Whole casein foam film thickness

Regarding the systems used in this study, we use the same proteins as in the previous section (whole casein and P -casein) and they are mixed with Tween 20, respectively. This is a low molecular weight surfactant used in the food industry, which is water soluble and nonionic. The different behavior of these two mixed systems is again discussed on the basis of fundamental magnitudes such as surface tension and foam film thickness. 

Contrary to the case of P-casein/Tween 20 systans, although the surface pressure isotherms shed some light on the surface structure of whole casein/Tween 20 systems, the information extracted does not provide a full explanation to the behavior of foams stabilized by this system. Taking into account the key information provided by the confinement in thin liquid films as regards the foam stability of whole casein and P-casein solutions, which was examined in the previous section, let us evaluate the properties of the foam films stabilized with whole casein/Tween 20 mixtures. Table 10.2 shows the thickness of foam films stabilized by pure whole casein, pure Tween 20 and two mixed systems under similar conditions to the foam stability, and the surface pressure experiments. The film thickness is measured by using Scheludko s microinterferometric method (Maldonado-Valderrama and Langevin, 2008). 

Regarding the drainage of a foam film stabilized by sole whole casein, this has been discussed in the previous section. The thickness of the whole casein film diminishes in a continuous manner until reaching a finite final thickness that corresponds to a bilayer of caseins with somehow screened electrostatic repulsion between layers and a higher intermolecular interaction between the different monomers composing the whole casein (Maldonado-Valderrama and Langevin, 2008). 

Thickness of the Foam Films Formed by the Pure and Mixed Solutions of Whole Casein and Tween 20... 

Firstly, the stability of the foam formed by P-casein and whole casein appears very different, the former being more stable. In order to further investigate this issne, we evalnate several surface properties of these two proteins. The surface tension and surface rheology do not seem to be accurate enough to account for this large difference in foam stability, since they show very similar values. However, the thickness of the foam films stabilized by the two proteins respectively seems to determine the ultimate behavior of the foam. Hence, the thicker foam film measured for P-casein probably prevents coalesce of air bubbles resulting in more stable foam formed by this protein as compared to whole casein. 

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