Selective precipitation is a common method for the isolation of β-casein, using the different calcium sensitivities of the individual caseins and the selective solubility of β-casein at a low temperature. In previous studies, it has been indicated that the β-casein yield depends on the physicochemical characteristics of the casein raw material used for fractionation. The objective of this study was to evaluate and compare the solubility of α(S)- and β-casein in solutions of micellar casein, sodium caseinate, and calcium caseinate as a function of pH and temperature. Additionally, the solubility of isolated α(S)- and β-casein fractions in demineralized water, ultrafiltration permeate, and a calcium-depleted milk salt solution was investigated depending on the pH and temperature. Furthermore, micellar casein, sodium caseinate, and calcium caseinate were subjected to a calcium chloride-precipitation process to determine the solubility of α(S)- and β-casein in calcium chloride precipitate, which is produced during selective precipitation, as a function of temperature and pH. Generally, the temperature had only a marginal influence on the α(S)-casein solubility compared with the β-casein solubility, whereas the solubility was shown to be strongly influenced by the pH. Our results suggest that the yield of β-casein obtained during isolation by means of selective precipitation may be a result of the solubility characteristics of α(S)- and β-casein in calcium chloride precipitate. Manufacturers may consider a simple solubility experiment before the β-casein isolation process by means of selective precipitation to predict β-casein yield.

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For the application of functional peptides in innovative products, these peptides have to be individually available. This may be accomplished by a well‐considered combination of a pure protein precursor, a selective cleaving enzyme, and an advanced separation technology. In this proof‐of‐principle approach, micellar casein and β‐casein were subjected to tryptic hydrolysis and the generated casein peptides were identified and characterised. The basic target peptides, β‐casein f(177‐183) and β‐casein f(170‐176), were then enriched. A permeate containing 35% of the target peptides was produced after two‐stage ultrafiltration of micellar casein tryptic hydrolysate. In comparison, enrichment up to 58% was achieved starting from β‐casein tryptic hydrolysate.