EFFECT OF FAT CRYSTALLINITY ON LARGE DEFORMATION RHEOLOGY OF EMULSION-FILLED GELS

Laura Oliver ^1,2 Elke Scholten ^1,3 George A. van Aken ^1,2

¹Food Structuring team, Top Institute Food and Nutrition, Wageningen
²Flavour and Texture, NIZO Food Research, Ede
³Food Physics Group, Department of Agrotechnology and Food Sciences, Wageningen University, Wageningen

Several food products such as dairy products and processed meat can be described as gels filled with emulsions of semi-solid fat. An improvement of the health image of these products can be achieved by replacing the saturated semi-solid fat by unsaturated liquid oil. This replacement is challenging since solid fats play an important role in the rheological and structural properties of these food products. The aim of this work was to investigate the impact on the texture properties of emulsion-filled gels when saturated semi-solid fat is replaced by unsaturated liquid oil. For this study micellar casein, whey protein aggregate and gelatine were chosen as gel matrices and the fat firmness was varied by selection of the fat type (sunflower oil, poultry fat, pork fat, milk fat and beef fat) and variation of the temperature. As the emulsifier we used either sodium caseinate, whey protein aggregates or whey protein. Texture properties were investigated by uniaxial compression. The results show that the presence of emulsion droplets increases the gel rigidity for the studied systems as compared to the emulsion-free gel. An increase in solid fat content led to a moderate increase in gel stiffness for the whey protein aggregate gel, which was in good agreement with predictions according to the van der Poel theory for the effect of fat hardness on the rigidity of the filled gels. For the micellar casein and gelatine gels however, the magnitude by which the gel stiffness increased as a function of the solid fat content was much larger than expected on the basis of the van der Poel theory. Microscopical observation suggested that this was caused by an effective concentration of the fat droplets, either by droplet aggregation of an homogeneous gel matrix or by a restructuring of the droplets in the protein strands in an inhomogeneous protein matrix. These concentration effects appear to play a prominent role in the rigidity of the gels filled with semi-solid fat or rigid particles.

Dr. Laura Oliver Laura.Oliver-Hernandez@nizo.com