double emulsions: fundamentals and opportunities · double emulsions: fundamentals and...
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Flanders’ FOOD Technology day 2010
Double emulsions: Fundamentals
and opportunitiesDr Bettina Wolf
Bettina.Wolf@nottingham.ac.uk
Associate Professor in Biomaterials Science
Division of Food Sciences
The University of Nottingham, UK
Food emulsions
2
Flanders’ FOOD Technology day 2010
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
Flanders’ FOOD Technology day 2010
Stabilised droplets
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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)
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Single emulsions
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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
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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
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Micrographs
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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
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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.
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Emulsion stability
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o
w
w o
coalescence
Ostwald ripeningphase inversion
flocculation/aggregation
Breaking -
phase
separation
sedimentation/creaming
v ∝ xdroplet2
pcap ∝ x-1
Emulsifiers
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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
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Particulate emulsifiers
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Hunter TN et al (2008) Advances in Colloid and Interface Science 137, 57-81.
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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
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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.
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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)
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Salt reduction
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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.
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Issues with double emulsions
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“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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