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Carlos Bravo-DIaz* and Elisa Gonzalez-Romero
Following the ideas pointed out in our previous work (1) about how food properties can be visualized with the aid of simple and inexpensive experiments using dairy products that can be found in any kitchen, and using almost exclusively kitchen materials, we have developed new ones to investigate the properties of food foams.
It is remarkable that a variety of solid foods, most notably bakery products, have a porous and open macrostructure resulting from a dispersion of gas bubbles into a matrix. These kinds of foods are usually referred to as foams and sponges and are low-density, porous, thin-walled structures. The main difference between foams and sponges is that sponges are capable of imbibing large quantities of solvent without dissolving, whereas foams do not have that property and would normally dissolve in the presence of water.
Typical dairy food foams and sponges with widely differing textures, such as meringues, cakes, marshmallow, souffles, mousses, bread, and ice-cream, can be easily found in the bakery or frozen foods section of any supermarket. In many cases, the gas is air (occasionally carbon dioxide) and the continuous phase is an aqueous solution or suspension containing proteins.
Foams and emulsions are related by the fact that each represents a physical state in which one fluid phase is dispersed in a second phase (2, 3). In foams, a continuous phase of thin layers, called lamellae, separates the gas bubbles. As with emulsions (1, 2), mechanical energy is required to create this interface. Maintaining the interface against coalescence of gas bubbles usually necessitates the presence of surface-active agents (2, 4, 5), which lower the interfacial tension and form an elastic protective barrier between entrapped gas bubbles.
Foams can be classified into two morphological groups (2, 3), spherical foams ("kugelschaum") and polyhedral foams ("polyederschaum") and can vary greatly in size (6) (usually from 1 gm to several centimeters). There are three major methods to prepare foams (4): (i) bubbling gas through a porous sparger into an aqueous solution of low protein concentration; (ii) beating (whipping) or shaking an aqueous protein solution in the presence of a bulk gas phase; and (iii) sudden release of pressure from a previously pressurized solution.
Experimental Procedures, Results and Discussion
The proposed...