The document discusses different types of colloidal systems including emulsions, sols, gels, and foams. It provides examples of each type in foods such as salad dressing as an emulsion, gravy as a sol, baked custard as a gel, and egg white foam as a foam. It also describes key properties of colloids like small particle size visible only under microscope and Brownian motion. Common colloidal systems in foods, properties of each type, and methods of formation and stabilization are summarized.

1. Neetu Gouda
Msc. 1st yr

3. The word colloids has actually derived from Greek
word “kola” where it means glue like.
The science of colloids was founded about 1861 by
Thomas Graham.
In his summary of work , he classified substances into
two groups viz: crystalloids and colloids ,depending on
their ability to diffuse through parchment membrane.
According to Graham , crystalloids readily passed
through parchment membranes while colloids do not.it
possess a size of diameter greater than 1 mu and less
than 100 mu.

4. COLLOIDS
Colloids are the particles that are too large to dissolve but remain dispersed in
the liquids. The term colloid doesn’t indicate a kind of matter, but a state of
matter. All colloidal systems have two phases:
A continuous phase extends throughout the system, surrounding all parts of
the other phase of the system.
The discontinuous phase or the discontinuous phase is, as the name implies,
distributed in isolated or disconnected fashion throughout the entire colloidal
system.

5. Colloidal systems in foods:
Name of colloidal system Dispersed phase Continuous phase Example in foods
EMULSION LIQUID LIQUID SALAD DRESSING
SOL SOLID LIQUID GRAVY
GEL LIQUID SOLID BAKED CUSTARD
FOAM GAS LIQUID EGG WHITE FOAM
SUSPENSOID GAS SOLID CONGEALED WHIPPED CREAM

6. Name of
colloidal
system
Disperse
d phase
Continuo
us phase
Example
in foods
EMULSI
ON
LIQUID LIQUID SALAD
DRESSIN
G
SOL SOLID LIQUID GRAVY
GEL LIQUID SOLID BAKED
CUSTARD
FOAM GAS LIQUID EGG
WHITE
FOAM
SUSPENS
OID
GAS SOLID CONGEA
LED
WHIPPE
D
CREAM
Properties of colloids:
Particles are visible only by ultra microscope or electron microscope – Brownian
motion.
 They do not sediment, and pass through common filters ( but not through
semipermeable membrane).
 Dispersion of passing light (Tyndall efect).
 Produce osmotic pressure.
Colloids are everywhere
 In the human body
Washing powder, soup, tooth paste, etc.
 Many foods ( yogurt, butter, milk)
 Nanotechnologies are based on chemistry of
colloids

7. TYNDALL EFFECTS: In a colloidal solution, the dispersed particles are
sufficiently large to scatter and polarize the incident light to same extent. This is
known as the tyndall effect. The effect is more pronounced in lyophobic sols than
in lyophilic sols.
NATURAL TYNDALL EFFECT
WHEN THE SUNRAYS ENTER THE FOREST CANOPY, TYNDALL
EFFECT CAN BE OBSERVED DUE TO THE DUST PARTICLES IN
THE ATMOSPHERE WHICH HELPS IN SCATTERING OF LIGHT.

8. BROWNIAN MOTION: When viewed through an ultra microscope , colloidal
particles appear to be in a state of rapid and irregular motion called the Brownian
movement. The movement is caused by the constant bombardment of the dispersed
particles by the molecules of the dispersion medium .It is zigzag vibration of the
dispersed particles .The smaller the size of the colloidal particles. The more vigorous
is its Brownian motion.

9. CLASSIFICATION OF COLLOIDS:
Colloids are classified into two groups :
1.] Lyophobic colloids: Includes those colloids
which have affinity for water. Eg. Inorganic
colloids.
Negative charge of S2- or HS- is
compensated by opposite charge from
the (H+).

10. 2.] Lyophilic colloids: Includes organic colloids
such as protein , starch , which have great
affinity to water.

11. CHARGE ON COLLOIDAL PARTICLES:
All colloids possess an electrical charge which
may be either positive or negative. In a given
colloidal system, all particles have like charges
and hence tend to repel one another and remain
in suspension. To be in suspension state, the
colloidal particles distribute themselves
uniformly throughout the liquid in which they
are dispersed.
Colloidal systems with two phases can occur in
eight different combinations so colloidal
systems are not restricted to the dispersion of
solid in liquid only. Each of the three states of
matter can be dispersed in a medium which may
be gaseous, liquid or solid.

12. 1.EMULSION: A mixture of two or more immiscible liquids. one liquid
(the dispersed phase) is dispersed in the other (the continuous phase). Three
substance are required to produce an emulsion: two immiscible liquids and
an emulsifying agent.
Prepared by shaking – oil/water (milk), water/ oil (butter).

