Colloidal Systems in Food Products
Functions
of
Colloidal
Systems
in
Food
Products
Mrs. Rajesh Kumari
Deptt. of Food Technology
C.B.L. Govt. Polytechnic, Bhiwani
L
e
a
r
ni
n
g
o
b
j
e
c
t
i
v
e
s
•
To
d
e
fin
e
co
lloi
d
a
l
s
y
s
t
e
m
s
.
•
To
ex
p
l
a
i
n
t
he
di
f
f
e
r
en
c
e
b
e
tw
een
a
so
l
an
d
a
g
el.
•
To
u
n
d
e
r
s
t
a
n
d
h
o
w
em
u
l
s
io
n
s
a
r
e
f
o
r
me
d
.
•
To
d
e
fin
e
a
n
d
re
c
o
g
n
i
s
e
e
x
a
m
p
le
s
o
f
f
o
a
ms
.
Wha
t
a
re
co
ll
o
i
da
l
s
y
s
t
e
m
s
?
Colloidal
systems
give
structure,
texture
and
mouthfeel
to
many
different
products,
for
example:
The
functions
of
colloidal
systems
can
be
used
in
a
variety
of
ways
in
order
to
produce
food
products.
j
a
m
i
ce
c
r
e
a
m
m
a
y
o
nn
a
i
s
e
Wha
t
a
re
co
ll
o
i
da
l
s
y
s
t
e
m
s
?
Colloids
are
formed
when
one
substance
is
dispersed
through
another,
but
does
not
combine
to
form
a
solution.
There
are
many
types
of
colloidal
systems
depending
on
the
state
of
the
two
substances
mixed
together.
Gels,
sols,
foams
(e.g.
egg
white
foam)
and
emulsions
(e.g.
butter)
are
all
types
of
colloids.
The
substance
which
is
dispersed
is
known
as
the
disperse
phase
and
is
suspended
in
the
continuous
phase.
Egg
white
foam
is
an
example
of
this.
Air
bubbles
(disperse
phase)
are
trapped
in
the
egg
white
(continuous
phase)
resulting
in
a
foam.
Functions
of
colloidal
systems
in
food
products
Most
colloids
are
stable,
but
the
two
phases
may
separate
over
a
period
of
time
because
of
an
increase
in
temperature
or
by
physical
force.
They
may
also
become
unstable
when
frozen
or
heated,
especially
if
they
contain
an
emulsion
of
fat
and
water.
Ma
i
n
t
y
p
es
o
f
c
o
l
l
o
i
d
al
s
y
st
e
m
S
o
ls
a
n
d
g
e
ls
Sols
and
gels
are
both
liquid
loving
(lyophilic)
colloids.
A
sol
is
a
liquid
colloid
or
mixture
in
which
solid
particles
are
dispersed
in
a
liquid
phase.
The
disperse
phase
is
attracted
to
molecules
of
the
continuous
phase.
Sometimes
the
mixture
needs
to
be
heated
and
stirred.
When
this
solution
cools,
the
sol
changes
into
a
gel,
which
resembles
a
solid
rather
than
a
liquid.
Both
protein
and
starch
can
be
used
in
the
formation
of
a
sol
or
gel.
S
o
ls
a
n
d
g
e
ls
When
a
jelly
is
made,
gelatine
is
dispersed
into
a
liquid
and
heated
to
form
a
sol.
As
the
sol
cools,
protein
molecules
unwind
forming
a
network
that
traps
water
and
forms
a
gel.
If
cornflour
is
mixed
with
water
and
heated,
the
starch
granules
absorb
water
until
they
rupture,
the
starch
then
disperses
in
the
water
and
the
mixture
becomes
more
viscous
and
forms
a
gel
on
cooling.
O
t
he
r
t
y
p
e
s
o
f
g
e
l
Other
types
of
gel
are
formed
with
pectin
and
agar.
Pectin,
a
form
of
carbohydrate
found
in
fruits,
is
used
in
the
production
of
jam
to
help
it
set.
However,
for
it
to
gel
there
must
be
at
least
50%
sugar
and
conditions
should
be
acidic.
