Isoelectric precipitation of casein using high-pressure CO₂

High-pressure CO₂ was used as a recyclable acid for the isoelectric precipitation of casein. Measurement of the pH during the high-pressure process allowed the comparison of the process with conventional precipitation using sulfuric acid. A simple model was made up to calculate the pH in complex aqueous solutions pressurized with CO₂. It was established that the isoelectric point (pH 4.6) could not be reached with CO₂, unless the milk was diluted. Nevertheless, high precipitation yields could be obtained with this process. Still, it was found that the precipitation is mainly caused by the decrease in pH. The removal of calcium phosphate appeared to be complicated, probably because of precipitation of calcium phosphate in the casein-free solutions after the pressure is released.