double emulsions: fundamentals and opportunities · double emulsions: fundamentals and...

Flanders’ FOOD Technology day 2010

Double emulsions: Fundamentals

and opportunitiesDr Bettina Wolf

[email protected]

Associate Professor in Biomaterials Science

Division of Food Sciences

The University of Nottingham, UK

Food emulsions

2


Covered in this lecture

• Emulsion structures

• Double emulsions

– Applications

– Issues

– Formulation

• Textbook references

3

Mixing oil and water

4

www.simscience.org/membranes/advanced/page3.html


Stabilised droplets

5

oilemulsifier molecule

water

oil-in-water emulsion(o/w emulsion)

Emulsion microstructures

• Single emulsions

• Double emulsions (multiple emulsions, duplex

emulsions)

• Submicron emulsions

• Biliquid foams / high internal phase emulsions

(HIPE)

6


Single emulsions

7

o

w

oil-in-water (o/w)

w o

water-in-oil (w/o)

o w

(macro) emulsion or simple emulsion

• thermodynamically unstable, but…

• kinetic stable system

• droplet sizes (0.1) 1…100 µm

mini emulsion or submicron emulsion:

• droplet sizes 100 nm …1 µm

• nano emulsion: droplet sizes < 100 nm

micro emulsion

• thermodynamically stable system through

very low interfacial tension < 10-3 mN/m

• self forming upon mixing of ingredients

• droplet sizes well < 100 nm

• up to 30 % of surfactants & co-surfactants

required

Double emulsions

8

oil-in-water (o/w)

w o

(o/w)-in-oil (o/w/o)

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

o w


Micrographs

9

25 µm

o/w

100 µm

w/o/w

Meyer T, Akimov D, Tarcea N, Chatzipapadopoulos,

Muschiolik G, Kobow J, Schmitt M, Popp J (2008) J.

Phys. Chem. B 122, 1420-1426.

w/o/w

10 µm

Monodisperse emulsionsAdvanced manufacture: microfluidics

10

200 µmPictures from the Webpage of the Experimental Soft

Condensed Matter Group at Harvard University, Prof DA Weitz

Whitesides GM (2006)

Nature 442, 368-373.

Flow-focussing system


Monodisperse emulsionsAdvanced manufacture: membrane emulsification.

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Sketch and data courtesy of F.

Spyropoulos, University of

Birmingham, UK.

oil

water

200 µm

o/w

Sintered porous glass membranes.

Left: 2.8 µm membrane.

Right: 7 µm membrane.

w/o/w w/o/w

Microstructure & flow characteristics

12Ribeiro HS, Cruz RCD (2004) Chemie

Ingenieur Technik 75(4), 443-447.

Mason TG (1999) Current Opinion in Colloid & Interface Science 4, 231-238.


Emulsion stability

13

o

w

w o

coalescence

Ostwald ripeningphase inversion

flocculation/aggregation

Breaking -

phase

separation

sedimentation/creaming

v ∝ xdroplet2

pcap ∝ x-1

Emulsifiers

14

molecular

(surfactant)1

particulate

small molecular

polymeric

monoglycerides, lecithins,

glycolipids, fatty alcohols,

fatty acids…

Oil soluble: ethylcellulose2,3

Water soluble: proteins,

polysaccharides (gum arabic,

methylcellulose4)

fat crystal network1,5

lipophilichydrophilic

1Kravola & Sjöblom (2009) Journal of Dispersion Science and Technology 30, 1363-1383.2Melzer et al (2003) European Journal of Pharmaceutics and Biopharmaceutics 56(1) 23-27. 3Do et al (2010) Reactive & Functional Polymers article in press.4Floury et al (2003) Journal of Food Engineering 58(3) 227-238.5Rousseau (2000) Food Research International 33, 1-14.

1

microbial1


15

Particulate emulsifiers

16

Hunter TN et al (2008) Advances in Colloid and Interface Science 137, 57-81.


Particles at interfaces

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1µm

Oil-in-water emulsion stabilised

with 200nm silica particles.

1µm

Oil-in-water emulsion stabilised with

partially hydrophobised 500nm silica

particles. Scarce surface coverage as

also observed by others1,2.

1 Binks BP et al (2005) Langmuir 21, 8161.

2Vignati E & Piazza R (2003) Langmuir19, 6650.

Food examples

18

Fat globule stabilised air

bubble of a whipped cream

Water (30%) in cocoa butter emulsion

10 µm

Double emulsion with inner interface fat

crystal stabilised

No

rto

n J

E &

No

rto

n I

T (

20

10

) S

oft

Ma

tte

r 6

, 3

73

5-3

74

2.

25 µm

Cellulose micro-rods for foam stabilisation.

Campbell AL et al (2009) Soft Matter 5, 1019-1023.


Applications for double emulsions

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• Encapsulation

– Flavour

– High value ingredients/nutrients

– Masking

• Partial fat reduction

• Salt reduction

Partial fat reduction

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• Savoury sauces and dressings

• Spreads

• Chocolate and confectionary

See contribution

by Philip Cox (TP2)


Salt reduction

21

w/o/w w/o/w+

o/w o/w+

+ indicates presence of pea purée

‘more texture’ enabling sensory analysis for salt perception2

Hypothesis:

Concentrating salt in external product phase increases salt perception1.

1Morris et al (2009) Chemosensory Perception 2(1) 1-8.2Lad et al (unpublished data)

Salt reduction

22Lad et al (unpublished data)

water

fluid

samples

thickened

samples

� Hypothesis was successfully tested.


Issues with double emulsions

23

“To date, there are no products on the market that contain

double emulsions, because they are difficult to keep stable

and also to manufacture in volume. Part of the problem is that when a

double emulsion containing water has sugar or salt in one of the other phases, the

combination creates osmotic pressure. This means that the water migrates towards the

more salty or sugary side of any interface, and so the emulsion breaks down.”

Me

zze

ng

a e

t a

l (2

00

4)

Lan

gm

uir

20

, 3

57

4-3

58

2.

Difference in chemical

potential between water

compartments rather than

unbalanced osmotic

pressures can be reason for

instability.

Pawlik et al (unpublished data)

Stable double emulsions

• Particle stabilisation.

• Gelation of the internal phase.

• Strong elastic external interface through

appropriate structuring based on PGPR.

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Textbooks

• Encyclopedic Handbook of Emulsion

Technology by Johan Sjoblom

• Emulsions and Emulsion Stability: 132

(Surfactant Science) by Johan Sjoblom

• Food Emulsions: Principles, Practices, and

Techniques by David Julian McClements

• Encyclopedia of Emulsion Technology: Basic

Theory: 001 by Paul Becher

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