The document provides an overview of food colloids, focusing on their definitions, classifications, and functionalities, including emulsions, gels, and foams. It discusses the structural components of food colloids, their formation processes, and the role of emulsifiers and stabilizers in achieving desired textures and consistency in various food products. Understanding these colloidal systems is crucial for food technologists to manipulate and enhance the properties of food.

1. DAVID TRYSON TEMBO, PhD
MUBAS, PBS, MALAWI
1
PBS-FCH-311
FOOD COLLOIDS

2. Lecture overview
• Definitions: Colloid, phase, and colloidal
systems
• Food Colloids - classification
• Emulsions and emulsifiers
• Sols and gels
• Foams

3. Learning outcomes
• At the end of this session, you should be able to:
– Describe what gels, emulsions and foams are and
give food examples of each
– Link key drivers and quality parameters (texture) to
the structure of a number of food products
– Discuss the functionality of phospholipids and
proteins in the structure and texture of emulsions
and foams

4. What is a colloid?
"A colloid is a dispersion of large
molecules through a continuous phase"

5. What is a phase?
• A phase is a homogeneous amount of matter

6. Colloidal Systems
• Colloidal system: made up of large molecules of a
substance dispersed in a continuous phase
Think of it as "the container and the contained"
• The continuous phase (container) can be
• Liquid
• Solid
• The disperse phase (contained) may be:
• Solid
• Liquid
• Gaseous

7. Food colloids
Continuous phase: water
Dispersed phase: proteins, lipids, sugars
Continuous phase: oil
Dispersed phase: water
Most foods are multi-phase systems

8. Food colloids
• The main molecular components of food colloids are
proteins, lipids and polysaccharides.
• Colloids consist of particles substantially larger than atoms
but too small to be visible to the naked eye (10-7 to 10-3 m)

9. • Colloid: any substance consisting of
particles substantially larger than atoms or
ordinary molecules but too small to be
visible to the unaided eye (10-7 to 10-3 m)
Dispersed phase
Continuous
phase
Gas Liquid Solid
Gas N/A Liquid aerosol
Hair sprays
Solid aerosol
Liquid Foam
Cappuccino foam
Emulsions
Milk - Mayonnaise
Sol
Starch in water
Solid Solid foam
Meringue - Bread -
Ice cream
Gel / Solid Emulsions
Jellies / Butter
Solid sol

10. Emulsion
Foams
Gels
Emulsion
Emulsion

11. Solutions, dispersion and
suspension
Solution: the dissolved substance is < 1 nm (10-9 m) in
size (e.g. sucrose solution): not a colloid
SIZE!
Dispersion: the particles are between 1 nm and
1 m in size (e.g. proteins, starch)
Suspension, if the particles are > 1 m (10-6 m)
in size (e.g. flour in cold water)

12. Emulsions
• The surface tension causes a liquid to assume the
minimal surface area
• When we mix water and oil we increase the area of
contact
• Can be defined as
• O/W (salad dressing)
• W/O (Butter, Margarine)

13. Emulsions
– Oil-in-water (o/w)
• Oil droplets forming the disperse phase are dispersed
throughout the water
– Water-in-oil (w/o)
• Water droplets are dispersed through the oil
Oil droplets

14. Destabilized emulsions
Flocculation: small particles come
together form aggregates (reversible)
Coalescence: particles merge forming
larger spheres (irreversible)
Creaming: aggregates float / sink -
less dense than continuous phase
Breaking: separation of
phases

15. Emulsifiers
• To form a stable emulsion a third substance
called an emulsifying agent or emulsifier is
added
• Emulsifiers act by lowering the interfacial
tension
• The emulsifier becomes adsorbed at interface
and lowers the surface tension making the
system more stable

16. Emulsifiers
• Emulsifier molecules contain a hydrophilic and a
hydrophobic group
– The hydrophillic group is polar and is attracted to water
– The hydrophobic group is non-polar and is attached to
the oil
Hydrophillic
group
Hydrophobic
group

17. Nature of the emulsion
• The type of emulsion formed depends on a
number of factors:
– composition of oil and water phase
– proportions of oil and water
– chemical nature of emulsifier
• HLB (hydrophilic-lipophilic balance) is used to
choose a suitable emulsifier

18. Natural emulsifiers
• Phospholipids
– Lecithin (HLB values 4 to 9)
• Proteins
– Casein in milk
• Carbohydrates
– Acacia gum in fizzy drinks

19. Proteins as emulsifiers
• Diffusion to the interface
• Energy of the system is lowered by
– Having hydrophobic parts of the molecule
sticking into the organic (oil) phase
– The hydrophilic part remaining in the aqueous
phase
– Adsorption occurs, protein is denatured Water
Oil

20. Artificial emulsifier
• Glycerol monostearate (GMS)
– E471
Hydrophilic
Hydrophobic

21. Food emulsions
Example Type Main emulsifiers
Milk, Cream o/w Proteins (casein)
Butter w/o Proteins (casein)
Mayonnaise, Salad
cream
o/w Egg-yolk (lecithin), GMS, mustard
Margarine w/o Proteins (casein), lecithin, GMS
Ice cream o/w Proteins (casein), GMS plus stabilisers
(gums, alginates)

