Date of Award:
Master of Science (MS)
Nutrition, Dietetics, and Food Sciences
Department name when degree awarded
Nutrition and Food Sciences
Rodney Jay Brown
Rodney Jay Brown
The purpose of this study was to develop a short, easy procedure to measure five major proteins in milk and to detect concentrations of added protein to dairy products. Combinations of casein or whey protein with nonfat-dry milk were made with concentration ratios from 0:10 to 10:0. Similar mixtures of defatted goat milk with defatted cow milk were prepared. Samples were hydrolyzed in 6 N HCl at 145°C for 4 h and analyzed for amino acid composition. Multiple regression equations were derived to estimate the relative content of whey protein or casein added to nonfat-dry milk and goat milk added to cow milk employing amino acid profiles of whey protein, casein, nonfat-dry milk, goat milk and cow milk. Correlation coefficient values were all greater than .99. Measuring individual concentrations of milk proteins required separating casein and why proteins by reverse phase high performance liquid chromatography on a C3 column. αs-, β-, and κ-casein were separated after dissociating casein micelles with mercaptoethanol and urea. A 40:60 to 0:100 gradient of .15 M sodium chloride/triethylamine (pH 2.5) and 40% acetonitrile was used. Whey proteins, α-lactalbumin and β-lactoglobulin were separated with a 95:5 to 0:100 gradient of .15 M sodium chloride (pH 2.4) and acetonitrile. Eluted proteins were collected from the column, analyzed for purity by electrophoresis, and hydrolyzed in 6 N HCl at 145°C for 4 h. Purified proteins and mixtures of purified proteins were analyzed for amino acid composition. Estimates of individual protein concentrations in mixtures were made by solving simultaneous equations based on amino acid composition using a tektronix 4052 computer.
Walsh, Marie K., "Measurement of Proteins in Milk and Dairy Products" (1988). All Graduate Theses and Dissertations. 5360.
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