Chemical fractionation of caseins by differential precipitation: influence of pH, calcium addition, protein concentration and temperature on the depletion in α‐ and β‐caseins

Summary The impact of pH, calcium and casein concentrations, and temperature on the efficiency of the differential precipitation of caseins by calcium affinity was investigated, using native phosphocaseinate as starting material. We adapted one of the most recent methods for the separation of caseins that is based on the addition of calcium at alkaline pH. Increasing the pH to 11 disturbed the micellar structure by enhancing electrostatic repulsion of caseins, leading to a marked viscosity increase and a significant particle size decrease, indicating casein micelle disruption. This pH‐driven increase in negative charges enhanced the affinity of individual caseins for calcium, proportionally to the number of phosphate groups carried by each casein. The addition of calcium first led to a progressive increase in the proportion of precipitated caseins, before reaching a plateau. Hence, an optimal calcium/casein molar ratio of about 40 was evidenced to optimise casein precipitation (and fractionation), leading to significant depletion of α‐casein (around 80%) and, in a lesser extent, β‐casein (around 65%) and κ‐casein (around 55%). This method led to relative proportions of caseins significantly differing from the starting material: 31% α‐casein, 45% β‐casein and 24% κ‐casein.