Combined effects of thermal and pressure processing on food protein structure

Food proteins are affected significantly when processed in terms of temperature, holding time and pH. Their combined effects together with temperatures up to 75°C and pressures up to 100 MPa for the three proteins ovalbumin, β-lactoglobulin and lysozyme are reported. The examination of circular dichroism spectra revealed that the secondary and tertiary structure of the three proteins behaved differently when exposed to the processing conditions. β-lactoglobulin was the least stable protein at both pH7.0 and pH5.6 while lysozyme was the most stable protein being only marginally affected on a secondary structural level at pH 7.0. Although the higher pressures used in this study are recognized as being insufficient to impart the energy necessary to disrupt protein structure, when used in conjunction with temperature and holding time, the applied energy was found to be sufficient to disrupt the protein structure. It therefore appears that the processing conditions applied at specific pH act in combination to bring about structural change.