EFFECT OF TREATMENT BY GASEOUS CARBON-DIOXIDE ON THE COLLOIDAL PHASE OF SKIM MILK

Treatment of milk by injection of CO2 and depressurization was studied for the effect on milk salts and on the buffering properties of skim milk in order to correlate them to mineral balance. Injection of CO2 b y pressure decreased the pH of milk. After depressurization, pH return ed to its initial state. No changes were observed in the concentration s of inorganic P, Ca, or Mg in the aqueous phase, determined after ult racentrifugation, but the buffering curves of depressurized milk that had been treated with CO2 were different from those of the original mi lk. For the initial milk, two buffering peaks at pH 4.95 and 5.40 were observed instead of one, showing that the solubilization of CO2 induc ed the formation of a new salt system. When CO2 pressure increased, th e buffering value at pH 4.95 decreased; solubilization occurred for th e inorganic calcium phosphate and the Ca directly bound to caseins. Th e 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, w hich was changed into other salt forms.