Foaming capacity

Alcohol sulfates are excellent foaming surfactants. According to the Kitchener and Cooper classification [148], alcohol sulfates form metastable foams. However, quantitative values cannot easily be compared because foam largely depends not only on the instrument used to produce and evaluate foam but also on the concentration of surfactant, impurities, temperature, and many other factors. In addition, a complete characterization of the foam capacity should take into account the initial amount of foam, its stability, and its texture. 

FIG. 15 Foaming capacity of alcohol sulfates and alcohol ether sulfates at 0.28 g/L active matter at 20°C, DIN 53902. (From data in Ref. 149.)... 

Maurer et al. [57] determined the foaming power of octadecyl sulfuric acid and several of its salts, such as sodium, triethylamine, triethanolamine, and some amino acids. Foam capacity, measured by the Ross-Miles test [150] at 60°C, was in the range of 180-210 mm showing comparatively few differences. 

The foaming capacity of milk is related to the ability to form stable air bubbles. One factor that can stabilize air bubbles is the presence of a film coating on... 

Another important group of anionic surfactants are AESs, which are used in laundry and cleaning detergents as well as in cosmetic products. Characteristic properties of AESs are the ability to function in hard water, high foam capacity and low irritation to skin [16]. 

A study of the foaming capacities and stabilities [10] of a variety of air-entraining agents in a solution of cement extracts showed that commonly used anionic air-entraining agents, such as sodium dodecyl sulfate and sodium resinate (1) were visually precipitated from solution, (2) retained their ability to form stable foams after precipitation with only minor amounts of admixture left in solution, and (3) lost the major part of their ability to form stable foams after filtration. It was further shown from studies in cement pastes firstly that the admixture should be adsorbed on the solid particles of the paste with the non-polar ends of the molecule pointed towards the water phase, imparting a hydrophobic character to the cement... 

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... 

Rapid shaking of a horizontal graduated cylinder containing a protein solution produces a foam that can be measured by its volume (2 16). Foaming capacity of sparged foams is measured by the ratio of the volume of gas in foam to the volume of gas sparged, or by the maximum volume of foam divided by the gas flow rate ], 10, 20, 21). 

For the studies presented in this chapter, samples of peanut and cottonseed meal suspensions were evaluated for foam capacity, stability, and viscosity measurements as described by Cherry and coworkers (23, 24, 22). Vegetable protein suspensions at the appropriate concentration and pH were whipped in a Waring-type blender. After blending, the whipped products were transferred to a graduated cyclinder. Milliliters of foam were recorded immediately and at various time intervals to determine capacity and stability. A Brookfield viscometer and... 

Foam capacity and stability were increased by increasing... 

Empirical multiple linear regression models were developed to describe the foam capacity and stability data of Figures 2 and 4 as a function of pH and suspension concentration (Tables III and IV). These statistical analyses and foaming procedures were modeled after data published earlier (23, 24, 29, 30, 31). The multiple values of 0.9601 and 0.9563 for foam capacity and stability, respectively, were very high, indicating that approximately 96% of the variability contributing to both of these functional properties of foam was accounted for by the seven variables used in the equation. 

Multiple linear regression equations were also developed for foam capacity and stability based on pH and the data on composition of soluble and insoluble fractions in the suspensions sumarized in Figures 2 and 4 (Tables V and VI). 

Multiple r2 values of 0.9346 and 0.9280 were obtained for these equations of capacity and stability, respectively. The relative importance of each respective partial regression coefficient was determined by comparison of B values (32). These evaluations indicate that the most important variables in the two models for foam capacity and stability are soluble protein, soluble and insoluble carbohydrate and ash, and insoluble fiber. 

The experimental data in Figures 2 and 4 were used in multiple regression equations to predict foam capacity and stability of 2% to 30% suspensions adjusted to pH values of 1.5 to 11.5 (Figures 6 and 7). Observed and predicted data of the... 

Table III. Empirical multiple linear regression model describing foaming capacity as a function of pH and suspension concentration.

Table V. Multiple linear regression analysis of foam capacity...

Figure 6. Experimentally observed and mathematically simulated regression lines of foam capacity of different percentages of glandless cottonseed flour in suspensions at various pH values. Experimental 4%, 10%, and 16% suspensions were run at pH 3.5, 6.5, and 9.5 to test the reliability of the multiple linear regression analysis. Quantitative data used in this analysis are in Figures 2 and 4.

Foam properties related to salt. The addition of sodium chloride to soybean protein suspensions caused them to form high-capacity, low-stability foams (13). It was suggested that foam capacity increased because salt improved protein solubility at the interface of the colloidal suspension during foam formation, but retarded the partial denaturation of the surface polypeptides of proteins that are necessary for protein-protein interaction and stability. 

The smallest increases in foam capacity occurred at pH 6.7. Percentages of protein in the soluble fractions varied at this pH. Foam capacity and stability improved and decreased, respectively, at this pH as the salt content of the suspension was increased. The two-step pH adjustment (23) of 6.7 to 4.0 to... 

Figure 14. Foam capacity and protein solubility properties of defatted soybean, peanut, field pea, and pecan seed flour suspensions at various pH values (4T)...

Foam properties related to seed type. Soybean flour suspensions produced thick egg white-type foams at all pH levels tested except at 4.0 (Figure 14 47). Although the increase in capacity of suspensions at pH values 6.5 and 4.0 was identical, a medium thick foam was produced by the latter. At pH 4.0, the level of soluble protein in the suspension was significantly lower than at the higher pH values the latter three percentages of protein were similar. A decline in foaming capacity at pH... 

Foam capacity of peanut seed flour suspension at pH 4.0,... 

Suspensions of field pea flour at pH 6.7 and 8.2 (including the two-step adjustment) contained similar high quantities of soluble protein at pH 4.0, most of the protein was Insoluble. Foam capacity of suspensions was higher at pH 8.2 than at 4.0 and 6.7. The two-step pH adjustment did not improve foam capacity over that of the one-step change as shown with the soybean and peanut products. The foam produced at pH 4.0 was thinner than those at pH 6.4 and 8.2 the latter three products had similar consistencies. 

Thus, differences in functionality of these two suspensions cannot be related to protein quality as distinguished by the gel electrophoretic techniques used in this study. However, these data suggest that solubility of the major storage proteins, or their subunit components, contribute to foam capacity. In addition, other seed constituents, such as carbohydrate and ash (for example, field pea and pecan, respectively) may be equally involved (especially when the suspension pH is 1.5). 

Foaming Capacity and Stability. Pepsin digestion of soy protein has been proposed as a method for making a whipping protein for egg albumen replacement (42, 45) and for extenders for albumen in bakery and confectionery formulations (46). Puski... 

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