Gelling Mechanisms Flashcards
What type of dispersion is mayonnaise and what are its continuous and dispersed phases?
Emulsion
Continuous = liquid
Dispersed = liquid
What type of dispersion is milk and what are its continuous and dispersed phases?
Sol
Continuous = liquid
Dispersed = solid
What type of dispersion are meringues and what are its continuous and dispersed phases?
Foam
Continuous = liquid
Dispersed = gas
What type of dispersion is bread and what are its continuous and dispersed phases?
Solid foam
Continuous = solid
Dispersed = gas
What is rheology?
The science of deformation and flow behaviour of matter
What is rheology enable us to do?
Assess the texture of foods
Make special products = slow or rapid release gels for drugs
What is viscosity?
Resistance to flow
What is shear stress?
Resistance to an applied force
What is shear rate?
The gradient of velocity in a flowing material
How can viscosity be measured?
Using a capillary viscometer or a rotational viscometer
What is the equation for viscosity?
Shear stress / Rate of shear
What is newtonian flow?
Shear stress is proportional to shear rate
What is psuedoplastic flow?
Viscosity decreases with shear
What is dilatant flow?
Viscosity increases with shear
What is bingham plastic?
A yield stress has to be overcome before the material starts to flow
What is a gel?
Continuous phase of interconnected particles mixed with a continuous liquid phase
When do gels formulate?
On heating and subsequent cooling
How are reversible gels cross-linked?
By noncovalent bonds
- Hydrophobic
- Electrostatic
- Hydrogen
How are non-reversible gels linked?
By covalent bonds
- Disulphide
What are the uses of polysaccharide gels?
In pharmaceutical and cosmetic products
Where do polysaccharide gels come from?
Tress = gums
Seeds
Fruit = pectin
Seaweed = carrageenan
Are polysacchairde gels usually thermo-reversible or thermo-irreversible?
Thermoreversible = melt on heating and set on cooling
What are the properties of gels?
Can be rigid, elastic or brittle depending on the gelling agent
Not stable as they lose water
What are the factors affecting the formation of gels?
Temperature
Chemical alteration of gelling agent
Number of charged groups
Addition of water competitive compounds
