the milk proteins. The results of 345 comparisons of protein determined by the new method with that determined by the macro-Kjeldahl showed a correlation coefficient of 0.98, with a standard deviation from regression of 0.078% protein. When the protein contents of the milk from individual cows of 6 different breeds were determined by the 2 methods, covariance analysis showed no significant breed difference. From 224 duplicate determinations it was observed that 19 out of every 20 single determinations fell within 0.06% protein of the average for duplicate readings. Large variations in the amounts of butterfat and lactose were found to be without effect on the protein values determined by dye binding. The only preservative found suitable for use in raw milk at room temperature was mercuric chloride. The mixture of 1.5 ml of milk with 25 ml of dye solution was stable for 2 weeks at room temperature.