Factors Affecting Food Emulsion Properties -...
Transcript of Factors Affecting Food Emulsion Properties -...
Factors Affecting Food
Emulsion Properties
D. Julian McClements
Department of Food Science
University of Massachusetts , Amherst
Emulsion Properties Depend on
Droplet Characteristics
• Fat droplets affect:
– Appearance
– Flavor
– Texture
– Shelf-life
Need to Understand Role of Fat Droplets !
Emulsion Appearance
• Product Desirability
• Perceived Product Quality
• Consumer Sensory Expectations
Optical Properties Determine:
Influence of Fat Droplets on
Emulsion Appearance
Incident Wave, I(λ)
Reflected Wave, R(λ)• Absorption
• Scattering
Transmitted
Wave, T(λ)
Hexadecane oil-in-water emulsions (d = 0.3 µm, red dye = 0.1%)
Emulsion Appearance:Effect of Droplet Concentration
Emulsion Appearance:Effect of Droplet Concentration
40
60
80
100
0 5 10 15 20 25
Droplet Concentration
(wt%)
L
0
10
20
30
40
50
0 5 10 15 20 25
Droplet Concentration
(wt%)c
Hexadecane oil-in-water emulsions (d = 0.3 µm, red dye = 0.1%)
Lightness Color Intensity
Fading
Emulsion Appearance:Influence of Titanium Dioxide
40
50
60
70
80
90
0 5 10 15 20 25
Droplet Concentration (wt%)
L
0%0.04%0.10%0.30%
Hexadecane oil-in-water emulsions
(d = 0.3 µm, red dye = 0.1%)TiO2
• Emulsion opacity can be increased by incorporating particles
that effectively scatter light, but are legally acceptable, relatively
inexpensive and compatible with the product
Emulsion Appearance:Effect of Droplet Size
25
30
35
40
45
50
0 10 20 30
Droplet Diameter (µµµµm)
C
Hexadecane oil-in-water emulsions (φ = 10%, red dye = 0.1%)
50
60
70
80
0 10 20 30
Droplet Diameter (µµµµm)
L
Lightness Color Intensity
Emulsion Appearance:Effect of Refractive Index
nd/n
aq= 1
Hexadecane oil-in-water emulsions (φ = 4 wt%, d = 1 µm, 0.002% Red Dye)
Important for high sugar or polyol foods, or for analysis
Main Factors Affecting Emulsion
Appearance
• Droplet Size & Concentration
• Relative Refractive Index
• Dye Type & Concentration
Theoretical models available to
predict emulsion color
Emulsion Flavor
• Product Desirability
• Perceived Product Quality
Flavor Determines:
• Aroma
• Taste
• Mouthfeel
Flavor is:
Reduced Fat Products
Factors Affecting Flavor
• Composition
– Type and concentration of
flavor molecules present
– Food matrix
• Flavor Distribution
– Partitioning of flavors between
different environments
• Molecular Transport
– Molecular transport of flavors
between different environments
Flavor Distribution
Dispersed Phase
Continuous Phase
Interfacial Phase
Flavor Modifiers
Head-space Phase
Partition Coefficient
KHE = cH / cE
Flavor DistributionInfluence of Fat Content
0
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
Fat Content (%)
Head
Sp
ace C
on
c (
10
-4)
Non-polar
Polar
• Initial flavor intensity of emulsions with fixed flavor
content is strongly dependent on fat content
Flavor type:
Molecular Transport Kinetics
�Equilibrium: Partition coefficients
�Kinetic: Molecular transport
Dilution in
Mouth
Taste &
Mouthfeel
Aroma
Volatiles
Non-
Volatiles
Molecular Transport Kinetics
Influence of Fat Content
0
20
40
60
80
0 20 40 60
Time (s)
Fla
vor I
nte
snit
y
0%
1%
5%
15%
30%
• Headspace flavor intensity versus time profile is strongly
dependent on fat content
Malone et al (2000)
Control of Molecular Transport:Encapsulation Technology
• Release rate can be controlled by creation of novel microstructures
Faster Slower
Gelled
Particles
Multiple
Interfacial
Layers
Complexity of Flavor Perception
Factors Influencing Flavor
• Dilution with Saliva
• Change in pH, I, T
• Mixing & Fragmentation
• Swallowing/Breathing
• Transport to Receptors
• Interaction with biological surfaces
Appreciable progress has been made – but more applied and
fundamental research is still required.
