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Manufacture of Food > Emulsions > Flashcards

Emulsions Flashcards

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1
Q

Define: Emulsion

A

Dispersion of two or more immiscible liquids in which one of the other liquids is dispersed in other as small droplets

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2
Q

Define: Foam

A

Air bubbles dispersed in a liquid

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3
Q

How do we classify emulsions

A

Based off their spatial distribution, i.e what’s in what

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4
Q

What does this image depict

A

Oil in water (o/w) e.g. salad dressings

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5
Q

What does this image depict

A

Oil in water in oil (o/w/o)

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6
Q

What does this image depict

A

Water in oil (w/o) e.g. margarines

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7
Q

What does this image depict

A

Water in oil in water (w/o/w)

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8
Q

What are the applications for emulsions

A
  • Fat reduction (water in oil) - Encapsulation
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9
Q

What effects the type of emulsion formed

A
  • Concentration - Type of emulsifier
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10
Q

What is the disperse phase

A

Droplets

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11
Q

What is the continuous phase

A

What the droplets are in

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12
Q

Why are emulsions thermodynamically unstable

A

All emulsions have different levels of stability. this is because we have increased the surface area

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13
Q

Stable emulsion

A

Droplets that don’t change size and are homogeneously dispersed throughout

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14
Q

What defects can occur in an oil in water emulsion

A

Creaming, flocculation, coalescence, phase seperation

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15
Q

What is Ostwald ripening

A

Smaller droplets in solution dissolve and deposit on larger droplets to reach a more thermodynamically stable state where they have a reduces surface area: volume ratio. Irreversible instability. requires the dissolution of the soluble oil phase

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16
Q

What defects can occur in water in oil emulsions

A

Flocculation, coalescence, sedimentation (instead of phase separation due to density difference)

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17
Q

How can we prevent / slow the instability of an emulsion

A
  • Thickeners e.g. xanthan , carrageenan. increases viscosity so the droplets cant flow as much - Decrease droplets size (Stokes law). Smaller droplets will take longer to rise - Change the emulsifier to impact the charge on the droplet - disperse emulsion to prevent Ostwald ripening.
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18
Q

What defects can occur in foams

A
  • Drainage - Ostwald ripening - Coalescence (promoted by Ostwald ripening and film drainage)
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19
Q

How can we prevent / slow the instability of a foam

A
  • Increase the continuous phase viscosity or solidify it - Smaller bubble size - Gas solubility - Choice of surfactant / emulsifier - Very wet / dry limit
20
Q

Name three types of emulsifiers

A
  • Amphiphilic molecules (surfactant) - Polymeric emulsifiers (proteins) - Particulate emulsifiers
21
Q

Describe how an amphiphilic molecule functions as an emulsifier

A

Hydrophilic head binds with water Hydrophobic tail binds with the oil. Surrounds the droplet

22
Q

What occurs when to much emulsifier is added

A

Emulsifier micelle is formed as it is more thermodynamically favourable

23
Q

Name four surfactants

A
  • Mono and diglycerides of fatty acids - Lecithin - Polysorbates - Citric acid esters
24
Q

What is the HLB

A
  • Hydrophobic Lipophilic Balance
25
Q

Why is knowing the HLB important

A
  • Predicts the behaviour of an emulsifier - Helps select an emulsifier appropriate fir intended application - Hydrophobic emulsifiers stabilise w/o emulsions - Hydrophilic emulsifiers stabilise o/w - This is because of the arrangement at the interface
26
Q

zzzzzzz

A

good

27
Q

Why are polymeric emulsifiers better foam stabilisers than small molecule surfactants

A

They are larger molecules so when they dissolve they create a thicker, more viscoelastic solution. This thick interface makes it harder for the bubbles to move therefore increases stability. As a result it can cope with greater changes in the microstructure

28
Q

How to particulate emulsifiers create a more stable emulstion

A

Absorb at the interface forming different structures depending on the type of particle. e.g. fat crystals

29
Q

How does competitive absorption affect a product

A

Competition for the interface which can impact the size and stability of a system and therefore shelf life stability and product quality

30
Q

List pro’s and cons of each of the types of emulsifier

A
  • Surfactants: smaller emulsion droplets formed. Can be less stable - Proteins: larger droplets, more stable - Particles: cannot make particles small enough so we get larger droplets. Therefore more creaming, coalescence, oily mouthfeel. Different flavour profiles due to the way they’re digested.
31
Q

What needs to be considered when selecting an emulsifier

A
  • Microstructure - Stability - Label declaration.
32
Q

Define: Interfacial tension

A

Energy required to increase the size of the interface between two adjacent phases which do not mix completely with each other

33
Q

What are the two main methods of measuring surface tensions

A
  • Optical. - Force tensiometry
34
Q

What in a homogeniser affects the final microstructure

A
  • Type of homogeniser - The flow of fluid - Composition - Emulsifier amount - How much energy we put in
35
Q

What factors need to be considered when considering droplet breakup and microstructure

A
  • Viscosity ratio - Type of homogenizer (this is determined by the material properties) - flow fields e.g. inertia forces and cavitation
36
Q

What equipment can be used to make emulsions and foams

A
  • Rotor-stator. sheer creates smaller droplets. Makes a course emulsion - Ultrasound continuous emulsification - High pressure homogenisation - Membrane emulsification
37
Q

Name the advantages and disadvantages of a rotor-stator

A
  • Simple setup - Low operational cost - All scales - combination of steps, e.g mix pasteurise emulsify and cool - >1micron - Variance in droplet size - Long process time can cause off flavours to be produced
38
Q

Name the advantages and disadvantages of a high pressure homogenisator

A
  • <1 micron - Requires a course emulsion to begin - Can be processed numerous times to reduce the droplet size
39
Q

Explain the energy input vs droplet size balance

A
  • Small droplet size requires high energy input which is expensive. - More energy causes heat generation which can cause undesirable affects
40
Q

How can we measure an emulsion

A
  • Droplet size and size retention. affects creaming and stability - Viscosity - Texture - Zeta potential (measure charge)
41
Q

Give two examples of an oil-in-water emulsion.

A
  1. Cream
  2. Mayonnaise
42
Q

Give two examples of a water-in-oil emulsion.

A
  1. Butter
  2. Margarine
43
Q

Define:

Creaming

A

The upward movement of droplets due to having a lower density than the surrounding liquid.

44
Q

Define:

Sedimentation

A

The downward movement of droplets due to having a higher density than the surrounding liquid.

45
Q

Define:

Flocculation

A

Two or more droplets coming together to form an aggregate in which the droplets retain individual integrity.

46
Q

Define:

Coalescence

A

Two or more droplets come together to form a larger droplet.

47
Q

As the concentration of PGPR increases, the interfacial tension decreases.

Why is there a plateau at 100?

A

At this point, interfacial tension is not reduced any further with increasing amounts of PGPR because the interface is saturated with surfactants.

Manufacture of Food (4 decks)

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