Repeatability and Accuracy of Dye-Binding and Infra-Red Methods for Analyzing Protein and Other Milk Components 1

Abstract

Udy and Pro-Milk Mark II dye-binding methods and the Milko-Scan 104 infra-red device were evaluated for accuracy and repeatability in the analysis of protein in raw milk supplies. The infra-red device was also evaluated for accuracy in determination of milkfat, lactose and solids-not-fat, and was compared with the Milko-Tester for fat analysis. Repeatability of the three methods was, in all instances, less than 0.05% for protein. Standard deviation of accuracy (σ_y,x) for protein (total nitrogen × 6.38) for the Udy Analyzer, Pro-Milk, and Milko-Scan units was 0.063, 0.062, and 0.067, respectively. Standard deviation of accuracy of the Milko-Scan rated against Mojonnier and Milko-Tester methods for milkfat was, respectively, 0.054 and 0.050. Compared with liquid chromatography lactose determination and Mojonnier solids-not-fat determination, the Milko-Scan showed a standard deviation of accuracy of 0.083 and 0.073, respectively.