FOOD HYDROCOLLOIDS Food Hydrocolloids 22 (2008) 1574–1583 Quantification of a 3D structural evolution of food composites under large deformations using microrheology Ladislava van den Berg a,b,Ã , H. Jan Klok a,c , Ton van Vliet a,d , Erik van der Linden d , Martinus A.J.S. van Boekel b , Fred van de Velde a,c a TI Food and Nutrition (formally known as Wageningen Centre for Food Sciences), P.O. Box 557, 6700 AN Wageningen, The Netherlands b Wageningen University and Research Centre, Product Design and Quality Management Group, Bomenweg 2, 6703 HD Wageningen, The Netherlands c Texture Department, NIZO Food Research, Kernhemseweg 2, P.O. Box 20, 6710 BA Ede, The Netherlands d Wageningen University and Research Centre, Food Physics Group, Bomenweg 2, 6703 HD Wageningen, The Netherlands Received 26 July 2007; accepted 2 November 2007 Abstract Microrheology involves simultaneous determination of microstructure and deformation properties, which is essential for understanding structure–deformation relationships. The unit used combines a confocal laser scanning microscope with a compression unit. The main advantage of this approach is that the changes in the microstructure during deformation can be visualised and quantified in three dimensions. It was used to measure microstructural changes and breakdown mechanisms in whey protein isolate/polysaccharide gels. Microstructural changes in protein continuous and bicontinuous gels were quantified. The changes relate to the amount of serum released from the gels during compression. Additionally, the gels showed similar breakdown mechanisms, i.e. they fractured through the protein beams into the serum phase. r 2007 Elsevier Ltd. All rights reserved. Keywords: Microrheology; Microstructure; Deformation; Dynamics; Mixed gels; Whey proteins; Polysaccharides; Composites 1. Introduction One of the important characteristics of semi-solid foods affecting their physical and sensorial properties is their microstructure, and in particular changes therein during deformation. These can be visualised and followed in a microrheology set-up. The set-up combines a confocal laser scanning microscope (CLSM) with a compression unit. Changes in the microstructure can be deduced from a series of microstructural images. These are measured simulta- neously with the large deformation properties of the product during its deformation, which provides useful insights in the structure–deformation relationship. More- over, combining this type of results with sensorial data can identify the relationships between physical and structural properties of foods and the sensation they produce during consumption. The physical and physico-chemical properties of semi- solid food products, as desserts, processed meats, confec- tionary, and so on, can be well approximated by mixed gelled systems. The most important constructional materi- als of these model systems are proteins and polysaccharides (Tolstoguzov, 1986). The combination of native or denatured proteins with neutral or anionic polysaccharides used in foods can give a great number of mixed gels with different structural and physical properties (Brownsey & Morris, 1988; de Jong & van de Velde, 2007; Tolstoguzov, 2000). One of the most widely used proteins in foods is whey protein (de Wit, 1998). Its gelation is usually achieved by heating (Aguilera, 1995; Mulvihill & Kinsella, 1987), high-pressure treatment (Ipsen, Otte, Dominguez, & Qvist, 2000), or by a cold gelation process (Alting, Hamer, de Kruif, & Visschers, 2003). The effects of polysaccharides on the aggregation and gel formation of a whey protein solution differ depending on the nature of the polysaccharide, ARTICLE IN PRESS www.elsevier.com/locate/foodhyd 0268-005X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2007.11.002 Ã Corresponding author at: Texture Department, NIZO Food Research, Kernhemseweg 2, P.O. Box 20, 6710 BA Ede, The Netherlands. Tel.: +31 318 659 580; fax: +31 318 650 400. E-mail address: Ladislava.van.den.berg@nizo.nl (L. van den Berg).