George van Aken

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/files/854What I like about working at NIZO is that it allows me both to be involved in basic food science and to translate this science into practical applications. 

This combination fits me as a person: I'm always curious about how Nature works, how mechanisms act together producing the complexity in real life. But I find it even more exciting to make this knowledge work to solve problems and create new possibilities.

I started by studying surfactant behavior in my PhD study. How do surfactants lower the interfacial tension, assemble into micelles and liquid crystalline and microemulsion structures? How do they lower the interfacial tension between oil and water and how to they protect emulsion droplets against coalescence?

geneealized phase diagramme for surfactants and polar lipids

At NIZO I used proteins and peptides to stabilize emulsions and foams. Which properties are needed for a peptide to stabilize an emulsion? In food systems, usually proteins are used in combination with polar lipids and surfactants to stabilize emulsions and foams. These components can interact in solution and in the adsorbed layer, whichih strongly modifies their behaviour.

And what is a food emulsion without the fat? So I studied fat crystallization behaviour and how this can be used to control cream and butter properties. Fractionation and texture of butterfat was related to the composition and crystallization rate of the various triglyceride fractions in milkfat. Plastic solid fat can be produced by adapting the cooling rate and time of kneading of the crystallizing fat to the cristallization properties, producing a structure of globules of crystallized fat which are sintered together.

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The stability of food emulsions and foams was still obsure, and required more fundamental research, which I did in a collaboration with TI food and nutrition. Teaming up with Franklin Zoet and PhD students Natalie Hotrum and Theo Blijdenstein, we clarified the mechanisms of coalescence in protein stabilized emulsions, of polysaccharides in the stabilizing and thickening of emulsions and the whipping behaviour in recombined creams. 

Proteins appeared to form vary stable thin films between the emulsion droplets, that very effectively inhibit coalescence up to very high volume fractions (> 90%), but are very brittle and rupture due to external forces.

Polysaccharides can thicken an emulsion, but at the same time can destabilize the emulsion by inducing droplet aggregation, by depletion and bridging mechanisms.

Emulsions of partailly crystalline fat can entrap and stabilize air bubbles and later form stiff strctures by partial coalescence. This process was shown to be regulated by the spreading behaviour of the oil at the bubble interface, which can be controlled by using the appropriate surfactants. 

But food is to be consumed. The proofing of the cake is in the tasting. The next step was therefore to investigate the role of emulsion droplets in mouthfeel of foods. I led a project at TIFN in which we identified specific roles on mouthfeel perception of emulsion droplets in the interaction with saliva, the interaction with the tongue surface and the interaction with a thickened or gelled matrix. A recent step was to identify the interaction with the mechanoreceptor nerve endings in the papillae, quantify their role in perception. This work has given a lot of new understanding of sensory attributes such as thick, creamy, gritty and astringent, and currently gives direction to projects for NIZO clients.

As a counterside to the highly appreciated "creamy" mouthfeel produced by emulsified fat, unfortunately fat is also the most energy dense of the main nutrients. How can the fat content be reduced, still keeping the sensory quality of a product? How can can fat be formulated in such a way that it is more satiating and overall energy intake is reduced? These are the  issues that I have worked on by in-vitro studies of gastro-intestinal processing of food emulsions and in- vivo studies in collaboration with Masstricht University and IFR. 


Some promissing results have been found in these studies, which I now try to interpret and generalize by mechanistic in-silico modelling of the physiological responses know from physiological literature to emulsion digestion as establised in-vitro. Indeed, by modelling a number of well know physiological responses, such as teh regulation of stomach emptying time, small-intestinal transit time and hormonal responses, a fairly good prediction can be obtained for experimental VAS scores of hunger and fullness and hormone blood levels for the experimental model systems studies by us.




More information about me can be found on LinkedIn

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