22. Strategies for low fat products
• Creamy mouthfeel linked to oil droplet size and
number
• Evidence that droplets are not sheared in the mouth
• Double or duplex emulsions to “empty” droplets of fat
Water
Oil

23. Sols and Gels
• A sol is a solid in a liquid (e.g. starch in warm water)
– The dispersed phase is formed by high MW molecules
(e.g. starch, protein)
– A sol can set to a gel if the concentration of DP is high
enough
• A gel is a liquid in a solid (e.g. jellies, jams, custard)
– The liquid phase (e.g. water and dissolved solids) is
dispersed in a solid network of polymer chains (high
MW molecules) such as gelatine, pectin, gums, starches,
which 'trap' the liquid
– They have stable structures and retain their shape

24. Gels - Gelatine
Gelatine forms thermo-reversible gels
Insoluble in cold water
Soluble in hot water

25. Stabilisers
• Prevent coalescence, creaming,
flocculation or breaking by increasing the
viscosity
– Pectins
– Starch
– Alginate

26. Gels – Starch - Alginate –
Carrageenan – Pectin
• Technological aims:
– Increase viscosity: creaminess / mouthfeel
– Improve freeze / thaw stability
– Increase water retention
• Thickeners
• Ferran Adrià
– Liquid olives
http://youtu.be/gKWgmx0kc1A

27. Foams
•Liquid Foam
• Gas dispersed in liquid
• e.g. whipped cream, beaten egg-white
•Solid Foam
• Gas dispersed in a solid
• e.g. ice cream, marshmallows
•Foams consist of an agglomeration of gas
bubbles separated by thin films

28. Foams
• Critical for product quality
– Ice cream / Cappuccino / Bread
• Aeration can be achieved by:
– whipping air in
– chemical reaction produces gas e.g. baking
powder produces CO2
– yeasts ferment food (sugar) to produce CO2

29. Foaming agents
• Foaming agents are required in order for
the foam to remain intact.
• They form a cohesive, deformable film
around the air bubbles.
• Similar mechanism as for emulsions
– Decrease surface tension

30. Foaming agents
• Proteins:
– Absorption at the interface, denaturation
• Cellulose derivatives
– CMC (carboxymethyl cellulose)
SDS

31. Foam stability and protein
iso-electric point
• Foam stability is enhanced when pH is
close to the i.p. of the proteins
– The proteins readily denature
• Lower the pH to reach the isoelectric point
– small amounts of acidic materials (e.g. lemon juice,
cream of tartar or vinegar) can be used to lower pH

32. Foamed foods
• Bread, ice-cream, whipped cream…
• Mint gazpacho with bacon and mushroom
foam

33. Structure in relation to sensory
properties
Food Structure
• Droplet size
• Droplet number
• Emulsifier type
• Viscosity
• Macromolecule type
• …..
Oral Processing
• Mechanical process
• Enzymes
• Chemical process
• Temperature
Sensory Properties
• Hardness
• Brittleness
• Viscosity
• Gumminess
• Chewiness
• Adhesiveness
• Grittiness
• Mouth coating

34. QUIZ
Take a paper (can be very small);
do NOT write your name on it

35. 1. In a solution, the substance that is being dissolved
is called?
a. solvent
b. emulsifier
c. solute
d. filtrate
2. An example of a colloid which is an
emulsion:
a. Whipped cream
b. Mayonnaise
c. Gelatin
d. Black coffee

36. 3. A glycerol backbone with 1 or 2 fatty acids plus another
group, possibly a phosphorous group produce?
a. sterol
b. trans fatty acid
c. phosphoric acid group
d. phospholipid
4. Which of the following is NOT an emulsifier:
a. triglyceride
b. bile acids
c. lecithin
d. monoglyceride

37. Answers
Swap papers with the person next
to you

38. 1. In a solution, the substance that is being dissolved
is called?
a. solvent
b. emulsifier
c. solute
d. filtrate
2. An example of a colloid which is an
emulsion:
a. Whipped cream
b. Mayonnaise
c. Gelatin
d. Wine

39. 3. A glycerol backbone with 1 or 2 fatty acids plus another
group, possibly a phosphorous group produce?
a. sterol
b. trans fatty acid
c. phosphoric acid group
d. phospholipid
4. Which of the following is NOT an emulsifier:
a. triglyceride
b. bile acids
c. lecithin
d. monoglyceride

40. Take Away Message
• Colloids are important structures which
are found in foods.
• Emulsions are mixtures of immiscible
liquids which constitute a major groups
of food products.
• Foams are mixtures of gases in a
continuous solid or liquid phase.
• Understanding colloid behaviour
enables technologist to alter the
properties of food products.

41. Further Reading
• Dickinson, Eric (1987) Food emulsions
and Foams, Royal Society of Chemistry.
London.