Dispersion Systems Flashcards
Define a dispersion system.
A system in which particles are dispersed in a continuous phase of a different matter
Define true solutions.
- Small molecules or ions, such as sugar, salt, and vitamins dispersed homogenously in true solutions in food
- Very well mixed
Define colloid dispersions.
- Larger molecules such as proteins, pectic substances, cellulose and cooked starch are colloidaly dispersed
- Seemingly mixed
- They can all be separated out
Define suspensions.
- Large fat globules and uncooked starch granules form suspensions
- Readily separate from the dispersion medium upon standing
Provide true solutions examples.
- honey
- sugar in water
- vitamins in water
Provide colloid dispersion example.
- gas in liquid: whipped cream
- liquid in solid: gummy bears
- liquid in liquid: homogenizing milk, cellulose, cooked starch
Provide suspension examples.
- Flour in Water
- Vinegar in Oil
How large are the dispersed medium in true solutions, colloids and suspensions?
True solutions: under 1 nanometer
Colloids: 1 nanometer to 0.2 micrometer
Suspensions: > 0.2 micrometer
If the dispersed medium is gas, and the dispersion medium is liquid, what is the type of dispersion?
Foam
If the dispersed medium is gas, and the dispersion medium is solid, what is the type of dispersion?
Solid foam
If the dispersed medium is liquid, and the dispersion medium is liquid, what is the type of dispersion?
Emulsion
If the dispersed medium is liquid, and the dispersion medium is solid, what is the type of dispersion?
Solid Emulsion or gel
If the dispersed medium is solid, and the dispersion medium is liquid, what is the type of dispersion?
Suspension
Name 3 ways you can change the degree of dispersion.
- Heat
- Mechanical Treatment
- Adding Acid
Is heating a sugar solution, a gelatin gel, and egg whites reversible?
- Sugar and gelatin geel: reversible
Egg whites: irreversible
Does heating a sugar solution, a gelatin gel, and egg whites increase or decrease the degree of dispersion?
- Sugar and gelatin geel: increase
Egg whites: decrease
How does raw egg white change with heat?
1) Folded proteins (raw) - hydrophilic –> denature
2) Unfolded proteins (hydrophilic and hydrophobic) –> aggregate
3) Aggregated proteins (cooked) - hydrophilic and hydrophobic
Name 3 kinds of mechanical treatment.
- Beating egg whites
- Grinding meat
- Homogenization of milk
Does mechanical treatment of beating egg whites, grinding meat, and homogenizing milk increase the degree of dispersion? What coagulates/disperses?
Egg whites: decreases, protein coagulation
Grinding meat: increases, dispersion of connective tissue
Homogenization of milk: increases, dispersion of fat globules
If you add an acid to milk and the pH decreases below 4.6, what will happen? Will that increase of decrease the degree of dispersion?
- Casein particles will coagulate and separate from whey
- Decrease degree of casein dispersion
What is an example of a colloid?
Homogenized milk (butter fat globules dispersed through a water solution)
Arrange the dispersion systems in order of least stable to most stable.
Least: suspensions, colloids, solutions: Most
What are the main 3 factors responsible for the stabilization of colloidal systems?
- Brownian movement of the dispersed particles
- Like Electric charges of the dispersed particles
- Water of hydration around the dispersed particles
What is the brownian movement?
Continuous movement of colloid particles due to bombardment from dispersion medium molecules
- Improves colloid stability (can’t set since they’re zig zagging)
What would result in a greater dispersion due to more movement of colloid particles?
Smaller colloid particles + less viscous dispersion medium
How does the brownian movement change with temperature?
Increases with temperature
Do repulsive or attractive forces improve colloid stability? What would disrupt?
- Repulsive forces improve stability (like charges)
- Addition of acid or base disturbs the charges on the colloid molecules: acid coagulation of milk proteins
If the dispersed medium is hydrophilic, how will that affect stability? What will you need to add?
- Decrease stability, will separate out (non-homogenized milk)
- Need to add an emulsifying agent
What is an emulsion? What does it require?
A mix of 2 or more liquids that are normally immiscible (non-mixable)
Requires an emulsifier
What are the 3 phases in an emulsion?
- The dispersed (discontinuous)
- The dispersion (continuous)
- The emulsifier (stabilizer)
Name some common emulsifiers.
Lecithin Milk proteins Soy proteins Gelatin Gluten Vegetable gums Starches Ground paprika Dry mustard
What are the two types of emulsions?
- Oil in water: oil is dispersed, water is dispersion
- Water in oil: water is dispersed, oil is dispersion
What is a foam?
Agglomeration of gas bubbles separated from each other by thin films (liquid or solid)
What are liquid foams? Give examples.
- Gas in liquid dispersion
- Whipped cream, whipped egg whites, draft beer foam, mousse
What are solid foams? Give examples.
- Gas in solid dispersion
- Sponge toffee, bread, marshmallows, aero
What is gelatin?
Proteins extracted from collagen, hides, and connective tissues of animals
What is a sol? What is the dispersed and the dispersion medium?
- a dispersion of solid colloidal particles in a liquid dispersion medium
Are sols pourable, can they gel?
- Pourable
- Gel transformations can occur under appropriate conditions
What is a gel? How many phases are there? How can it be made firmer?
- 2 phase system
- High degree of interface between the continuous phase (solid) and the dispersed phase (liquid) = firmer gel
How is gelatin prepared?
Protein separate out, line up, break up into strands, curl up again, join up with other strands, make an unbreakable irreversible matrix.
What effects gelation?
- Gelatin concentration
- Temperature
- Sugar
- Acid
- Enzymes
- Salts
- Solid ingredients
