Factors Affecting Measurement of Undenatured Whey Protein Nitrogen in Dried Whey by a Modified Harland-Ashworth Test

Abstract The Harland-Ashworth test for measuring undenatured whey protein N in NDM was modified to measure undenatured whey protein N in dried whey. Dried whey was reconstituted in phosphate buffer (pH 6.7) then saturated with NaCl and incubated for 30min at 37°C. Samples were cooled to room temperature and filtered before total absorbance was measured at 280nm. Absorbance measurements were taken at 280nm to prevent difficulties caused by turbidimetric measurements in Harland-Ashworth filtrates. Nonprotein absorbance was measured on TCA deproteinized filtrates and subtracted from total absorbance values to find absorbance of undenatured whey protein. The modified assay produced reproducible estimates of undenatured whey protein in NDM as well as in dried whey. The correlation between absorbance of undenatured whey protein N and the corresponding Kjeldahl results were not influenced by season, heat treatment of samples, solids concentrations, residual milk-clotting enzymes, or pH of whey during heating.