Aggregative foam stability

The aggregative foam stability is manifested in changes of the foam dispersity. There are two main causes of aggregative foam stability disturbances a) coalescence of foam cells due to the rupture of bilateral films separating them b) disappearance of foam cells due to gas penetration from small cells into larger ones (Ostwald ripening). 

Experimental values of aggregative foam stability characteristics are presented in Table 6.1. The rate constants of rapid and slow coalescence can be assigned, in accordance with the above considerations, to hydrostatically non-equilibrium and equilibrium conditions, respectively. Table 6.1 Aggregative foam stability characteristics... 

The study of aggregative foam stability has shown that the change of the mean equivalent radius in the foam volume is... 

Proteins of egg white denature more rapidly than those of whey protein concentrate (13, 34). However, isolated p-lactoglobulin from the whey concentrate was more susceptible to surface denaturation than egg white ovalbumin. These data suggest that whey contains substances that protect the proteins from surface denaturation and may account for the lower stability of whey protein concentrate foams than those of egg white protein. A balance between the disaggregation effect of select pH values and the tendency toward greater aggregation of proteins at higher heating temperatures were correlated closely with maximum foam stability (13, 15). 

Foaming capability relates to both foam formation and foam persistence. Surface tension lowering is necessary, but not sufficient. Other important factors include surface elasticity, surface viscosity and disjoining pressure [60]. Considering stability to aggregation, film thinning and bubble coalescence, the factors favouring foam stability can be summarized as follows ... 

The second example deals with fluid interfaces in protein foams. Protein foams are most relevant in food science and engineering, e.g., in the form of mfik foams on a cappuccino. A foam is an aggregate of stabilized gas bubbles. These gas bubbles in turn are stabUized by adsorbed proteins and surfactants at the hquid—gas interface. In the example illustrated in Fig. 14, we present data for P-lactoglobifiin (BLG) which have been obtained from SFG, eUipsometry, and surface rheology. 

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