Rheological and Microstructural Measurements on Gels at Initial State of Fracture 9 CAMILLA OLSSON, MAUD LANGTON, MATS STADING and ANNE-MARIE HERMANSSON Structuring in Plant Materials: From Molecules

Texture is an important property for most food products and is usually characterised by different rheological methods together with data from microstructural investigations. However, the correlation between results from rheological measurements and microstructural data is not always unambiguous. Therefore the demand of developing new types of rheological measurements as well as structural measurements has arisen. We will in this study show some examples of different methods describing the initial state of fracture of particulate protein gels. The rheological measurements are attempts to characterise the behaviour of gel structures during gradual break down. Within rheology the texture is studied by dynamic measurements. To obtain equivalent information from microstructural data, we have in this study monitored the microstructure of the gels during successive deformation under a confocal laser scanning microscope (CLSM). As model system we have used particulate β-lactoglobulin gels with microstructures that differed in density, size of pores and clusters, thickness of strands and connectivity of strands. The medium in which the β-lactoglobulin gel has been formed was varied; water, amylopectin solution and gelatin. (The gelatin gelled after the β-lactoglobulin network was formed.) The rheological measurements were performed by using a Stress Tech rheometer. A constant increasing shear stress was applied until the gel broke, at the same time as the shear rate and the shear strain were measured. We observed that the shear rate varied dependent on gel type. At an initial state of the measurements the shear rate showed a maximum for some of the gels, see Figure 1. Figure 1. Shear rate versus shear stress at a constant stress rate for a mixed gel of 8% βlactoglobulin/5% gelatin. 4 3 2 1 0 3 0