Foam is a two-phase system in which the gas (air) phase is dispersed in a small amount of liquid (water) continuous phase.

1. FOOD FOAM
MOHAMMAD MUHAIMINUL ISLAM
FOOD ENGINEERING
UNIVERSITY OF DEBRECEN

2. DEFINITION OF FOOD FOAM
 Foam is a two-phase system in which the gas (air) phase is dispersed in a small
amount of liquid (water) continuous phase.
 A foam is a substance that is formed by trapping many gas bubbles in a liquid or
solid. It can be considered a type of colloid.
 Foam is desirable in beer; it is also promoted in whipped egg white (e.g., for
making cakes, meringue, etc.), ice cream, marshmallow, etc.

3. STRUCTURE;
 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.

5. DILUTE FOAM;
 Somewhat similar to emulsions
 Various modes of formation
 Large (~mm) spherical bubbles
 Very fast creaming
 Ostwald ripening

6. CONCENTRATED FOAM;
 Distorted non-spherical gas cells
 Very high volume fraction, often >99%

7. FORMATION:
 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

8.  THE ROLE OF ACTIVE SURFACE AGENT ( FORMATION)
 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.

9.  PROTEIN AS SURFACE ACTIVE AGENT ( FORMATION)
Three processes involved in the stabilization of protein foams:
 adsorption of the protein at the gas- liquid interface,
 surface denaturation,
 coagulation of protein.

11. STABILITY;
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.

12. DRAINAGE :
• 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.
• As water leaves, faces of film are brought
closer together

13. DISPROPORTIONATION
 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.

14. EGG FOAM
 Egg foams (egg white) are essential in the preparation of angel cakes, sponge
cakes, meringues, soufflés, 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.

15.  Globulins appeared to be good
foamier, producing small gas bubbles
& a large volume.
 Ovomucin is not a good foamier by
itself but stabilized the foam because
it is rapidly insolubilized (denatured)
at the bubble surface.
 The presence of fat, even in small
amounts, and egg yolk, have a
detrimental effect on foam formation.

16.  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.

17.  Increase of [protein] increases both the formability & 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.

18.  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.
Knowing when to produce foam and when to get rid of it are one of the many
keys to product success!

21. Thanks for your time