Agar
is
a
polysaccharide
extracted
from
seaweed
which
is
capable
of
forming
gels.
If
a
gel
is
allowed
to
stand
for
a
time,
it
starts
to
‘weep’.
This
loss
of
liquid
is
known
as
syneresis.
E
mul
s
i
ons
When
water
and
oil
are
shaken
together,
they
form
an
emulsion.
This
emulsion
is
unstable.
If
left
to
stand,
the
oil
will
form
a
separate
layer
on
top
of
the
water,
e.g.
traditional
French
dressing.
The
two
liquids
are
immiscible
(they
will
not
mix
together).
A
stable
emulsion
is
formed
when
two
immiscible
liquids
are
held
stable
by
a
third
substance,
called
an
emulsifying
agent.
E
m
u
l
s
i
o
ns
An
emulsion
may
be
oil-in-water
(o/w)
in
which
case
small
oil
droplets
are
dispersed
through
water,
e.g.
milk,
or
water-in-oil
(w/o)
in
which
case
small
water
droplets
are
dispersed
through
oil,
e.g.
butter.
E
mul
s
i
ons
An
emulsifying
agent
is
made
up
of
two
parts.
One
is
hydrophilic
(water
loving)
and
the
other
is
hydrophobic
(water
hating).
The
emulsifier
holds
the
disperse
phase
within
the
continuous
phase.
This
results
in
the
emulsion
becoming
stable.
E
mul
s
i
ons
Mayonnaise
is
an
example
of
a
stable
emulsion
of
oil
and
vinegar,
when
egg
yolk
(lecithin)
may
be
used
as
an
emulsifying
agent.
Stabilisers
are
often
added
to
emulsions
to
increase
the
viscosity
of
the
product.
These
help
improve
the
stability
of
the
emulsion,
as
over
time
the
emulsion
may
separate.
Stabilisers
also
increase
shelf
life,
E461
methylcellulose,
used
in
low
fat
spreads.
F
o
a
m
s
Foams
are
composed
of
small
bubbles
of
gas
(usually
air)
dispersed
in
a
liquid,
e.g.
egg
white
foam.
As
liquid
egg
white
is
whisked,
air
bubbles
are
incorporated.
The
mechanical
action
causes
albumen
proteins
to
unfold
and
form
a
network,
trapping
the
air.
If
egg
white
is
heated,
protein
coagulates
and
moisture
is
driven
off.
This
forms
a
solid
foam,
e.g.
a
meringue.
Ice
cream,
bread
and
cake
are
other
examples
of
solid
foams.
Re
v
i
e
w
o
f
t
h
e
l
e
a
r
n
in
g
o
b
j
ec
t
i
v
e
s
•
To
d
e
fin
e
co
lloi
d
a
l
s
y
s
t
e
m
s
.
•
To
ex
p
l
a
i
n
t
he
di
f
f
e
r
en
c
e
b
e
tw
een
a
so
l
an
d
a
g
el.
•
To
u
n
d
e
r
s
t
a
n
d
h
o
w
em
u
l
s
io
n
s
a
r
e
f
o
r
me
d
.
•
To
d
e
fin
e
a
n
d
re
c
o
g
n
i
s
e
e
x
a
m
p
le
s
o
f
f
o
a
ms
.
Colloidal systems play a crucial role in providing structure, texture, and mouthfeel to various food products such as jam, ice cream, and mayonnaise. They are formed when one substance disperses through another without forming a solution, resulting in various types of colloids like gels, sols, emulsions, and foams. These systems are essential for the stability and overall quality of food products but can become unstable under certain conditions like temperature changes. Sol-gel transformations are common in colloidal systems, impacting the final texture of the food product.
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Presentation Transcript
Functions of Colloidal Systems in Food Products Mrs. Rajesh Kumari Deptt. of Food Technology C.B.L. Govt. Polytechnic, Bhiwani
Learning objectives To define colloidal systems. To explain the difference between a sol and a gel. To understand how emulsions are formed. To define and recognise examples of foams.
