A COMPARATIVE RHEOLOGICAL STUDY OF HEAT AND HIGH-PRESSURE INDUCED WHEY-PROTEIN GELS

The theological properties of whey protein concentrate (WPC) gels induced by high pressure (4000 bar/30 min), were compared to those induced by heat (80 degrees C/30 min) at protein concentrations ranging from 110 up to 183 g/liter. Oscillation measurements at 1 Hz and 0.001 strain showed the highest storage and loss moduli for heat set gels, while creep experiments at a stress level of 40 Pa gave larger sample deformations for high pressure induced gels. Relaxation experiments performed at 17 and 33% deformation were characterized by a higher force decay as a function of time for the high pressure gels, while during compression the compression modulus was always higher in the case of heat set gels. Electron microscopy showed a higher level of cross links in the heat induced gels; high pressure generated a more porous network with a lower amount of intermolecular cross links.