Abstract
The use of reversed-phase HPLC for the determination of whey protein denaturation was investigated. Denatured whey proteins and caseins were isolated from undenatured whey proteins by isoelectric precipitation at pH 4.6. Whey protein denaturation was determined by comparing reversed-phase HPLC protein profiles of isolates far heat-treated and unheated NDM from pooled herd, Holstein cows. In general, protein profiles for heat-treated skim milk indicated that whey protein denaturation began at about 40°C, became more rapid at 70°C, and was 95% complete at 85°C. Undenatured whey protein was also quantified as whey protein nitrogen based on their absorbance and nitrogen content compared with known whey protein standards or by augmenting the same samples with a known amount of lysozyme. Whey protein nitrogen values obtained by the reversed-phase HPLC method were in good agreement with those obtained by the modified Kjeldahl nitrogen procedure for three NDM powders prepared from skim milk preheated to 63, 74, and 85°C before spray drying, and by commercial low and high heat NDM standards. Isolation of undenatured whey proteins and their separation by reversed-phrase HPLC takes approximately 1.5h.
Published Version
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