PHYSICAL-PROPERTIES OF COLD-SETTING GELS FORMED FROM HEAT-DENATURED WHEY-PROTEIN ISOLATE

Cold-setting gels were formed from a 100 g kg-l whey protein isolate (WPI) solution (pH 7.0) which had been heated to 90 degrees C for 30 min in the absence of salt. Heating caused the globular protein molecules to unfold and form linear aggregates, but electrostatic repulsion opposed extensive protein-protein interactions and so prevented gel formation. When the solution containing heat-denatured proteins was cooled to room temperature and mixed with NaCl (0.2 mol kg(-1)), the electrostatic charges were shielded and a gel formed. The rate of gel formation increased on cooling, which suggests that the major driving force for protein aggregation and gelation is the hydrophobic effect. Once formed, the rigidity of the gels decreased with decreasing temperature, which suggested that non-hydrophobic forces (eg configurational entropy, hydrogen bonding, van der Waals forces and disulphide bond formation) are more important in determining the final gel rigidity. The turbidity and rigidity of gels formed by adding salt to preheated WPI at room temperature were less than those of gels formed by heating WPI in the presence of salt. The ability of WPI to form cold-setting gels with relatively low turbidity extends the range of applications of whey proteins as functional ingredients in the food industry.