ABSTRACT
Solutions of commercial whey protein concentrate (CWPC, 82% protein) at 5, 10, 20, and 30% were treated with heat at 90°C or with high hydrostatic pressure (HHP) at 85 Kpsi (Kpsi = 6.9 MPa) for 30 min. A CWPC solution at 20% also was treated for 30 min with heat at 60, 70, 80, and 90°C and HHP at 20, 40, 60, and 85 Kpsi. Differential scanning calorimetry (DSC) thermograms of untreated CWPC (82% protein) showed two endothermic peaks: the first had an enthalpy value of 4.72 J/g between 57 and 86°C, and the second had an enthalpy value of 2.36 J/g between 120 and 143°C. The first enthalpy peak disappeared after heat treatment at 90°C for 30 min and HHP treatment at 85 Kpsi for 30 min, whereas the second peak remained, independent of concentration. The results indicate that HHP treatment caused changes in the protein of CWPC, and the changes were comparable to those caused by high-temperature treatment. Differential scanning calorimetric analysis of CWPC, heat treated at 60°C, showed an enthalpy value for the first peak of 3.34 J/g, ≈1.41 J/g lower than for untreated CWPC. A sharp decrease in enthalpy to 0.52 J/g for the first peak was observed at 70°C, with complete disappearance at 80°C. The second enthalpy peak was present at all temperatures studied, with significantly higher enthalpy values at 90°C than at lower temperatures. DSC value for the first enthalpy peak for CWPC decreased significantly as HHP treatment level increased from 20 to 85 Kpsi. CWPC treated with HHP at 20 Kpsi had an enthalpy value for the first peak that was ≈2 J/g higher than for the untreated sample. It can be postulated that low HHP treatment of 20% of CWPC solution for 30 min promotes the formation of covalent or noncovalent cross-links and strong protein-protein interactions, hence the higher enthalpy values. Scanning electron micrographs showed that spray-dried, untreated CWPC was a globular form, whereas heat- and HHP-treated CWPC was a solid glasslike, porous or spongy form. Incorporation of 10% untreated CWPC into wheat flours decreased mixograph water absorption, extended mixing time, and caused rapid breakdown of gluten after optimum dough development. Incorporation of 10% heat- or HHP-treated CWPC significantly increased mixograph water absorption and extended mixing time compared to the control but decreased mixing time compared to dough fortified by untreated CWPC. Mixing tolerance of dough was restored by both heat- and HHP-treated CWPC.
