Molecular control of foam properties
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Abstract
Protein-stabilized liquid foams are fascinating multiscale systems: the structural properties of a protein define its interfacial activity and interactions with other molecules. Its assembly at air-water interfaces together with drainage determine lamella stability. Coalescence and coarsening promote bubble growth affecting macroscopic foam stability represented by the foam height decay.
This dissertation deepens the understanding of which structural properties of a protein promote increased foam stability. A method for monitoring the temporal evolution of the mean bubble size and circularity with common lab equipment and open-source software was developed. Comparing foams stabilized by hydrophobin and BSA, two proteins with fundamentally different properties, showed that large hydrophobic patches at the protein surface promote a higher foam stability. Adding polysaccharides to BSA-stabilized foams revealed that an increased solution viscosity enhances foam stability, but the stiffness and charge of the polysaccharide need to be considered. Modifying the tertiary structure of BSA by varying the solution pH revealed that uncharged proteins promote a more resilient interfacial arrangement facilitating an increased stability of dry foams. A high protein charge increases solution viscosity, thereby retarding drainage and improving the stability of wet foams. Investigating an oat drink showed that conformational changes provoked by heat and enzymatic treatment of oat proteins reduce foam stability.