Emulsions and foams

Question 1

Colloidal system

Answer 1

contains one substance of microscopically dispersed insoluble particles is suspended throughout another substance.

Question 2

An emulsion is a

Answer 2

colloidal system containing two liquids or phases that normally do not mix (immiscible): a dispersed phase and a continuous phase.

Question 3

If water is the continuous phase

Answer 3

the emulsion is said to be an oil-in-water or o/w emulsion.
– salad dressings, mayonnaise

Question 4

If oil is the continuous phase the emulsion is termed a water-in-oil or w/o emulsion.

Answer 4

—butter, margarine

Question 5

Surface tension

Answer 5

is a property of the surface of a liquid that allows it to resist an external force

Question 6

If strong attractive forces among the molecules of liquid exist, then the force required to pull the molecules apart to expand the surface or to spread the liquid will be high.

Answer 6

Surface tension

Question 7

Interfacial tension

Answer 7

Is the term used when “surface tension” exists between two liquids, such as oil and water.

A high surface or interfacial tension makes it difficult to mix the liquid with another liquid.

Question 8

Emulsifiers are

Answer 8

surface-active molecules that are added to reduce the interfacial tension between two liquids.

Question 9

Emulsifiers exist at the surface of a liquid because

Answer 9

a section of the molecule is nonpolar and hydrophobic, while the other is polar and hydrophilic.

Question 10

Emulsifiers (Examples used in foods):

Answer 10

dry mustard
paprika
some proteins (dependent on their amino acid structure)
mono- and diglycerides

Question 11

Natural emulsifiers

Answer 11

-Best are proteins
-Uncoil or denature and absorb at the interface and interact to form a stable interfacial film
-Proteins of egg yolk are the best mayonnaise.

Question 12

Emulsifiers must be able to:

Answer 12

-Absorb at the interface between two liquid such as oil and water
-Reduce the interfacial tension of each liquid, enabling one liquid to spread more easily around the other.
-Form a stable, coherent, viscoelastic film
-Prevent or delay coalescence of the emulsion droplets.

Question 13

HLB scale

Answer 13

-developed by food scientist to determine the hydrophilic-lipophilic balance.
-a measure of the degree to which an emulsifier is hydrophilic or lipophilic

Question 14

Useful in helping in determining which emulsifier is most suited to the needs of food product developers.

Answer 14

HLB scale

Question 15

A value from 3 to 6 indicates a

Answer 15

W/O (water in oil) emulsifier

Question 16

A value from 8 to 16 indicates

Answer 16

O/W (oil in water) emulsifier

Question 17

Emulsion stabilizers

Answer 17

once formed, the droplets in an emulsion may be crowded and bump into each other or are forced up against each other.

The force of surface tension may pull them together and cause them to coalesce again

Question 18

Foams

Answer 18

if not formed properly, the resulting foam is unstable and results in a dense product with low volume

Question 19

Foams such as meringue and baked goods are

Answer 19

heat set, which denatures the protein and converts the liquid phase into a solid phase

Question 20

continuous phase has colloidal dimensions

Answer 20

foam

Question 21

the dispersed phase has colloidal dimensions

Answer 21

Emulsions

Question 22

an emulsion occurs when a

Answer 22

liquid traps fat in a structure, or fat traps liquids in a structure.

Question 22

foams are a structure that

Answer 22

traps air in bubbles

Question 23

foam formation

Answer 23

-energy must be applied
-to incorporate gas into the liquid
-to break up large bubbles into smaller ones
-to spread the liquid phase around the gas bubbles as they form.

Question 24

the higher the energy, the smaller the bubbles, and the GREATER the foam volume (w/foaming agent)

Answer 24

foam formation

Question 25

Foam volume:

Answer 25

depends on ability of foaming agent to absorb at the interface and reduce interfacial tension and the level of energy input during whipping

Question 26

Foam volume may be reduced due to:

Answer 26

-the tendency of the liquid film to drain due to gravity
-the tendency for the film to rupture an allow coalescence or escape of gas bubble.
-diffusion of gas from small bubbles to large ones causing the foam to shrink
-evaporation of the continuous phase.

Question 27

Foam stability

Answer 27

depends on the ability of the foaming agent to produce a stable interfacial film and a viscous continuous phase.

Question 28

Factors affecting foam stability

Answer 28

-drainage of the liquid film between gas bubbles.
-rupture of the interfacial film around gas bubbles.
-diffusion of gas from small to large bubbles.
-evaporation of the continuous phase.

Question 29

Foaming agents

Answer 29

when egg whites are whipped, the proteins denature at the interface and interact with one another to form a stable, viscoelastic, interfacial film

gelatin and milk protein are also good foaming agents

Question 30

Gelatin

Answer 30

good foaming agent
a warm gelatin sol can be whipped to 3 times its original volume
-when cooled, the gelatin, solidifies or forms a gel, trapping the air bubbles and stabilizes the foam
-marshmallow

Question 31

Effects of added ingredients, Foam Stabilizers:

Answer 31

gums, sugar, acids, starches

Question 32

Effects of added ingredients, Foam Destabilizers

Answer 32

lipids, phospholipids, salts

Question 33

Acid as a foam stabilizer

Answer 33

addition of acid reduces the pH, which reduces the charge on the protein molecules and usually brings them close to their isoelectric point

cream of tartar

generally results in a stronger, more stable interfacial film.

Question 34

Ice cream

Answer 34

stabilized by emulsified fat droplets and small ice crystals oriented within the continuous phase

Question 35

angle food cake:

Answer 35

contains solid particles in the form of flour, which are folded into the egg white/sugar foam, minimizing film drainage.
–The increased viscosity and presence of solid particles also reduces breakage of the interfacial film

Question 36

Foaming suppressants

Answer 36

absorb at the interface suppressing the adsorption of the desired foaming agent, preventing it from forming a stable foam, suppressing foam volume.

Question 37

egg yolks:

Answer 37

phospholipids and lipoproteins

Question 38

salt:

Answer 38

weakens the interfacial film around the gas bubbles.

Question 39

Antifoaming agents:

Answer 39

-are able to break up foams or prevent them from forming.
-commonly added to frying oils to prevent foaming during the frying process.
-act absorbing at the air/liquid interface to prevent foaming. foaming suppressants.