Quantitation of the major whey proteins in human milk, and development of a technique to isolate minor whey proteins

Abstract

Several whey proteins of human milk have important nutritional and physiological roles for the breast fed infant. Only 75 to 85% of the proteins in whey have been identified and quantitated, leaving a remaining protein fraction containing many proteins of probable nutritional and physiological significance. In this study, colostrum and mature milk samples were collected, and the concentrations of five major whey proteins were measured using immunoelectrophoresis or immunodiffusion. Based on Kjeldahl nitrogen analysis, the total concentration of whey proteins in colostrum was 17.05 mg/ml and in mature milk 5.95 mg/ml. The concentration of α-lactalbumin was 3.7 mg/ml and 1.7 mg/ml in colostrum and mature milk, respectively; lactoferrin concentration was 7.3 and 1.5 mg/ml; and secretory IgA concentration was 4.7 and 1.2 mg/ml. In both colostrum and mature milk, concentrations of serum albumin and lysozyme were 0.37 and 0.07 mg/ml, respectively. The sum of these major whey proteins expressed as a percentage of the total whey protein accounted for 81% of mature whey protein, and 94% of colostral whey protein, leaving 19% and 6% in the remaining protein fraction. A method was developed to isolate this remaining protein fraction from the major whey proteins using gel filtration and immunoaffinity chromatography. The quantitatively minor whey protein fraction obtained was further characterized using polyacrylamide gel electrophoresis and ion exchange chromatography.