Foam stabilizers, defined

Foam stability in the presence of oil can be described from thermodynamics in terms of the spreading and entering coefficients S and E respectively. These coefficients are defined as follows ... 

Indicates additive discussed in this chapter. Other additives discussed in this chapter but not defined above are adjuvants, foam stabilizers and foaming agents. These are described in Table 11.2. For historical reasons Modified starch is an exceptional category, because all the other categories are functional uses, whereas modified starches are a group of substances. 

Regarding foam stability, it has been recognized that the surface tension under film deformation must always change in such a way as to resist the deforming forces. Thus, tension in the film where expansion takes place will increase, while it will decrease in the part where contraction takes place. A force exists that tends to restore the original condition, which is film elasticity, defined as... 

Functional properties, as considered from the point of view of the food processor, are those properties which impart desired physical characteristics to the products. For example, foam stability would be an important functional property to a producer of whipped toppings. From the perspective of the consumer, this functional property may contribute to satisfaction and lead to repeat purchases. Increasingly, however, the consumer is concerned with the nutritional impact of his purchases. Thus, the food industry will be pressured to expand its concept of functional properties to include nutritional considerations. Martinez (1) has recently suggested that functionality be defined as "the set of properties that contributes to the desired color, flavor, texture, and nutritive value of a product". In order to assess the nutritive value of a product, one must evaluate more than the presence of the nutrients one must evaluate nutrient bioavailability. 

Foam Stability Measurements. The average lifetime (LF) is a property of bulk foams that is useful in ranking foams in order of stability. LF is defined as the area under the drainage profile divided by the initial foam height The apparatus used to determine these drainage profiles is shown in Fig. 9. 

Food foams are usually made by bubbling, whipping, or shaking a protein-containing solution. Several measures of foaming capacity of proteins and other stabilizing agents exist, such as overrun, which quantifies the amount of foam produced, defined as ... 

The quantity xp is a much better defined characteristic of foam stability (since the pressure in the borders along the height of the foam column remains constant during its destruction). This parameter is also much more sensitive to the kind of surfactant, electrolyte concentration and other additives, compared to the lifetime of the foam in gravitational field, with an averaged pressure value from 0 to pgH. Estimation of the stability of foams from different surfactants by xp and by the Ross-Miles test has been reported in [16]. The results are discusses in Section 7.6.1. The advantages of the Foam Pressure Drop Technique and, respectively, xp as a characteristic of the foam stability, are clearly shown. 

The method for investigating foams at high pressure drop in Plateau borders permits the estimation of foam stability under strictly defined conditions (see Section 7.2). This method enables measurement of foam lifetime tp at a certain constant pressure as well as at reaching the critical state of the film. 

Foam Stability. A plastic cylinder (diameter 7 cm, height 9 cm) having a wire net with a mesh size of 1 mm x 1 mm is filled with foam and the amount of foam is found by weighing (A gram). The cylinder is then placed on a funnel on top of a glass cylinder of 100 ml. After 30 minutes the weight (B) of drained liquid in the glass cylinder is determined. The foam stability FS is defined by the equation ... 

Although the volume of foam was increased by limited proteolysis, the stabilities of the foams, defined as the time required for one half of the weight of the foam to drain from the foam as free liquid, were greatly decreased by this same limited proteolysis. Presumably the increased initial polypeptide concentration in the hydrolysates favors more air incorporation. However, the polypeptides apparently do not have the surface activity required to give a stable foam. The decrease in foam stability becomes evident in the first 30 min of the enzyme reaction. Further hydrolysis results in peptides which lack the ability to stabilize the air cells of the foam. Thus a limited hydrolysis may be advantageous for utilizing whey proteins in foams since the specific volumes of the foams were increased 25% by such treatment. The decrease in foam stability which results from limited hydrolysis can be compensated for by adding stabilizers such as carboxymethyl cellulose (19,27). 

It is also important to stress that the Bikermann test determines foam stability under dynamic conditions, and as the bubbles move up the eolumn to the interface under the buoyaney force (Arehimedes), they are also subjected to (Stokes) frietional forces. Therefore, the time to reaeh the surfaee ean be be defined by the following ... 

Aveyard et al. [162] illustrate the effect of hydrophobed spherical glass particles on foam stability by defining a half-life ratio T p as... 

As shown in Figure 10.3 for the natural gas-crude oil system, this study revealed a linear correlation (albeit with a correlation coefficient of only 0.84) between increasing bulk phase shear viscosity and increasing foam stability as indicated by the average foam lifetime, Lp, which is defined as... 

The complex interfacial dilational modulus ( ) is a key fundamental property governing foam and emulsion stability. It is defined as the interfacial tension increment (da) per unit fractional interfacial area change (dA/A) i.e.,... 

The polymer material contains a linear ethylenic polymer having a melt flow ratio, 11012, of 5.63 or above, a MWD, Mw/Mn, defined by the equation Mw/Mn less than or equal to (I10/I2)-4.63 and a critical shear rate at onset of surface melt fracture of at least 50% greater than that of a linear olefin polymer having about the same 12 and Mw/ Mn. The foam structures have toughness and elasticity similar to those formed from conventional LLDPE without the poor dimensional stability and foam quality associated with those structures and foam quality similar... 

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