Foamability, protein-stabilized foam

In protein-stabihzed foams, protein flexibility is critical to the molecule functionality in stabilizing interfaces (Hailing 1981 Lemeste et al. 1990). This has important consequences in the development and stability of dairy foams and emulsions, where the heat treatment received by the material can define its foamability and dispersion properties. A symbiotic effect between native and denatured proteins on the emulsifying properties of whey proteins isolate blends has been observed by (Britten et al. 

Nemeth et al. [132] also report the effect of polyethoxy-polypropoxy block copolymers (EO .PO .EO , where m = 33 and 2.5 foam behavior of a protein—bovine serum albumin (BSA). These block copolymers reduced both the foamability and stability of the foam of BSA solutions at temperatures below the relevant cloud point where the solution was homogeneous. Filtration of the mixed solutions at the tanperature of these foam experiments produced essentially no enhanconent of foamability or foam stability. However, the filtration was done before foam generation so that the possibility of the decomposition of any putative metastable state during foam generation was not examined. Unlike with the PDMS-EOPO copolymer/Triton X-100 system, the possibility that antifoam effects at temperatnres above a measured cloud point for this EO-PO-EO -i- BSA system, which could be eliminated by removal of the relevant conjugate phase, was not explored. 

Table 10.3 shows the half-lifetime of the foam formed by solutions P-casein as a function of bulk concentration. The foamability of P-casein is very dependant on the bulk concentration of protein. Stable foams of P-casein were only found above a concentration of protein of 0.05 g/L. Then, the stability of the foam increased very steeply with the bulk concentration having a much larger halflifetime for the foam formed with 0.1 g/L P-casein. 

A foam is a dispersion of a gas in a liquid or a solid. The formation of foam relies on the surface activity of the surfactants, polymers, proteins, and colloidal particles to stabilize the interface. Thus, the foamability increases with increasing surfactant concentration up to critical micelle concentration because above critical micelle concentration, the unimer concentration in the bulk r ains nearly constant. The structure and molecular architecture of the foam is known to influence foam-ability and its stability. The packing properties at the interface are not excellent for very hydrophilic or very hydrophobic drug. The surfactant promoting a small spontaneous curvature at interface is ideal for foams. Nonionic surfactants are the most commonly used one. The main advantage with foams is its site-specific delivery and multiple dosing of the drug. ... 

Measurements showed that foamability and foam stability are mutually independent—wines may produce a lot of foam but it is not necessarily very stable. A close correlation has been observed between foamability and protein content. A decrease in protein content of a few mg/1 can lead to a 50% drop in foamability (Malvy et al., 1994). However, Maujean et al. (1990) did not find any simple correlation between protein content and foam stability. 

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