Food as soft matter

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A fantastic article about the soft matter aspects of food was recently written by Raffaele Mezzenga and his swiss colleagues in Nature Materials. The figure below concisely summarizes how many phenomena in the food sciences are the result of colloid interactions, with the example of casein proteins. These proteins can be treated as hard spheres or as the structural elements of a continuous network, depending on the interparticle interactions between them:

FoodDiagram.jpg

The top central figure shows the interaction energy (U/kT) as a function of volume fraction. At low volume fractions, but strong interactions between particles, fractal networks form. In the opposite case of high volume fractions with low interaction energies, dense suspensions are created. Three specific cases are illustrated around the central figure: A. Casein micelles in solution can be treated as hard spheres. The viscosity of the suspension increases until the system reaches a fully jammed state. The photo shows how the mixture can be turned upside down without separating. B. When a polysaccharide polymer is added to the system, various phases are possible through spinodal decomposition. Depending on the relative concentration, the system can form: (1) Xantham-rich droplets, (2) casein-rich droplets, or (3) a bicontinuous phase. C, D. The figures at the top show the similarities between ceramic materials (C) and casein networks in yogurt (D).


Homogenization

You know how it says homogenized on every container of milk and as a kid you never knew what it was. It essentially changes the size of solids (colloidal particles) of fat and proteins in solution. By decreasing the size of the particles it creates a more stable dispersion.