HIGH-PRESSURE EFFECTS ON THE COLLOIDAL CALCIUM-PHOSPHATE AND THE STRUCTURAL INTEGRITY OF MICELLAR CASEIN IN MILK - II - KINETICS OF THE CASEIN MICELLE DISINTEGRATION AND PROTEIN INTERACTIONS IN MILK

High pressure treatment results in a disintegration of micellar casein both in its native state and after UHT treatment when denatured whey proteins deposit on the casein micelles. Pressure treatments at lower temperatures lead to a stronger and quicker disintegration of micellar casein and to corresponding pH-value shifts. The pH-shift in UHT milk is higher than in pasteurized milk because of additional heat-induced insoluble calcium phosphate. At temperatures above 20 degrees C and p ressures above 200 MPa the pressure-induced denaturation of whey prote in superimposes this disintegration process which is, however, not the case in milk which already contains thermally denatured whey proteins . The degree of reversibility of pressure-induced shifts in pH and mic ellar size significantly differs between differently heat-treated milk s. In pasteurized milk, the shift in pH is nearly reversible whereas a considerable part of the shift in turbidity remains after 24 hours st orage at room temperature. In UHT milk the shift in turbidity is nearl y reversible but increase of the pH-value partly remains.