Hans Tromp

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My interest is in applying fundamental colloid chemistry to food systems. I do this in commercial projects and as a part time associate professor at the University of Utrecht.

Food systems are complex and usually not in thermodynamic equilibrium. They change in time with a broad range of characteristic time scales. Moreover, they often contain a broad range of structures, from molecular in size to visible. Different time scales and distance scales pose an interesting challenge to systematic science. However, it is often surprising how well the physical behaviour of food systems can be described by relatively simple models.

The focus of my scientific work is on interfaces in food systems. These interfaces can be between air and the food, but also inside the food between oil and water, or different watery regions. 

The commercial work is usually confidential. The open research I do is spread over three areas:

1. Dense protein systems
2. Water-water interfaces
3. Structure formation under shear

The project on dense protein systems is carried out within BRM, a collaboration between TIFN, DPI and the Universities of Eindhoven and Cambridge. It tries to describe and understand what is the state of protein molecules that are partly hydrated. This is important for improving the mouthfeel of high protein food, and the dissolution of protein-rich powders.

Water-water interfaces are found inside food systems between protein-rich and polysaccharide-rich regions. Often these regions are microscopic in size and dispersed. Water-water interfaces have properties similar to those of dialysis tubing (permeable for water and salt, but not for polymers). Understanding the structure, behaviour and how to manipulate this behaviour is important for manufacturing low-calorie products, basically made of 'structured water'. The project is carried out in the Colloids Chemistry group at the university of Utrecht and funded by an ECHO grant (NWO Chemische Wetenschappen) .

The project structure formation under shear is carried out by a master student from Colloid Chemistry of the University of Utrecht. It makes use of special equipment present at NIZO, by which food products can be sheared and observed by microscope at the same time. The observation are combined with measurements using stress and shear controlled rheometry. 

Movie 1. A phase separated mixture of aqueous solutions of pullulan and fish gelatine under a shear rate of 4.5/s, and the restoration of the structure after stopping the shear. Field of view 450 micron. The gelatine-rich phase was stained with rhodamine.

Movie 2. Custard under a shear rate of 1.5/s. Field of view 450 micron. The swollen starch granules are green, and particles of aggregated protein are red. Fat globules are visible as small black spheres. Note the different velocities of starch granules and fat globules suggesting different responses to shear stress of the weak network of starch granules and the serum in between. From observations like this NIZO tries to understand the role of serum viscosity in the creaminess of soft food products. 

Movie 3. A suspension of native tapioca starch granules in a whey protein solution. Field of view 450 micron. Shear rate 1.5/s. Note the usual rotational movement of the granules in a velocity gradient (which is perpendicular to the screen). This movement is made irregular by hydrodynamic interactions among the granules, and by transient clustering.