Factors Influencing Emulsion
Flavor
• Flavor concentration profile
• Food matrix composition
• Food microstructure
On-line flavor analysis
Rapid progress has recently
been made in understanding
food matrix effects on flavor
Emulsion Rheology
Emulsion Rheology Influences:
Processing operations
– Flow through pipe, stirring, homogenization
Quality attributes
– Texture: “spreability”, “pourability”
– Shelf life: creaming, sedimentation
Sensory attributes
– Mouthfeel: “creaminess”, “smoothness”
Understanding Emulsion Rheology
Mathematical Modeling
Droplet Droplet
characteristicscharacteristics
Continuous phaseContinuous phase
characteristicscharacteristics EmulsionEmulsion
RheologyRheologyMathematicalMathematical
ModelModel
Concentration, size,
interactions
Viscosity,
gel strength
Viscosity,
gel strength
Emulsion RheologyInfluence of Droplets on Viscosity
• Emulsion Droplets Increase Fluid Viscosity
No Particle
Isolated Rigid
Spherical Particle
Greater
Energy
Dissipation(Einstein Equation)
Fluid
Friction
Losses
Greater
Energy
Dissipation
Interacting Rigid
Spherical Particles(DK Equation)
0
10
20
30
40
50
0 10 20 30 40 50 60
φ φ φ φ (wt%)
η/η
η/η
η/η
η/η
00 00 (
Pa
s)
Einstein & DK
Models
DK
Model
Einstein
Model
Emulsion RheologyModeling Influence of Fat Content
Doughery-Krieger
Equation:
ηη = = ηη00(1 + 2.5(1 + 2.5φφ))
Einstein Equation:
ηη = = ηη00(1 (1 -- φφ//φφcc))--[η]φ[η]φcc
• Continuous phase rheology (η0)
• Particle concentration (φ)
• Close packing concentration (φc)
φφφφc
Emulsion RheologyInfluence of Droplets on Viscosity
φφφφ0% 100%
φC
Dilute Concentrated
FLUID-LIKE SOLID-LIKE
Sk
im M
ilk
Hea
vy
Crea
m
May
on
naise
Milk
Infa
nt F
orm
ula
Bev
erage
Lig
ht C
ream
Dressin
g (R
egu
lar)
Dressin
g (L
igh
t)
20% 40% 60% 80%
0
0.005
0.01
0.015
0.02
0.025
0.1 1 10 100
Normalized Shear Stress
η
η
η
η (
Pa
s) 21%
33%
40%
Factors Affecting RheologyFat Content & Shear Stress
Shear
Random
(Low shear)
Ordered
(High shear)
Less frictional losses
0
10
20
30
40
50
0 10 20 30 40 50 60
φ φ φ φ (wt%)
η/η
η/η
η/η
η/η
11 11 (
Pa
s)
High Shear
Limit
Low Shear
Limit
Factors Affecting RheologyFat Content and Shear Stress
ηη = = ηη00(1 (1 -- φφ//φφcc))--[η]φ[η]φcc
It is important to specify & control measurement stress
Note: Small change in φ
gives large change in η
Factors Affecting RheologyDroplet Concentration
0.001
0.01
0.1
1
10
100
1000
0 20 40 60 80
Droplet Concentration (wt%)
Sh
ear
Mo
du
lus (
kP
a)
• Emulsions have solid-like behavior at high droplet concentrations
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80
Droplet Concentration (wt%)P
ha
se
An
gle
(º)
Solid-likeLiquid-like
Factors Affecting RheologyDroplet Size
0
0.5
1
1.5
2
2.5
3
97 91 89 84 80 78 76
Droplet Radius (nm)
Sh
ear
Mo
du
lus (
kP
a)
0
10
20
30
40
50
60
70
80
90
Ph
ase A
ng
le (
º)
Emulsions can exhibit solid-like behavior below critical droplet size, if there are
strong repulsive interactions
LiquidSolid
Factors Affecting RheologyFlocculation
0
5
10
15
20
0 0.2 0.4 0.6
Volume Fraction
Rel
ati
ve
Vis
cosi
ty
Non-Floc
Floc
Hexadecane Oil-in-Water Emulsions, d = 0.53 µm (SDS)
Factors Affecting RheologyModeling Flocculated Emulsion Rheology
3
3
4flocfloc rV π=
droplets
floc
VV
VR =
Non-Flocculated
ηη = = ηη00(1 + 2.5(1 + 2.5φφRRVV))
Modified Einstein
Equation:
3
3
4dropletsdroplets rNV π=
Flocculated
Flocs trap continuous
phase, which
increases their
effective volume
Factors Affecting RheologyFlocculation
0.001
0.01
0.1
1
10
0 20 40 60 80
φφφφ
G*
(P
a)
NF
F
Hexadecane Oil-in-Water Emulsions, d = 0.53 µm (SDS)
Factors Affecting RheologyFlocculation: Shear Thinning Behavior
2
0 //
/1)(
+
+=
∞
∞
i
i
ττηη
ττητη
+=
kT
U
r
kTi
min
31τ
1
10
100
0.01 0.1 1 10 100
Shear Stress (Pa)
ηη ηη/
Pa
s
Flow field
Deformation
Partial
disruption
Complete
disruption
Major Factors Affecting
Emulsion Rheology
ηη = = ηη00(1 + 2.5(1 + 2.5φφeffeff + 6.2+ 6.2φφeff eff +...)+...)
• Continuous phase rheology (h0)
• Particle concentration (φ)
• Particle interactions (w(h))
• Particle size (r)
• Applied shear stress (G)
φφeffeff = = ff((φφ, , ww((hh), ), rr, , GG))
φφeffeff
Influence of Fat Droplets on
Emulsion Mouthfeel
How do fat droplets
interact with tongue
surface ?
Bulk Rheology
or
Specific Interactions?
Thin Film Rheology - Tribiology
Emulsion Properties Depend on
Droplet Characteristics
• Fat droplets affect:
– Appearance
– Flavor
– Texture
– Shelf-life
Need to Understand Role of Fat Droplets !