Stability of Food Emulsions (1) - University of Massachusetts Amherst

24 Pages·2008·3 MB·English

Stability of Food Emulsions (1)
David Julian McClements
Biopolymers and Colloids Laboratory
Department of Food Science
Definition and Importance of
Emulsion Stability
Definition: "Ability to resist
changes in properties over
time”
Importance: Determines the
shelf-life and processing of
Arcocolors.com
food emulsions
May be desirable or undesirable
Emulsion Stability:
Kinetic
versus Thermodynamic Stability
Emulsion
Kinetically
Thermodynamically
Stable
Stable
∆G*
Gf
Kinetically
Unstable
Thermodynamically
∆G
Stable
Gi
Separated Phases
Physical stability:
Ability to resist changes in spatial distribution
of ingredients over time
- e.g., creaming, flocculation, coalescence..
Chemical stability:
Ability to resist changes in chemical structure
of ingredients over time
- e.g., ω-3 oxidation, citral degradation
Physical Stability Mechanisms
Stable
Emulsion
Phase
Gravitational Coalescence
Separation
Separation or
Ostwald
Ripening
Flocculation
Importance of Identification of
Major Instability Mechanisms
• Every food emulsion is unique!
• There is no single strategy that can be used to
generally improve food emulsion stability
• It is therefore crucial to identify the major
instability mechanism for the specific food
emulsion of interest
• Knowledge of emulsion science and technology
facilitates problem solving
Emulsion Stability Testing:
Diagnostic Approach
Phase separation
Macroscopic Properties
Oiling off
Rancidity
Characterize product
defect
Creaming
Flocculation Instability Mechanism
Coalescence
Determine instability
Ostwald Ripening
mechanism(s)
Process Physicochemical Origin
Ingredient
Identify physicochemical
Storage
+ +
origin
Ca2+
Solution
Gravitational Separation
Principles
F
V
SSttookkeess LLaaww::
UU == --22rr22((ρρ --ρρ ))gg//99ηη
22 11 11
F
G
MMeetthhooddss ooff RReettaarrddiinngg GGrraavviittaattiioonnaall SSeeppaarraattiioonn::
•• RReedduuccee ddeennssiittyy ddiiffffeerreennccee ((∆∆ρρ))
•• RReedduuccee ddrroopplleett ssiizzee ((rr))
•• IInnccrreeaassee ccoonnttiinnuuoouuss pphhaassee vviissccoossiittyy ((ηη))
11
Gravitational Separation
Influence of Density Difference
0.5
)
1
- 0.3 Density Matching
s
1
-
m
0.1
(

6
0
1 -0.1

x -100 0 100 200

2
r -0.3
/
U
-0.5
-3
Density Difference (kg m )
Sunflower oil-in-water emulsions containing weighting agents:
Ester gum, Damar Gum, SAIB or BVO
Gravitational Separation
Influence of Droplet Size
100
U ∝ r2
80
)
y Without thickening agent,
a
d 60
O/W emulsions are unstable
/
m
m 40 to creaming once r > 0.5 µm.
(

U
20
0
0 0.5 1 1.5 2 2.5 3
r (µµµµm)
Sunflower oil-in-water emulsions