What are colloidal systems? Colloidal systems give structure, texture and mouthfeel to many different products, for example: jam ice cream mayonnaise The functions of colloidal systems can be used in a variety of ways in order to produce food products.
What are colloidal systems? Colloids are formed when one substance is dispersed through another, but does not combine to form a solution. There are many types of colloidal systems depending on the state of the two substances mixed together. Gels, sols, foams (e.g. egg white foam) and emulsions (e.g. butter) are all types of colloids. The substance which is dispersed is known as the disperse phase and is suspended in the continuous phase. Egg white foam is an example of this.Air bubbles (disperse phase) are trapped in the egg white (continuous phase) resulting in a foam.
Functions of colloidal systems in food products Most colloids are stable, but the two phases may separate over a period of time because of an increase in temperature or by physical force. They may also become unstable when frozen or heated, especially if they contain an emulsion of fat and water.
Main types of colloidal system Disperse phase Continuous phase System Product Uncooked custard, unset jelly Jelly, jam, blancmange Sol Solid Liquid Gel Liquid Solid Mayonnaise, milk Emulsion Liquid Liquid Solid emulsion Foam Butter, margarine Liquid Solid Whipped cream, whisked egg white Meringue, bread, cake, ice cream Gas Liquid Solid foam Gas Solid
Sols and gels Sols and gels are both liquid loving (lyophilic) colloids. A sol is a liquid colloid or mixture in which solid particles are dispersed in a liquid phase. The disperse phase is attracted to molecules of the continuous phase. Sometimes the mixture needs to be heated and stirred. When this solution cools, the sol changes into a gel, which resembles a solid rather than a liquid. protein used in the formation of a sol or gel. Both and starch can be
Sols and gels When a jelly is made, gelatine is dispersed into a liquid and heated to form a sol. As the sol cools, protein molecules unwind forming a network that traps water and forms a gel. If cornflour is mixed with water and heated, the starch granules absorb water until they rupture, the starch then disperses in the water and the mixture becomes more viscous and forms a gel on cooling.
Other types of gel Other types of gel are formed with pectin and agar. Pectin, a form of carbohydrate found in fruits, is used in the production of jam to help it set. However, for it to gel there must be at least 50% sugar and conditions should be acidic. Agar is a polysaccharide extracted from seaweed which is capable of forming gels. If a gel is allowed to stand for a time, it starts to weep . This loss of liquid is known as syneresis.
Emulsions When water and oil are shaken together, they form an emulsion. This emulsion is unstable. If left to stand, the oil will form a separate layer on top of the water, e.g. traditional French dressing. The two liquids are immiscible (they will not mix together). A stable emulsion is formed when two immiscible liquids are held stable by a third substance, called an emulsifying agent.
Emulsions An emulsion may be oil-in-water (o/w) in which case small oil droplets are dispersed through water, e.g. milk, or water-in-oil (w/o) in which case small water droplets are dispersed through oil, e.g. butter.
Emulsions An emulsifying agent is made up of two parts. One is hydrophilic (water loving) and the other is hydrophobic (water hating). The emulsifier holds the disperse phase within the continuous phase. results in the emulsion becoming stable. This
Emulsions Mayonnaise is an example of a stable emulsion of oil and vinegar, when egg yolk (lecithin) may be used as an emulsifying agent. Stabilisers are often added to emulsions to increase the viscosity of the product. improve the stability of the emulsion, as over time the emulsion may separate. Stabilisers also increase shelf life, E461 methylcellulose, used in low fat spreads. These help
Foams Foams are composed of small bubbles of gas (usually air) dispersed in a liquid, e.g. egg white foam. white is whisked, air bubbles are incorporated. As liquid egg The mechanical action causes albumen proteins to unfold and form a network, trapping the air. If egg white is heated, protein coagulates and moisture is driven off. This forms a solid foam, e.g. a meringue. Ice cream, bread and cake are other examples of solid foams.
Review of the learning objectives To define colloidal systems. To explain the difference between a sol and a gel. To understand how emulsions are formed. To define and recognise examples of foams.
