THERMAL-BEHAVIOR OF WHEY-PROTEIN CONCENTRATE TREATED BY HEAT AND HIGHHYDROSTATIC-PRESSURE AND ITS FUNCTIONALITY IN WHEAT DOUGH

Solutions of commercial whey protein concentrate (CWPC, 82% protein) a t 5, 10, 20, and 30% were treated with heat at 90 degrees C or with hi gh hydrostatic pressure (HHP) at 85 Kpsi (Kpsi = 6.9 MPa) for 30 min. A CWPC solution at 20% also was treated far 30 min with heat at 60, 70 , 80, and 90 degrees C and HHP at 20, 40, 60, and 85 Kpsi. Differentia l scanning calorimetry (DSC) thermograms of untreated CWPC (82% protei n) showed two endothermic peaks: the first had an enthalpy value of 4. 72 J/g between 57 and 86 degrees C, and the second had an enthalpy val ue of 2.36 J/g between 120 and 143 degrees C. The first enthalpy peak disappeared after heat treatment at 90 degrees C for 30 min and HHP tr eatment at 85 Kpsi far 30 min, whereas the second peak remained, indep endent of concentration. The results indicate that HHP treatment cause d changes in the protein of CWPC, and the changes were comparable to t hose caused by high-temperature treatment. Differential scanning calor imetric analysis of CWPC, heat treated at 60 degrees C, showed an enth alpy value for the first peak of 3.34 J/g, approximate to 1.41 J/g low er than for untreated CWPC. A sharp decrease in enthalpy to 0.52 J/g f or the first peak was observed at 70 degrees C, with complete disappea rance at 80 degrees C. The second enthalpy peak was present at all tem peratures studied, with significantly higher enthalpy values at 90 deg rees C than at lower temperatures. DSC value for the first enthalpy pe ak for CWPC decreased significantly as HHP treatment level increased f rom 20 to 85 Kpsi. CWPC treated with HHP at 20 Kpsi had an enthalpy Va lue for the first peak that was approximate to 2 J/g higher than for t he untreated sample. It can be postulated that low HHP treatment of 20 % of CWPC solution for 30 min promotes the formation of covalent or no ncovalent cross-links and strong protein-protein interactions, hence t he higher enthalpy values. Scanning electron micrographs showed that s pray-dried, untreated CWPC was a globular form, whereas heat- and HHP- treated CWPC was a solid glasslike, porous or spongy form. Incorporati on of 10% untreated CWPC into wheat flours decreased mixograph water a bsorption, extended mixing time, and caused rapid breakdown of gluten after optimum dough development. Incorporation of 10% heat- or HHP-tre ated CWPC significantly increased mixograph water absorption and exten ded mixing time compared to the control but decreased mixing time comp ared to dough fortified by untreated CWPC. Mixing tolerance of dough w as restored by both heat- and HHP-treated CWPC.