13. Structure of emulsions: When a liquid e.g. oil is dispersed in
another immiscible liquid e.g. water(continuous phase) by mechanical
agitation , an emulsion is obtained.
Most of the dispersed droplets in food emulsions have diameters
between 0.1 and 10 micrometer.
Classification of emulsions – emulsions can be broadly
divided into two groups :
1) Oil in water type – Oil in water type emulsions
consist of fat dispersed in water e.g. milk.
2.) Water in oil type – water in oil type emulsions are
cream , butter , mayonnaise etc.

14. Some examples of food emulsions and uses:
 Milk is an emulsion of oil in water type and consists of fat dispersed in
water; the emulsifying agent being albumin and casein .
 Cod liver oil is an emulsion of oil in water type in which egg yolk ,
casein , gums have been added as emulsifier.
 Butter is an emulsion of water dispersed in fat.

15. Properties of emulsions: • The opacity of an emulsion is determined by droplet sizes , droplet
concentration and difference in the refractive indices of the two phases.
• Emulsion is transparent when the refractive indices of the two liquids are the
same or when droplet diameter is 0.05micrometer or less.
• When the dispersed phase is increased to a volume greater than that of the
continuous phase the viscosity of the emulsion increases.
Formation of emulsions: • A stable emulsions is not formed by a mere mixing of the liquids .
• Because when it will be left for sometime the droplets in the dispersed
phase coalesce due to surface tension.
• Therefore emulsifier is added to the emulsions,which reduces the interfacial
tension and enhances the coalesce.
• Ex: Eggs yolk is incorporated in the emulsions since it contains lecithin , a
natural emulsifying agents.

16. Stability of emulsions: • Stability changes in food emulsions can occur through the processes of creaming
, flocculation and coalescence.
• Emulsions can be stabilised against creaming , flocculation and coalescence by
introducing a strong interfacial film around each droplets , adding electric
charges to the droplets surfaces and increasing the viscosity of the continuous
phase.
• E.g Hydrocolloids, plant gums and gelatin , act as stabalizers in oil-in-water
emulsions by increasing the viscosity of the continuous phase.
• sometimes by forming a strong interfacial film around droplets of thr dispersed
phase.
• Pectins , alginates , plant and seed gums, and cellulose derivatives, such as
carboxymethayl, hydroxypropyl and methylcellulose gums are used as stabilizers.
Norevo- Acacia gum

17. 1.SOLS : • Sols are the colloidal systems in which solid of colloidal dimensions is
dispersed throughout a liquid .
• This type of system has flow properties , which may range from rather
fluid to extremely viscous , barely flowing .
• Sol possessing a continuous aqueous phase , the colloidal particles have
an electrically charged surface.The ionized groups of protiens and
phospholipids can be sources of this charges.

18. • The resulting potential difference between the surface of the particles and
the solution is known as zeta potential.
• In lyophobic sols, there is little interaction between the dispersed phase
and the dispersion medium.
• The viscocity of the lyophilic sols is greater than that of the dispersion
medium and it increases in particle concentration and decreases in
increasing of teperature.

19. GELS: • Sols that have fairly high concentration of dispersed solids
change spontaneously into gels.
• The liquid phase is entrapped in the interstitial ares of this
structure, due to which the sols loses its fluidity and
becomes a gel.
• Bonds present in the junction zones of gel are electrostatic,
hydrophobic ,covalent and hydrogen bond.
• Some of the free liquid ma be released if the gel structure
is cut.Drainage of free liquid from a gel is termed as
Syneresis.

20. Characteristics of gels:
• The concentration of the jelling agent ,the salt content ,
the pH and temperature determine the strength , elasticity
and brittleness of the gel.
• All gels can be destroyed by mechanical action ,but some
of them will set again after the agitation stops,such gels
said to be thixotropic.

21. FOAMS: • Foams are dispersions of gas bubbles in a liquid which is in the
continuous phase .
• The diameters of the foam bubbles range from about 1 micrometer to
several centimeters. Depending on the bubble size and wall thickness,
dense or light foams are formed.
• Food foams contain large amounts of entrapped gas.

22. Formation of foams: • Liquid capable of forming foams have low surface tension and
thus can spread or stretch easily and so not coalesce readily.
• For the formation of a foam there must be a foaming agent in
the continuous phase prior to dispersion of gas.
• The foaming agent must be absorbed at the surface to reduce
surface tension and provide a distinct surface layer which
resists the coalescence of gas bubbles.
• Surface active lipids, glucosides, cellulose derivatives and
protein are used as foaming agents.
• Defoaming agents : Several liquids will destroy foams ; ether,
toulene, the aliphatic alcohols , and some oil breaks most
foams.

23. Foam stability: • Foam stability can be enhanced by increasing the elasticity of the
bubble walls, by increasing the viscosity of the solution.
• This can be done by introducing gums and proteins, such as
gelatin. Foaming agents also helps in the stability of foam.
• Protein coagulum has a high water binding capacity and thus
contributes a decrease in the rate of drainage from foam.