EXAM 2: Dispersions And Gelatin Flashcards
What is the definition of dispersion ?
A mixture containing particles dispersed in a continuous phase
What can the dispersed phased particles be in the form of
Can be in the form of a gas, solid or liquid
What are the particulars typically in a continuous phase
Solid or liquid
What are the three types of dispersions
True solution, Colloidial dispersion, and coarse dispersion
What is the particle size for true solutions
<1 nanometer
It is a homogeneous solution
What is the particle size for colloidial dispersions
2 nanometers to 1 micrometer
It is between homogeneous and heterogeneous
What is the particle size for a coarse dispersion
> 1 micrometer
It is heterogeneous
What are true solutions
A solute that is equally dispersed in a solvent
The solute does not “settle” out over time
Solutes have different levels of saturation
- unsaturated, saturated or super saturated
Solubility of a substance equals…
Amount in grams that will dissolve in 100 mL of solvent
Saturation of a solution depends on…
Temperature
Starts as unsaturated -> increase temperature -> becomes saturated -> increase temperature
Look at drawing
What is a colloidal dispersion
Two-phase system contains at least one colloid
Colloid = a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance
What are the four types of colloidal systems
Sol, gel, emulsion, and foam
What is the dispersed phased, continuous phase and example of a sol
DP: Solid
CP: Liquid
Ex: Stock, Gravy
What is the dispersed phased, continuous phase and example of a gel
DP: Liquid
CP: Solid
Ex: Gelatin, custard
What is the dispersed phased, continuous phase and example of an emulsion
DP: Liquid
CP: Liquid
Ex: Vinaigrette, mayo, milk
What is the dispersed phased, continuous phase and example of a foam
DP: gas
CP: liquid or solid
Ex: meringue, whipped cream
What is the chemistry of a sol
“Flowing state”
Protein particles are dispersed in soils because of electrical charges on the external surface that cause them to repel each other
Pectins and starches are hydrophilic. Hydrogen bonds in water bind to pectins and starches to keep the starch molecules from binding to one another
What is the chemistry of Gels
Solid particles being to join with one another and decrease the flow of water to form a semi-solid or solid gel (holds shape)
- Proteins: Ionic charges between protein molecules weaken and the protein strands join together
- Starches: lowered energy hydrogen-hydrogen bonds form between starches
- hydrogen in water forms bonds with the solid and become bound to the solid
- remaining water becomes trapped in networks formed by the solid particle
- when gel is cut, the water will be released from the gel “syneresis”
Ingredients/foods that can be in the form of a sol or gel - Proteins
Found in Eggs
- Custard
- Cream/custard pies
Found in Collagen
- Gelatin
- Stocks/meat and poultry juice
Ingredients/foods that can be found in the form of a sol or gel - Carbohydrates
Starches (from grains, roots, tubers)
- Thickened sauces
- cream/custard pies
Plant fibers (pectins and gums)
- gels/gelatin
Gelatin is an example of a ______ to ________
Sol to gel
“Gelation”
Facts about Gelatin
Proteins extracted from the collagen found in the hides, bones and connective tissue of animals
Vegetarian options: Pectins from plants
Powder or granular form
What is the process of making Gelatin (Jello)
- Hydration
- the hydration step is used only for unflavored gelatin powder - add the powder to cool water to allow the gelatin to “hydrate”. This prevents the formation of clumps
- Commercially prepared, flavored gelatin does not need this step because it has been acidified to prevent to formation of clumps - Dispersion
- add hot liquid -> add cool liquid - Gelation
- refridgerate
What are factors that speed/firm gel formation
Cooling temperatures
Adding ice during gelation process
What are factors that delay gel formation or weaken the gel
Acids
Enzymes
The third colloidal dispersion, emulsions is covered in the next set of flashcards
What are characteristics of foams
Food foams: dispersing medium is usually a liquid, sometimes, strengthened by a solid or made into a solid by heating
Gas in liquid
- whipped cream
- beaten egg whites
Gas in solid
- marshmallow
How are foams formed
Mechanical energy is required to make a foam
- energy weakens the surface tension of the liquid allowing it to stretch and capture bubbles of gas (air)
- liquids with lower surface tension and low vapor pressure are best
- solids can be used to make foams
What are the best food sources to make foams
Eggs: denatured proteins provide structure and stability to cell walls
- whites form a stiff foam and yolks a weak foam
Cream and concentrated milk products
- fats in heavy cream form a stiff foam
Gelatin form whipped gelatin
