Advanced food physics lectures
Inhoud
2. Rheology of soft solids........................................................................................................................4
3. Fracture behaviour of soft solids......................................................................................................11
4. Texture perception...........................................................................................................................12
5. Soft Solids part – Microstructure of soft foods.................................................................................12
b. Plastic fats.....................................................................................................................................15
c. Closed packed systems.................................................................................................................16
1. Emulsions..........................................................................................................................................21
2. Interfacial phenomena:....................................................................................................................22
3. Role of surfactants............................................................................................................................23
4. Pickering emulsions..........................................................................................................................27
5. Preparing emulsions.........................................................................................................................29
6. Stability of emulsions........................................................................................................................31
7. Properties of emulsions....................................................................................................................33
1
,2
,Introduction
General theme of this course: Examine the link between structure of a food product and its
physical properties
Structure has a large influence on the properties of a food product
- Mechanical properties
- Physical stability
- (flavour) release
Most foods are dispersed systems with a heterogeneous distribution of structure elements
Example structure elements as dispersed phase: Gas bubbles, polymers, solid particles,
crystals, oil or water droplets, fibres (insoluble polysaccharides), protein aggregates.
Classification of food products:
Central questions:
1. How do these structures form? Molecular and colloidal interactions between the various
components and structural elements
2. What is the effect of the microstructure on physical properties? That is the main
question we will address in this class, for a number of specific systems: 1. Soft solid food
products and 2. Emulsions.
Structure of the course:
- Rheology, fracture and structure of soft foods
- Emulsions and surface phenomena
3
, 1. Soft solids Rheology
Definition of a solid: Material with a predominantly elastic response to an applied force
(material can store energy and does not immediately yield) Rheological definition: Tan δ <1.
Modulus E, G<108 Pa. Examples: Bread, cheese, meat, fruit, desserts, mousse, jam, butter,
sausage, chocolate
Classes of soft solids
1. Gels
Polymer gels contain triple helix structures, e.g., Gelatin. Highly elastic.
Particles gels contain network of clusters, e.g., casein micelles.
2. Closely packed systems
Mayonnaises: 60-80% oil droplets in water. Not gelled, but still some elasticity.
3. Cellular materials
Most fruits and vegetables have this type of structure. Mechanical strength determined
by stiffness of matrix --- different from jammed systems (Strength determined by
stiffness particles)
4. Mixed systems: Structures somewhere in between, like ice cream.
2. Rheology of soft solids
1. Importance of rheology (rheology of fluids: Walstra chapter 5 and Coupland chapter 7)
- Production (processing)
- Storage
- Handling
- Consumption
2. Modes of deformation
- Uni-axial compression of compressible material: Apply force on the top and bottom.
Youngs modulus is the stiffness. A= only the top part.
Stress is NOT a scalar: Stresses have a direction! Since we have three coordinates (x,y,z)
we have a total of 9 stress components. Stress is a tensor, and it can be written in a
matrix form. Only six components need to be specified to fix the stress tensor.
Likewise: The deformation or strain (y) is also a tensor:
4
Inhoud
2. Rheology of soft solids........................................................................................................................4
3. Fracture behaviour of soft solids......................................................................................................11
4. Texture perception...........................................................................................................................12
5. Soft Solids part – Microstructure of soft foods.................................................................................12
b. Plastic fats.....................................................................................................................................15
c. Closed packed systems.................................................................................................................16
1. Emulsions..........................................................................................................................................21
2. Interfacial phenomena:....................................................................................................................22
3. Role of surfactants............................................................................................................................23
4. Pickering emulsions..........................................................................................................................27
5. Preparing emulsions.........................................................................................................................29
6. Stability of emulsions........................................................................................................................31
7. Properties of emulsions....................................................................................................................33
1
,2
,Introduction
General theme of this course: Examine the link between structure of a food product and its
physical properties
Structure has a large influence on the properties of a food product
- Mechanical properties
- Physical stability
- (flavour) release
Most foods are dispersed systems with a heterogeneous distribution of structure elements
Example structure elements as dispersed phase: Gas bubbles, polymers, solid particles,
crystals, oil or water droplets, fibres (insoluble polysaccharides), protein aggregates.
Classification of food products:
Central questions:
1. How do these structures form? Molecular and colloidal interactions between the various
components and structural elements
2. What is the effect of the microstructure on physical properties? That is the main
question we will address in this class, for a number of specific systems: 1. Soft solid food
products and 2. Emulsions.
Structure of the course:
- Rheology, fracture and structure of soft foods
- Emulsions and surface phenomena
3
, 1. Soft solids Rheology
Definition of a solid: Material with a predominantly elastic response to an applied force
(material can store energy and does not immediately yield) Rheological definition: Tan δ <1.
Modulus E, G<108 Pa. Examples: Bread, cheese, meat, fruit, desserts, mousse, jam, butter,
sausage, chocolate
Classes of soft solids
1. Gels
Polymer gels contain triple helix structures, e.g., Gelatin. Highly elastic.
Particles gels contain network of clusters, e.g., casein micelles.
2. Closely packed systems
Mayonnaises: 60-80% oil droplets in water. Not gelled, but still some elasticity.
3. Cellular materials
Most fruits and vegetables have this type of structure. Mechanical strength determined
by stiffness of matrix --- different from jammed systems (Strength determined by
stiffness particles)
4. Mixed systems: Structures somewhere in between, like ice cream.
2. Rheology of soft solids
1. Importance of rheology (rheology of fluids: Walstra chapter 5 and Coupland chapter 7)
- Production (processing)
- Storage
- Handling
- Consumption
2. Modes of deformation
- Uni-axial compression of compressible material: Apply force on the top and bottom.
Youngs modulus is the stiffness. A= only the top part.
Stress is NOT a scalar: Stresses have a direction! Since we have three coordinates (x,y,z)
we have a total of 9 stress components. Stress is a tensor, and it can be written in a
matrix form. Only six components need to be specified to fix the stress tensor.
Likewise: The deformation or strain (y) is also a tensor:
4
