β-Casein as a bioactive precursor - processing for purification.

β-casein can be regarded as a precursor for different peptides with a biological activity, such as antihypertensive, opioid, or immunomodulating activities, which are released from the protein by digestion or enzymatic hydrolysis in a technological process. Meeting the demand for highly purified β-casein, a method for small pilot-scale isolation of β-casein from micellar casein powder was developed. The objective was to maximise both, yield and purity of β-casein by constructing a set of experiments at laboratory scale in which relevant factors pH-value, CaCl 2 -concentration, temperature, and β-casein solubilisation time were varied simultaneously. Increased pH-value, solubilisation time, the interaction of pH-value and temperature as well as a decreased reconstitution temperature caused a significant (p<0.05) higher yield, whereas β-casein purity increased with decreasing solubilisation time. Optimisation of both responses was achieved at pH 11, a CaCl 2 -concentration of 50 mmol/l, a reconstitution temperature of 30°C, and a solubilisation time of 2 hours. A purity of 95%, a 15% yield of β-casein, and a recovery of 33% of total p-casein, determined by reversed-phase high performance liquid chromatography was achieved. Transferring the optimised extraction method from laboratory to small pilot-scale, a comparable yield (14%) and purity (90%) of the produced food-grade β-casein was obtained. The p-casein yield could be increased to 24% (53% recovery of total p-casein), accepting a purity of 77%.