lec 2 food dispersions

Question 1

what are Food Dispersions

Answer 1

Dispersions are physically heterogeneous multi-phase
systems.

Common structure in both tissue-based and formulated
foods

Question 2

Are dispersions stable or unstable?

Answer 2

Dispersions are physically unstable – kinetic phenomenon

Question 3

what food has different properties when mixed with air compared to just being frozen?

Answer 3

The properties of ice cream are very different compared to the ice cream mix, air and the molten ice cream.

Question 4

give Examples of colloidal dispersions

Answer 4

beer foam, bread, ketchup, mayo, chocolate, butter

Question 5

what is a gas in a liquid called

Answer 5

foam, eg beer foam

Question 6

what is a liquid in a liquid called?

Answer 6

Emulsion
(e.g. Mayonnaise)

Question 7

what is a solid in a liquid called?

Answer 7

Suspension
(e.g. Toamato Ketchup)

Question 8

what is a gas in a solid called?

Answer 8

Solid foam
(e.g.Bread)

Question 9

what is a liquid in a solid called?

Answer 9

Solid emulsion
(eg Butter)

Question 10

what is a solid in a soliod called?

Answer 10

Solid suspension
(Chocolate bars)

Question 11

What characterizes a dispersion?

Answer 11

-Properties of continuous phase
- Properties of dispersed phase
-Properties of interface
- Volume fractions of dispersed phase

Question 12

name Properties of the continuous phase

Answer 12

-Rheology
-Ionic strength
-Thermal properties etc

Question 13

name the Properties of dispersed phase

Answer 13

• Solubility in continuous phase
• Size of droplets/bubbles/particles
• Thermal properties etc

Question 14

what are the Properties of interface?

Answer 14

• Surface tension
• Surface rheology
• Stabilizing molecules

Question 15

what are some Structural elements in dispersions?

Answer 15

-gas bubble
-emulsion droplets
-polymer molecule
-solid particles (amorphous)
-oil droplet with fat crystals
-crystal
-floc or aggregate of particles
-fibers

Question 16

which foods are have very complex structures?

Answer 16

tissue-based foods, eg an apple

Question 17

what else is important in dispersions?

Answer 17

Size and polydispersity is important
in dispersions

Question 17

what are two methos used for Determination of size distributions?

Answer 17

Microscopy
Light Scattering/Diffraction

Question 18

describe the Microscopy method

Answer 18

-Divide at least 200 particles into size classes
-Slow
-Easy to distinguish aggregates
- provides Shape information
-The Bergenståhl rule-of-thumb rapid method

Question 19

descibe the Light Scattering/Diffraction method

Answer 19

-Fast
-“Black box” measurement in many cases
- Does not distiguish aggregates
-No shape info
-Unreliable data when high polydispersity
-Refractive index

Question 20

do Colloidal dispersions have a large surface area?

Answer 20

yes!
Example: Homogenized milk (oil-in-water emulsion, containing 3% fat in
droplets with d approx. 1μm) has a surface area of 180 m 2/L milk

Question 21

what are some Instability problems in colloidal dispersions

Answer 21

-Sedimentation/Creaming
-Flocculation (aggregation)
Flocculation is influenced by surface properties!

Stability is a kinetic phenomenon!

Question 22

what does the size of the particles influence?

Answer 22

-Influences sensory properties – ice crystals, sandyness etc.
-Influences colloidal stability

Question 23

what does Stokes law describe?

Answer 23

sedimentation and creaming
The volume fraction of disperse phase has a huge
influence on sedimentation/creaming!

Question 24

what characterizes Surface active molecules?

Answer 24

*has Hydrophobic and hydrophilic parts * Hydrophobic parts are excluded by water * Can be small or large molecules * In principle all proteins are surface active. * Often referred to as emulsifiers

Question 25

give Examples of low molar mass emulsifiers

Answer 25

-Phsopholipids -Mono- and Diglycerides -Monoglyceride esters of citric or tartaric acid (DATEM and CITREM) -Sodium stearoyl lactylat

Question 26

what can emulsifiers do in aqeous environments

Answer 26

self assemble!

Question 27

name some food emulsifiers

Answer 27

1.Macromolecules -Proteins (Contain both hydrophilic and hydrophobic amino acids) 2.Polysaccharides Naturally surface active (unusual!): Gum Arabic and other exudate gums. 3.Hydrophobically modified polysaccharides.

Question 28

what do Surface active molecules do?

Answer 28

they adsorb at interfaces, ex: Oil-Water Air-Water Solid-Water (depending on interface properties) An adsorbed layer of molecules is created.

Question 29

what are emulsifiers used for?

Answer 29

Mixing of two liquids with low solubility, Addition of emulsifier is for stabilization.

Question 30

which phase is the emulsifier more soluble in?

Answer 30

The phase in which an emulsifier is more soluble constitutes the continuous phase

Question 31

Consider a low-fat spread, an emulsion with volume fraction oil = volume fraction water. How can you find out which is the continuous phase?

Answer 31

If the continuous phase is oil, then adding more oil (the non-polar solvent) will further dilute the sample without causing phase separation. However, if the continuous phase is water, then adding oil will cause phase separation, with the oil forming distinct droplets in the water. Conversely, if you add water to the sample and observe that it readily mixes without phase separation, then the continuous phase is water. However, if adding water causes phase separation, with water droplets forming in the oil, then the continuous phase is oil.

Question 32

what are the five basic mechanisms by which emulsions destabilize?

Answer 32

-gravitational separation/shaking -flocculation -coalescence -oswald ripening/disproportionation -phase inversion

Question 33

what 3 different types of foams are there?

Answer 33

1.gas dispersion 2.transient foams 3.stable foams

Question 34

what does The viscosity of the continuous phase play an important role for?

Answer 34

stability

Question 35

what 3 different mechanisms affect the stability of foam?

Answer 35

1. drainage (gravity driven)/evaporation of continuous phase 2.coalescence (film rupture) 3.disproportionation (oswald ripening)