EFFECT OF EMULSION DROPLETS ON THE RHEOLOGY OF WHEY-PROTEIN ISOLATE GELS

Rhe effects of droplet size and emulsifier type on the rheology of whe y protein isolate (WPI) gels containing emulsion droplets was studied. Gels were prepared by dispersing droplets of com oil (20 wt%, d32 = 0 .7 - 4 mum) in a 10 wt% WPI solution (pH 7.0, 50 mM NaCl), and heating at 90C for 15 min. Gel strength was determined by measuring the stres s of gels at 20% compression using an Instron Universal Testing Machin e. Droplets stabilized by WPI increased the gel strength, those stabil ized by non-ionic surfactants (Tween 20 and Triton X-100) decreased it slightly, and those stabilized by SDS decreased it drastically. Gel s trength increased as the droplet size decreased for droplets stabilize d by WPI, but was relatively insensitive to the size of droplets stabi lized by the small molecule surfactants. These observations may be exp lained in terms of the interactions between the emulsifiers and the pr otein network. Droplets coated with emulsifiers which can be incorpora ted into the protein network reinforce the structure and so increase g el strength, whereas droplets coated with emulsifiers which cannot be incorporated into the protein network disrupt the three dimensional st ructure of the gel and decrease its strength.