Foods foams

Treatment of ceUulose with acids results in preferential hydrolysis in the more accessible amorphous regions and produces a product known as microcrystalline ceUulose (MCC). MCC is used to prepare fat-free or reduced-fat food products, to strengthen and stabilize food foams, as a tableting aid, and as a noncalotic bulking agent for dietetic foods. It has GRAS status. 

Food typically is a complicated system with diverse interfaces. Stable air-water or oil-water interfaces are essential for the production of food foams and emulsions. Interface phenomena, therefore, attract great interest in the food industry. AFM provides enough resolution to visualize the interface structures, but it cannot be directly applied on air-liquid or liquid-liquid interfaces. Fortunately, the interface structure can be captured and transferred onto a freshly cleaved mica substrate using Langmuir-Blodgett techniques for AFM scan. Images are normally captured under butanol to reduce adhesion between the probe and the sample. Then, sample distortion or damage can be avoided (Morris et al, 1999). 

It is possible to write about designing a system to produce a stable foam on the basis of accumulated scientific knowledge. However, notably, the vast majority of food systems were the product of empiricism and serendipity It remains to be seen if advances in scientific understanding can produce any food foam that is as successful as a meringue. 

A situation that commonly occurs with food foams and emulsions is that there is a mixture of protein and low-molecular-weight surfactant available for adsorption at the interface. The composition and structure of the developing adsorbed layer are therefore strongly influenced by dynamic aspects of the competitive adsorption between protein and surfactant. This competitive adsorption in turn is influenced by the nature of the interfacial protein-protein and protein-surfactant interactions. At the most basic level, what drives this competition is that the surfactant-surface interaction is stronger than the interaction of the surface with the protein (or protein-surfactant complex) (Dickinson, 1998 Goff, 1997 Rodriguez Patino et al., 2007 Miller et al., 2008 Kotsmar et al., 2009). 

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 ... 

These foams can also have complex rheological properties. Specialized methods have been developed to deal with the pronounced slip that can be exhibited by food foams [823]. Some food foams exhibit strong yield stresses, as in products that have been whipped to the stiff peak stage. Whipping air into egg white is an example. Baking the stiff foam that results produces meringue. 

Soft Cellular solids with thick walls and very small air bubbles can exhibit a compressibility pattern similar to that of a dense solid see the discussion of marshmallows bellow. Marshmallows are such an example. However stmetural eoUapse unaccompanied by significant lateral expansion is a characteristic of the majority of solid food foams, regardless of whether their cells are open or closed and whether their cell wall material is brittle or complying ( soft ). 

In practice, attempting to change a food s density, even when the ingredients composition remains unchanged, may also induee straetural changes that may complicate the interpretation of the E vs. p plot. Also, in contrast with theoretical models in which the cells are uniform and their geometry is well-defined, the bubbles of real solid food foams have varying cell wall thiekness as well as a size distribution... 

Figure 12.6. Scheme showing the approximate length and lime-scales in important phenomena related to the formation of bubbles and stability of food foams. 

Assuming that structural data are available, and that a property has been correctly measured, the next problem is to establish a relationship. Fundamental models are preferred by engineers because tlrey are based on basic principles of physics and the physical chemistry of the described phenomenon. Once it is realized that foods are essentially composite hierarchical structures, we can borrow models and theories developed for nonfood systems and apply them. A good example is the adaptation of mechanical principles for the description of cellular solids, (Gibson and Ashby 1988) to the properties of solid food foams (Attenburrow et al. 1989 Warburton et al. 1990). Examples are provided in Chapter 10. 

---