Effect of Protein on the Texture of Food Emulsions under Steady Flow W. Jang, A. Nikolov, and D. T. Wasan* Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, Illinois 60616 K. Chen and B. Campbell Kraft Food Inc., Glenview, Illinois 60025 The texture of food emulsions was quantified as the structure factor using the backlight scattering technique. The change of the texture of food emulsions under steady flow was monitored in terms of the structure factor. The role of different types of protein (sodium caseinate and soy protein) on the change of texture of food emulsions under steady flow was studied. The emulsion stabilized by sodium caseinate was more stable under steady flow than the food emulsion stabilized by FP940 (partially hydrolyzed soy protein). The layering of caseinate submicelles in the film between the fat particles was suggested as a reason for the greater stability of the sodium caseinate stabilized emulsion under steady flow. The FP940 stabilized emulsion showed a sudden change of texture at a shear rate of 200 rad/s (the threshold), while the sodium caseinate stabilized emulsion was relatively stable under this shear rate. The FP940 stabilized food emulsion with a high fat concentration had a more ordered texture, represented as a greater structure factor; however, this texture degraded quickly under steady flow. Versa Whip 500 (highly hydrolyzed soy protein) was compared with FP940 (partially hydrolyzed soy protein) for their effects on the stability of food emulsions under steady flow. The stability of a food emulsion under steady flow improved as the concentration of Versa Whip 500 (highly hydrolyzed soy protein) increased from 1 to 2.5 wt % in the aqueous phase. The Versa Whip 500 stabilized emulsion had soy protein micelle layering in the film between the fat particles, which helped to stabilize the fat particles under steady flow. 1. Introduction Many food products, such as salad dressing, marga- rine, soft drinks, and cream liqueurs, are emulsions. Food emulsions meet the needs of the consumer by having a low fat content, a high nutritional value, and a pleasant taste. Soy proteins are widely used as food ingredients. Their flavor, color, and high protein content are great advantages in their application to dairy products, especially when a high level of protein is required. 1,2 Soy proteins are now used to stabilize food emulsions, which were conventionally stabilized by sodium caseinate (a milk protein). Protein plays a role in stabilizing fat particles (crys- tallized oil droplets) inside food emulsions. Protein forms an adsorbed layer around the fat particles, stabilizing them. A new stabilization mechanism of fat particles by protein micelles was reported. 3 It was found that some protein (sodium caseinate) helps to stabilize a food emulsion through micelle layering (caseinate submi- celles) in the film between the fat particles. The texture of the fat particles inside the food emulsion (average particle size, particle-particle spacing, and particle ordering structure) is subjected to a change under steady flow encountered during processes such as transportation, pouring, and whipping. The texture of the fat particles needs to withstand the shear stress in order to meet product requirements. It is important to understand the role of proteins on the texture and the stability of food emulsions under steady flow. The texture of fat particles inside whipped cream by using transmission and scanning electron microscopy has been studied. 4-6 Qualitative information about the texture of the fat particles was reported. However there are few quantitative descriptions of the texture of fat particles due to the lack of measuring methods and the complexity of food emulsions. The backlight scattering technique based on the Kossel diffraction pattern has been used to quantify the texture of food emulsions in terms of the structure factor. 7 The structure factor can be transformed into the radial distribution function, which can provide the effective interaction potential of the particles in the presence of a many-body interaction. Xu et al. 7 applied the backlight scattering technique to elucidate the effects of fat particle-particle interactions on the tex- ture and stability of food emulsions. They found that, using a statistical mechanics approach, the theoretical calculations for the texture of the food emulsion (rep- resented as the structure factor) are consistent with the results from the backlight scattering technique for a bidisperse system consisting of fat particles and mi- celles. We investigated the role of different kinds of proteins (sodium caseinate and soy protein) on the texture of food emulsions under steady flow. The change of the fat particle texture inside the food emulsion under steady flow was monitored in terms of the structure factor using the backlight scattering technique. The effects of * To whom correspondence should be addressed. Tel.: (312) 567-3001. E-mail: wasan@iit.edu. 4855 Ind. Eng. Chem. Res. 2005, 44, 4855-4862 10.1021/ie049553z CCC: $30.25 © 2005 American Chemical Society Published on Web 10/28/2004