A presentation about foam in aerated food such as ice cream, whipped cream, marshmallow, etc.

1. 1
FOAMS!
Photo
courtesy
of
Dan
Phiffer
on
Flickr
Photo
courtesy
of
Leslie
on
Flickr
Photo
courtesy
of
Alpha
on
Flickr
Prof. Abd Karim Alias
Universiti Sains MalaysiaThis
work
is
licensed
under
a
Crea=ve
Commons
A@ribu=on-­‐NonCommercial-­‐ShareAlike
3.0
Unported
License.

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} 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

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} 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

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FOAM STRUCTURE
Abd Karim Alias, 2013

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FOAM STRUCTURE
Abd Karim Alias, 2013

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} 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

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} 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

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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

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FOAM FORMATION –Proteins as surface
active agent
Abd Karim Alias, 2013

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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

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• 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

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FOAM STABILITY : FOAM DRAINAGE
• As water leaves,
faces of film are
brought closer
together
Click picture to view animation
Abd Karim Alias, 2013

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• 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

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} 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

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EGG FOAMS
Abd Karim Alias, 2013

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} 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

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} 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

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} 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

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} 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

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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