Protein foams

Partial etherification of the beech wood MGX with p-carboxybenzyl bromide in aqueous alkali yielded fully water-soluble xylan ethers with DS up to 0.25 without significant depolymerization the Mw determined by sedimentation velocity was 27 000 g/mol [400,401]. By combination of endo- 6-xylanase digestion and various ID- and 2D-NMR techniques, the distribution of the substituents was suggested to be blockwise rather than uniform. The derivatives exhibited remarkable emulsifying and protein foam-stabilizing activi-... 

When there is a high percentage of proteins, such as in gelatin—which will form an elastic film in conjunction with corn sirup and other sugar products—stability is not too much of a problem. In freshly whipped egg or vegetable protein foams, frappes, or mazettas, in which the foam product is incorporated as part of a complete food batch, the foam is assimilated before its stability becomes a factor and further processing tends to stabilize the foam. 

The foam drainage, surface viscosity, and bubble size distributions have been reported for different systems consisting of detergents and proteins. Foam drainage was investigated by using an incident light interference microscope technique. 

On considering the foaming capacity of these systems, we have found a synergistic effect for complexes of sodium caseinate with phosphatidylcholine, i. e., a four-fold increase in the half-life the foam as compared to the pure protein foam in the range of experimental conditions studied (pH 5.5-7.0 ionic strength 0.001-0.01 M). We note also here that pure phosphatidylcholine did not give fine stable foams at all under these same experimental conditions. Thus, it is evident that food-grade sodium caseinate nanoparticles can potentially possess dual functionality in food... 

In support of the possibility to manipulate foam stability by changing the nature of protein assembly in the presence of surfactant, Table 6.3 shows a correlation between molecular parameters of protein-phospholipid complexes and the visual appearance of foams stabilized by them in solutions of different pH. The data indicate that the foams stabilized by complexes of phospholipid liposomes with sodium caseinate exhibit a dramatic increase in stability as compared to the corresponding pure protein foams. (The phospholipid sample by itself did not make fine stable foams at any of the concentrations investigated). 

Table 7.3 Relationship between molecular parameters (A2, p) of sodium caseinate (0.5 wt%) + dextran sulfate complexes at pH = 6.0 formed in the bulk and at the interface of a protein foam, and the corresponding properties (J43, Q of the bilayer and mixed emulsions (20 vol% oil, 0.5 wt% sodium caseinate) containing 0.1 or 1.0 wt% dextran sulfate (Jourdain et aL, 2008 Semenova et al., 2009).

Many methods have been used to produce and characterize protein foams. The foaming characteristics of proteins are markedly influenced by conditions of preparation, measurement, and so forth (13-18). Because of the variety of methods employed, it is difficult to compare data from different sources. 

Tanner GJ, Moate PJ, Davis LEI, Laby RH, Yuguang L, Larkin PJ. 1995. Proantho-cyanidins (condensed tannin) destabilize plant protein foams in a dose dependent manner. Aust J Agric Res 46 1101-1109. 

K. Kalischewski, W. Bumbullis and K. Schugerl, Foam behavior of biological media, I, Protein foams, Eur. J. Appl. Microbiol. Biotechnol. 7(1979)21-31. 

K. Kalischewski and K. Schugerl, Investigation of protein foams obtained by bubbling, Colloid Polym. Sci. 257 (1979) 1099-1110. 

A number of factors contribute to the effectiveness of foam as a vapor-suppressant. These include the type of foam, its expansion ratio, its drainage time, the rate of application of the foam (gal per min/ft2), and its application density (gal/ft2). Chemical foams have become obsolete, with mechanical foams now being used worldwide. A mechanical foam that has recognized attributes for vapor suppression is aqueous film-forming foam (AFFF). It is a synthetic foam (as compared to protein foams) with a surfactant that is part fluorochemical and part hydrocarbon. It suppresses vapors by forming an aqueous film produced by draining its foam bubbles. 

The foaming capacity of succinylated soy protein was significantly better than those of the unmodifided proteins. Foam volumes progressively increased with pH from 3 to 10 (12). Succi-nylation caused a small increase in foaming capacity of cottonseed flour (38). Solubility is required for the production of protein foams (48), and succinylation substantially increased the foaming ability of soy isolate by enhancing their solubility. 

Pectins, produced from fruit wastes are valuable foaming agents for food industry that can substitute various protein and non-protein foaming agents (egg protein, butyric acid ethers, cellulose derivatives, lecithin, glycosides, etc.). 

Figure 12. A protein foam, showing unfolded protein molecules at the air-water interface.

Barker, D.K., Wilde, P.J., and Clark, D.C. Enhancement of protein foam stability by formation of wheat arabinoxylan-protein crosslinks. Cereal Chem., 493, 1998. 

The properties of proteins that promote emulsion formation are also important in the creation of foams. Poole and Fry [44] suggested that the ideal protein for foaming would posses high surface hydro-phobicity, high solubility, and a low net charge at the pH of the food product. To exhibit functional performance, the protein must reach the air/water interface. Rapid diffusion and unfolding at the interface is required to lower the interfacial tension between the air and the water phase [45]. Factors that increase the rate of protein diffusion have also been reported to enhance protein foaming [46,16]. 

Because protein-ba sed foams depend upon the intrinsic molecular properties (extent and nature of protein-protein interactions) of the protein, foaming properties (formation and stabilization) can vary immensely between different proteins. The intrinsic properties of the protein together with extrinsic factors (temperature, pH, salts, and viscosity of the continuous phase) determine the physical stability of the film. Films with enhanced mechanical strength (greater protein-protein interactions), and better rheological and viscoelastic properties (flexible residual tertiary structure) are more stable (12,15), and this is reflected in more stable foams/emulsions (14,33). Such films have better viscoelastic properties (dilatational modulus) ( ) and can adapt to physical perturbations without rupture. This is illustrated by -lactoglobulin which forms strong viscous films while casein films show limited viscosity due to diminished protein-protein (electrostatic) interactions and lack of bulky structure (steric effects) which apparently improves interactions at the interface (7,13 19). 

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