Stability foams, overrun

In contrast to protein stabilized foams the foam formation and stabilization mechanisms in whipping cream are supposed to depend on the bubble stabilization by means of fat rather than proteins. The fat content can therefore not be less than 30% butterfat, and whipping cream is expected to fulfil certain criteria, namely whipping time, foam firmness, foam volume increase (or overrun), and volume of dripping-off (or drainage). 

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 ... 

Ice cream is a partially frozen foam that is also an emulsion and a suspension, containing many components including proteins, fat, water, and air. A typical ice cream mix might contain milk fat (10-16%), milk solids-not-fat2 (9-12%), sugars (9-12%), corn syrup solids (4-6%), stabilizers and emulsifiers (0-0.5%), and water [430,811,815], When prepared, ice cream may have an overrun (Section 13.3) of 70-100% (that is, it will contain 40-50 volume percent air) [811], see Table 13.2. Due to the partial freezing, ice cream also contains dispersed ice particles. At -11 °C ice cream has a viscosity of about 109 mPa s [215]. 

Lim et al. (2008a,b) demonstrated that application of high pressnre (300 MPa, 15 min) conld enhance the foaming properties of WPG, which was added to low-fat ice cream to improve its body and texture. Due to the impact of high pressure on the fnnctional properties of whey proteins, the ice-cream mix containing the pressnre-treated whey protein exhibited increased overrun and foam stability and hardness than ice cream produced with untreated whey protein. 

As with emulsion formation, the maximal absorption of proteins has been reported to occur near the isoelectric point [6,18,47], The effects of pH on the properties of proteins at emulsion surfaces, noted previously, probably also apply to the behavior of proteins in films. While foams formed near the isoelectric point of proteins tend to be more stable than those formed at other pH values, it is often possible to obtain higher overruns away from the isoelectric point [48]. The largest effect of pH on foam stability can probably be explained by the more viscoelastic nature of the films formed in this pH region... 

---