Effect of Treatment by Gaseous Carbon Dioxide on the Colloidal Phase of Skim Milk

Abstract

Treatment of milk by injection of CO2 and depressurizationwas studied for the effect on milk salts andon the buffering properties of skim milk in order to correlate them to mineral balance. Injection of CO2 bypressure decreased the pH of milk. After depressurization,pH returned to its initial state. No changes were observed in the concentrations of inorganic P, Ca, or Mg in the aqueous phase, determined after ultracentrifugation, but the buffering curves of depressurized milk that had been treated with CO2 were different from those of the original milk. For the initial milk, two buffering peaks at pH 4.95 and 5.40were observed instead of one, showing that the solubilization of CO2 induced the formation of a new salt system. When CO2 pressure increased, the buffering value at pH 4.95 decreased; solubilization occurred for the inorganic calcium phosphate and the Ca directly bound to caseins. The second buffering value at pH 5.40 increased as new salts were formed. Higher pressures shifted the pH of maximal buffering from pH 4.95 to 4.75 and from pH 5.40 to 5.05. The CO2 had a reversible effect on pH and an irreversible effect on inorganic colloidal calcium phosphate, which was changed into other salt forms.