Stability of casein micelles subjected to CO2 reversible acidification: Impact of carbonation temperature and chilled storage time

Physicochemical properties of non-fat, low heat, reconstituted skim milk subjected to pH cycling using CO2 as an acidifying agent were studied. The pH was dropped to 5.5 at 4 °C for 15 min and temperature was subsequently kept at 4 °C or increased to 20 and 30 °C for further 45 min, before degassing under vacuum. Even though many overall properties of the micelles were not affected (calcium and protein content, size, zeta potential, acid gelling properties), it was shown that the internal organisation of the micelles did change. The structure of the micelle was dependent on carbonation temperature and evolved during chilled storage, as indicated by the rennet clotting time and micelle hydration variations. In contrast, modifications of the micellar calcium phosphate salt form, as reflected in the buffering capacity curves, did not depend on temperature of carbonation.