Determination of the whey protein index in milk protein concentrates

Milk protein concentrates are common ingredients in the dairy industry, with varying processing histories and composition. The objective of this research was to determine the feasibility of using the whey protein nitrogen (WPN) index, a well-established index for skim milk powder and nonfat dry milk, as a quality parameter for milk protein concentrates. The WPN index is a value based on the moisture-adjusted weight of skim milk powder. We hypothesized that WPN, even when standardized based on protein, may change depending on solubilization conditions of milk protein concentrates because of differences in solubilization conditions or processing history. The WPN was measured for model concentrates with different thermal history or reconstitution conditions. The WPN was not affected by an increased concentration of soluble casein in the dispersions nor after solubilization of the powder at 22 or 60 degrees C. All reconstituted samples were standardized for protein. The WPN was also in full accordance with residual native protein measured by chromatography.