Solubility of the main proteins in 10 x acid and rennet whey retentates was studied in the pH range 2.0 to 4.0 in the presence of NaCl from 2 to 15% (w/v) final concentration, at 20°C to find fractionation conditions suitable for preparing pure P-lactoglobulin and P-lactoglobulin-free whey proteins and scaling up. At pH 2.0, 7% NaCl, 20 min holding time, nearly all P-lactoglobulin remained soluble while a precipitate (Pl) containing all other proteins was formed. Pure P-lactoglobulin was quantitatively recovered by salting-out the centrifugation supernatant at 30% NaCl (w/v) final concentration. Pl, insoluble at pHs lower than 4.0, was made soluble at any pH by dissolving at pH 9.0, dialyzing against 50 mM formic acid (pH 3.0) and freeze-drying.
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