Casein as a Modifier of Whey Protein Isolate Gel: Sensory Texture and Rheological Properties

The objective of this study was to determine if casein could be used to adjust the structure of whey protein gels and alter targeted textural properties. Secondarily, we sought to determine if specific structural and mechanical properties were associated with sensory texture terms. Heat set gels were made from whey proteins alone or combined with casein in micellar or dispersed form at pH 6.0 and 5.5. Replacing the whey protein with casein produced a gel breakdown pattern that was more cohesive during mastication with increased moisture retention. Additionally, casein addition reduced gel strength but minimally altered recoverable energy (an indicator of elasticity). Structural breakdown patterns were shifted from brittle- to ductile-like fracture for gels containing dispersed casein at pH 5.5 or micellar casein at pH 6.0. Shifts in microstructure observed by confocal microscopy could not explain the changes in mechanical or sensory textures. The differentiating sensory attributes among treatments were adhesiveness, cohesiveness of mass, tackiness, firmness, fracturability, and deformability. Most notably, adding casein increased cohesiveness while maintaining water holding properties. Sensory texture properties could be explained by a combination of macroscopic structural changes (appearance), fracture properties, and postfracture breakdown pattern. Overall, it was demonstrated that casein can be used to alter whey protein gel structure such that sensory firmness and fracturability are decreased and cohesiveness is increased, while preventing a large increase in moisture release. PRACTICAL APPLICATION: There is a current desire to use alternative sources of protein in a variety of food applications, which requires the ability to design food structures with specific textural properties. Whey protein gels were used as a model soft solid structure with textural attributes of low cohesiveness and water release, and high firmness and fracturability. It was shown that adding casein modified the structure such that cohesiveness increased, firmness and fracturability decreased, and water holding ability was maintained. Using a second source of protein to modify a primary protein network appears to be a viable way to adjust textural properties.