Dynamics of precipitation of casein with carbon dioxide

Carbon dioxide is a green alternative for mineral acids (e.g., sulphuric acid) in protein precipitation. The precipitation using a gaseous precipitant differs from the conventional precipitation in the way and the rate at which the precipitant can be applied to the aqueous solution. In this paper, the consequences of using carbon dioxide were investigated for the precipitation of the milk protein casein. Product properties, such as particle size, solids content and calcium release were investigated in a batch system at various mixing conditions and gas addition rates. In addition, mass transfer coefficients were determined from pH response data. The experiments revealed a strong influence of stirring rate and gas flow rate on the particle size. The main effect of varying the gas flow was through the change of acidification rate, much alike precipitation with sulphuric acid. At high acidification rates, the particle size of casein precipitated with carbon dioxide was smaller than with sulphuric acid.