Food Emulsion_Stability ppt

“Aggregation due to fusing together of two or more individual droplets to form a bigger droplet”
Droplet Coalescence
Oil
A few nms
Water Oil
Droplet coalescence depends on precise molecular details of droplet interfaces - difficult to predict!
“Oiling Off”:
Solvent Extraction Method
Petroleum ether Emulsion shake
• Measure amount of oil that can be extracted by an organic solvent
“Oiling Off”:
Instrumental Techniques
• Microscopy • Particle Sizing • Creaming stability/Oiling Off
Experimental Protocols
• Storage Tests • Accelerated Storage Tests • Environmental Stress Tests
Evolution of Coalescence
Homogeneous Coalescence
Coalescence rate independent of droplet size
Heterogeneous Coalescence
Coalescence rate increases with droplet size
0 wt% sucrose
20 wt% sucrose
Oil-in-water emulsions stabilized subjected to freeze-drying
Droplet Coalescence: Influence of
Interfacial Membranes
• 1º Highly Unstable • 2º Stable to Coalescence Only • 3º Stable to Coalescence, Flocculation & Creaming
Emulsion to Be Tested
Particle Diameter (µ m)
12 10
Add Deflocculant (e.g., surfactant)
Volume%
0.1 1 10 100
4 3.5 3 2.5 2 1.5 1 0.5 0 0.01 0.1 1 10 100
Volume%
Extensive droplet coalescence can lead to the formation of a thin layer of oil on top of a product (sometimes with little change in PSD of bulk emulsion)
0 -0.05 -10
Fat Crystallization
0 10 20 30 40
0 -0.05 -10
Water & Fat Crystallization
0 10 20 30 40
Heat Flow
-0.1 -0.15 -0.2 -0.25 -0.3
Heat Flow Temperature (ºC)
Centrifuge • Time • Speed
Oil
Cream
Serum
HReleased
HC
P
CR OSM
∆ρg (VTotal − VReleased ) = A
Partial Coalescence
Aggregation Fusion
“Clumping of partially crystalline droplets due to penetration of fat crystal from one droplet into another droplet”
Factors Influencing Droplet Coalescence: Ingredient Interactions
Without chitosan (1-month old emulsion)
0.01 wt. % chitosan (the same magnification)
Factors Influencing Droplet Coalescence: Freezing & Thawing
Partial Coalescence in Ice Cream
Partially coalesced droplets in continuous phase Air bubble Partially coalesced droplets around air bubble
Ice cream viewed by cryo-SEM (Douglas Goff. Guelph)
Methods of Controlling Partial Coalescence
% Coalescence
100 80 60 40 20 0 1º 2º 3º
-10º -40º
Emulsion
3 Cycles: -10ºC/30ºC
Features of Coalescence
35 30 25 20 15 10 5 0
0.1 1
φ (%)
百度文库
0 hours 24 hours
10
100
100
Oiling Off (%)
80 60 40 20 0 -40 -20
Water Crystaln
Fat Crystaln
Tween 20
Casein
0
20
40
Temperature (ºC)
Characterization of Coalescence:
Centrifugation Methods
Particle Size Analysis
14 12
37 0 -20
Volume%
10 8 6 4 2 0 0.01
37 ºC : All liquid -0 ºC: Fat crystallizes -20 ºC: Water crystallizes
1
100
Particle Diameter (µ m)
Stability of Food Emulsions (2)
David Julian McClements Biopolymers and Colloids Laboratory Department of Food Science
Droplet Coalescence
“Oiling Off”
“Coalescence”
Characterization of Coalescence:
Microscopy Methods
Particle Size Distribution, Flocculation vs. Coalescence (Image Analysis Software)
Characterization of Coalescence:
Factors Influencing Droplet Coalescence
• Relative magnitude of forces between droplets • Resistance of interface to disruption • Duration of contact between droplets • Shearing and tearing of interfaces
100 80 60 40 20 0 0 20 40 60 80 100
E C (%)
SFC (%)
Influence of Interfacial Membrane on Partial Coalescence
Oiling Off (%)
Thin Membrane -Prone to PC - e.g., Tween 20
8 6 4 2 0 0.01
Particle Diameter (µ m)
Particle Diameter (µ m)
Initially Flocculated
Initially Coalesced
Measurement of “Oiling Off”
Stable Emulsion Coalescence Oiling Off
-0.1 -0.15 -0.2 -0.25 -0.3
Temperature (ºC)
Fat crystallization behavior of oil-in-water emulsions
Characterization of Coalescence:
Coalescence/Oiling-off by DSC
(2). Increase Repulsion (3). Decrease droplet contact (4). Increase resistance of membrane to rupture
Measurement of Coalescence
Techniques & Protocols
100 80 60 40 20 0 -10 0 10 20
Casein Tween 20
Thick Membrane -Resistant to PC - e.g., casein
Temperature (ºC)
Case Study: Ice Cream Manufacture
Add Surfactant & Age Fat globules covered with thick milk protein membrane Fat globules covered with thin surfactant membrane
0 wt% sucrose
20 wt% sucrose
Hydrogenated palm oil-in-water emulsions stabilized by WPI (-40 ºC/40ºC) – sucrose modifies ice crystal formation
Factors Influencing Droplet Coalescence: Dehydration
Dye Dilution Method
Add Dye
Mix
Centrifuge
Absorbance
Cuvette Emulsion
• Measure dilution of dye solution by free oil
Characterization of Coalescence:
Coalescence/Oiling-off by DSC
SEM Images of Partial Coalescence
40ºC (Liquid droplets)
0ºC (Partially Crystalline Droplets)
O/W Emulsions viewed by SEM (John Coupland, Penn State)
Influence of Droplet SFC on Partial Coalescence
Diameter (µ m)
• Bimodal PSD Evolution • “Oiling off”
Strategies to Reduce Coalescence
Principle (1). Reduce Attraction Method • Avoid depletion • Avoid bridging • Avoid hydrophobicity • Alter pH or I (E/S) • Increase thickness (S) Add thickening or gelling agent Use polymeric emulsifier
Potential Problems: Sampling, Distinguishing from flocculation
Characterization of Coalescence:
Distinguishing from Flocculation
4 3.5 3
Volume%
2.5 2 1.5 1 0.5 0 0.01 0.1 1 10 100