Changes in Distribution of Nitrogenous Fractions of Cheddar Cheese Whey During Ultrafiltration

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Abstract
Whey protein concentrates (over 80% protein, dry basis) were prepared from separated, pasteurized Cheddar cheese whey with 2 pilot scale, tubular ultrafiltration units. Analysis of samples from unpasteurized whole milk through all processing stages to production of spray-dried whey-protein concentrate indicated no significant protein denaturation in either unit. Evidence was obtained by a method of acid precipitation for determination of whey protein nitrogen, and visual corroboration was provided by polyacrylamide gel electrophoresis. Membranes in each unit were permeable to nonprotein nitrogen compounds, initial rejection coefficients for this fraction being .34 and .39. Approximately 10% of permeate nitrogen was precipitable in 12% trichloroacetic acid, indicating minor loss of protein and proteose-peptone fraction. Pre-ultrafiltration whey-nitrogen distribution was undenatured whey protein, 49.0; proteose-peptone, 17.2; and non-protein, 33.8%. After ultrafiltration to provide 87.5% protein (% nitrogen .times. 6.38) in retentate solids, corresponding whey-nitrogen distribution among these fractions was 82.5, 9.8 and 7.7%, respectively. There was little quantitative difference between fractionation performances of each unit.