Lipid protein foam, stability

Biliaderis, 1989 Oomah and Mazza, 1998b). Flaxseed gum exhibited good foam stability at a level of 1% and maximum viscosity at pH 6.0-8.0 (Mazza and Biliaderis, 1989). Oomah and Mazza (1998b) reported that lipid removal significantly increased apparent viscosity values of flaxseed gum. Furthermore, viscosity of seed, cake, and flake samples was significantly related to protein (r = 0.97) and carbohydrate (r = 0.91) fractions, which were related to mucilage fraction of the seed. 

Foams stabilized with proteins, such as egg white, can be quite sensitive to the presence of oil (fat) droplets (see also Section 5.6.7). Just as is the case with foam sensitivity to oil in other industries, the presence of even small amounts of oil (0.03 mass % in foods [814]) can destabilize a foam. Oils such as lipids are thought to interfere with foaming by displacing proteins from the air-aqueous interface. One approach to improving the foam stability involves combining acidic proteins, such as whey or serum albumin, with basic proteins [814]. 

As a rule, the fluid dispersions (emulsions, foams) are stabilized by adsorption layers of amphiphile molecules. These can be ionic and nonionic surfactants, lipids, proteins, etc. All have the property to lower the value of the surface (or interfacial) tension, o, in accordance with the Gibbs adsorption... 

Although whey protein concentrates possess excellent nutritional and organoleptic properties, they often exhibit only partial solubility and do not function as well as the caseinates for stabilizing aqueous foams and emulsions (19). A number of compositional and processing factors are involved which alter the ability of whey protein concentrates to function in such food formulations. These include pH, redox potential, Ca concentration, heat denaturation, enzymatic modification, residual polyphosphate or other polyvalent ion precipitating agents, residual milk lipids/phospholipids and chemical emulsifiers (22). 

The results on formation and stability of black foam films, on the first place those on bilayer foam films (NBF) (see Sections 3.4.1.2 and 3.4.4) have promoted the development of methods which enable lung maturity evaluation. The research on stability of amphiphile bilayers and probability for their observation in the grey foam films laid the grounds of the method for assessment of foetal lung maturity created by Exerowa et al. [20,24]. Cordova et al. [25] named it Exerowa Black Film Method. It involves formation of films from amniotic fluid to which 47% ethanol and 7-10 2 mol dm 3 NaCl are added [20,24]. In the presence of alcohol the surface tension of the solution is 29 mN m 1 and the adsorption of proteins from the amniotic fluid at the solution/air interface is suppressed, while that of phospholipids predominates. On introducing alcohol, the CMC increases [26], so that the phospholipids are present also as monomers in the solution. The electrolyte reduces the electrostatic disjoining pressure thus providing formation of black foam lipid films (see Sections 3.4.1.2 and 3.4.4). 

Preparation of food foams and emulsions requires the creation and stabilization of air-water or oil-water interfaces. Interfaces foimd in food systems contain a range of surface-active molecules and the interactions between these components determine the long-term stability of the foam or emulsion. The most common species present at the interface will be proteins and various small, highly mobile molecules such as surfactants or lipids. Both proteins and surfactants (or lipids) are capable, on their own, of stabilizing interfaces, but they do so by different molecular mechanisms (Wilde et al., 2004). 

The interfacial rheology of protein adsorption layers has been intensively studied in relation to the properties of foams and emulsions stabilized by proteins and their mixtures with lipids or surfactants. Detailed information on the investigated systems, experimental techniques, and theoretical models can be found in Refs. [762-769]. The shear rheology of the adsorption layers of many proteins follows the viscoelastic thixotropic model [770-772], in which the surface shear elasticity and viscosity depend on the surface shear rate. The surface rheology of saponin adsorption layers has been investigated in Ref. [773]. 

Foams of PIN-a and, to a smaller extent, of PIN-b are stabilized especially in the presence of polar wheat lipids. In this respect, PIN-a is clearly superior to egg white proteins as shown by the following comparison. After a drip off time of 5 min, a foam density of 0.028 was obtained with 0.3 mg of PIN-a/ml, while 1.25 mg/ml of egg white proteins were required for this purpose. 

Surfactant molecules can be diverse in structure, and there are many examples of surfactants in everyday life, from the soaps we use to wash with, to the lipids that make up our cell membranes, and even to the proteins that help to stabilize the foam on your beer. ... 

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