Acidification of pressure-treated milk

The behaviour of reconstituted pressure-treated milk towards acidification with glucono-delta-lactone (GDL) was studied. After high-pressure treatment at 250, 450 or 600 MPa for 30 min, GDL was added for 20 h at 4 degrees C and soluble minerals, (1)H NMR relaxation rate and solvation changes with pH were studied, as well as the buffering properties of milk. Solubilization of calcium and phosphorus with pH, changes in (1)H NMR relaxation rate and solvation with pH were enhanced by the pressure treatment between pH 6.8 and 5.2. Between pH 6.8 and 6.1, the changes appeared to be independent of the pressure level, while between pH 6.1 and 5.2, they became dependent on the pressure level. The results are discussed in terms of pH and buffering changes due to the compression-decompression cycle. (C) 1997 Elsevier Science Ltd. All rights reserved.