Characterisation of pressure-treated skimmed milk powder dispersions: application of NMR spectroscopy

Skimmed milk powder (SMP) (bovine) and skimmed milk powder/sucrose dispersions before, during and after high-pressure treatment have been studied by nuclear magnetic resonance (NMR) spectroscopy (principally P-31). The P-31 spectra of samples at 293 K before and after pressure (400–600 MPa) treatment were not significantly different from one another, whether or not sucrose was present. This indicates that physicochemical changes relating to phosphorus-containing components occurring during a pressure cycle are either reversible or result in re-immobilisation, while protein components may be rearranged. The P-31 NMR spectra of these dispersions at 293 K under pressure (100–300 MPa) showed that pressure caused a considerable increase in the free inorganic phosphate concentration and that the increase was proportional to the magnitude of pressure. Decompression to ambient caused an exact reversal of this trend. These findings are discussed in terms of characterisation and properties of pressure-treated SMP dispersions by other methods and techniques.