Buffer properties of milk treated with high pressure carbon dioxide

The buffering properties of milk at 38 degrees C treated with CO2 at pressu res up to 13.8 MPa were determined. Buffer index was determined directly fr om the pressurization data by assuming a strong acid equivalent for each ad dition of CO2. Milk treated with CO2 showed buffering peaks at pH 5.2 and p H 4.95, which is indicative of the presence of various salt systems based o n the interactions of calcium, phosphate, and bicarbonate. Milk treated wit h HCl showed a single buffering peak at pH 5.05. The refractive index (RI) as a function of pH was used to compare micelle a ggregation with either addition of CO2 or HCl to milk. The results showed t hat extent of precipitation as a function of pH agreed for both precipitant s. However, the point that corresponds to solubilization of colloidal calci um phosphate (CCP) for the CO2 treated milk was shifted approximately .2 pH units higher than the HCl treated milk, possibly because of pressure effec ts on solubilization of CCP.