Determination of Whey Protein Denaturation in Heat-Processed Milks: Comparison of Three Methods

Fast protein liquid chromatography was used to determine the extent of whey protein denaturation in various heattreated milk samples: Sordi-indirect UHT (145C/3 s), Dasi-direct UHT (142C/3 s), HTST (80C/30 s), and batch (63C/ 30 min). Results were compared with other published methods (differential scanning calorimetry, whey protein nitrogen index, and Kjeldahl nitrogen on salt fractions). Results of the differential scanning calorimetry method were too erratic to be used to quantify whey protein denaturation. The remaining methods (fast protein liquid chromatography, Kjeldahl nitrogen, and whey protein nitrogen index) gave reproducible results and the extent of denaturation (highest to lowest) was consistently predicted as Sordi > Dasi > HTST > batch. There was no difference between fast protein liquid chromatography and Kjeldahl nitrogen, but there was a significant difference between fast protein liquid chromatography and whey protein nitrogen index and between Kjeldahl nitrogen and whey protein nitrogen index. Fast protein liquid chromatography appears to be an effective method to determine whey protein denaturation in heat-treated milks.