1. 1 FOAMS! PhotocourtesyofDanPhieronFlickr PhotocourtesyofLeslieonFlickr PhotocourtesyofAlphaonFlickr Prof. Abd Karim Alias Universiti Sains MalaysiaThisworkislicensedunderaCrea=veCommons A@ribu=on-NonCommercial-ShareAlike3.0UnportedLicense.

2. 2 } Foam is a two-phase system in which the gas (air) phase is dispersed in a small amount of liquid (water) continuous phase. } Foam is desirable in beer; it is also promoted in whipped egg white (e.g., for making cakes, meringue, etc.), ice cream, marshmallow, etc. FOAM: DEFINITION & CHARACTERISTICS Abd Karim Alias, 2013 3. 3 } A bubbly foam (e.g. in ice cream) is formed when the amount of gas incorporated is low enough for bubbles to retain roughly spherical shape. } Polyhedral foam (e.g., beer foam) the gas- to-liquid ratio is so large that bubbles are pressed against one another in a honeycomb- type structure. FOAM STRUCTURE Abd Karim Alias, 2013 4. 4 FOAM STRUCTURE Abd Karim Alias, 2013 5. 5 FOAM STRUCTURE Abd Karim Alias, 2013 6. 6 } Three process steps for foam formation: air has to be injected into the liquid (e.g. using a mixer) large air bubbles have to be broken up into smaller bubbles the smaller bubbles have to be prevented from fusing during the formation of a foam FOAM FORMATION Abd Karim Alias, 2013 7. 7 } A surface active foaming agent is essential for the formation of stable foam } The foaming agent lowers the surface tension of the liquid phase & allows expansion of its surface area. } The surfactant forms a closely packed film around the dispersed gas bubbles. FOAM FORMATION The role of surface active agent Abd Karim Alias, 2013 8. 8 Three processes involved in the stabilization of protein foams: } adsorption of the protein at the gas- liquid interface, } surface denaturation, } coagulation of protein. FOAM FORMATION Proteins as surface active agent Abd Karim Alias, 2013 9. 9 FOAM FORMATION Proteins as surface active agent Abd Karim Alias, 2013 10. 10 Three factors affecting foam stability: drainage: the draining of liquid from foam disproportionation: the change in foam bubble size distribution caused by gas diffusion from small to large bubbles coalescence: the fusion of foam bubbles FOAM STABILITY Abd Karim Alias, 2013 11. 11 Water drains from foam under gravity A foam drains along lamellae to the curved junction of thin lamellae (plateau borders), where the pressure is lower. FOAM STABILITY : FOAM DRAINAGE Abd Karim Alias, 2013 12. 12 FOAM STABILITY : FOAM DRAINAGE As water leaves, faces of film are brought closer together Click picture to view animation Abd Karim Alias, 2013 13. 13 The diffusion of gas from small bubbles into big bubbles is referred to as disproportionation. In the absence of a stabilizing film of polymer molecules, disproportionation occurs remarkably quickly. Probably the most important type of instability in foams. FOAM STABILITY : Disproportionation Abd Karim Alias, 2013 14. 14 } Egg foams (egg white) are essential in the preparation of angel cakes, sponge cakes, meringues, souffles, etc. } The proteins not only lower the surface tension of egg white but some are denatured at the surface. } The coagulation of proteins at the gas-liquid interface form a network that gives some rigidity & stability to the foam. EGG FOAMS Abd Karim Alias, 2013 15. 15 EGG FOAMS Abd Karim Alias, 2013 16. 16 } Globulins appeared to be good foamers, producing small gas bubbles & a large volume. } Ovomucin is not a good foamer by itself but stabilised the foam because it is rapidly insolubilised (denatured) at the bubble surface. } The presence of fat, even in small amounts, and egg yolk, have a detrimental effect on foam formation. EGG FOAMS Abd Karim Alias, 2013 17. 17 } The presence of lipids retards foaming because the oil molecules migrate to the air-water interface before the protein molecules, inhibiting the unfolding of the protein & thus the formation of foam. } The antifoaming behavior of egg yolk is partly due to the presence of lecithin, which is believed to bind to egg white proteins, preventing them from associating at the air-water interface, & competitively displacing them from the interface. EGG FOAMS Abd Karim Alias, 2013 18. 18 } Increase of [protein] increases both the foamability & foam stability, mainly because of viscosity effect which produces a thicker lamella film. } Adjusting egg white pH to 6.5 by adding an acid ingredient increases foam stability to heat, because the acid makes foam less prone to over-coagulation. } Sugars enhance foam stability by increasing the viscosity of lamellar fluid which reduces the drainage rate. EGG FOAMS Abd Karim Alias, 2013 19. 19 } In fact, foams can cause many problems, including vessels overflowing, processing and packaging interference, damaging materials and housekeeping issues } Silicon dioxide is the most common chemical used in defoamers and antifoams, as it can destroy and suppress processing foams. FOAMS ARE NOT ALWAYS DESIRABLE! Abd Karim Alias, 2013 20. 20 Knowing when to produce foam and when to get rid of it are one of the many keys to product success! Abd Karim Alias, 2013