Dispersion Systems

Question 1

Define a dispersion system.

Answer 1

A system in which particles are dispersed in a continuous phase of a different matter

Question 2

Define true solutions.

Answer 2

• Small molecules or ions, such as sugar, salt, and vitamins dispersed homogenously in true solutions in food
• Very well mixed

Question 3

Define colloid dispersions.

Answer 3

• Larger molecules such as proteins, pectic substances, cellulose and cooked starch are colloidaly dispersed
• Seemingly mixed
• They can all be separated out

Question 4

Define suspensions.

Answer 4

• Large fat globules and uncooked starch granules form suspensions
• Readily separate from the dispersion medium upon standing

Question 5

Provide true solutions examples.

Answer 5

• honey
• sugar in water
• vitamins in water

Question 6

Provide colloid dispersion example.

Answer 6

• gas in liquid: whipped cream
• liquid in solid: gummy bears
• liquid in liquid: homogenizing milk, cellulose, cooked starch

Question 7

Provide suspension examples.

Answer 7

• Flour in Water

- Vinegar in Oil

Question 8

How large are the dispersed medium in true solutions, colloids and suspensions?

Answer 8

True solutions: under 1 nanometer
Colloids: 1 nanometer to 0.2 micrometer
Suspensions: > 0.2 micrometer

Question 9

If the dispersed medium is gas, and the dispersion medium is liquid, what is the type of dispersion?

Answer 9

Foam

Question 10

If the dispersed medium is gas, and the dispersion medium is solid, what is the type of dispersion?

Answer 10

Solid foam

Question 11

If the dispersed medium is liquid, and the dispersion medium is liquid, what is the type of dispersion?

Answer 11

Emulsion

Question 12

If the dispersed medium is liquid, and the dispersion medium is solid, what is the type of dispersion?

Answer 12

Solid Emulsion or gel

Question 13

If the dispersed medium is solid, and the dispersion medium is liquid, what is the type of dispersion?

Answer 13

Suspension

Question 14

Name 3 ways you can change the degree of dispersion.

Answer 14

• Heat
• Mechanical Treatment
• Adding Acid

Question 15

Is heating a sugar solution, a gelatin gel, and egg whites reversible?

Answer 15

• Sugar and gelatin geel: reversible

Egg whites: irreversible

Question 16

Does heating a sugar solution, a gelatin gel, and egg whites increase or decrease the degree of dispersion?

Answer 16

• Sugar and gelatin geel: increase

Egg whites: decrease

Question 17

How does raw egg white change with heat?

Answer 17

1) Folded proteins (raw) - hydrophilic –> denature
2) Unfolded proteins (hydrophilic and hydrophobic) –> aggregate
3) Aggregated proteins (cooked) - hydrophilic and hydrophobic

Question 18

Name 3 kinds of mechanical treatment.

Answer 18

• Beating egg whites
• Grinding meat
• Homogenization of milk

Question 19

Does mechanical treatment of beating egg whites, grinding meat, and homogenizing milk increase the degree of dispersion? What coagulates/disperses?

Answer 19

Egg whites: decreases, protein coagulation
Grinding meat: increases, dispersion of connective tissue
Homogenization of milk: increases, dispersion of fat globules

Question 20

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?

Answer 20

• Casein particles will coagulate and separate from whey

- Decrease degree of casein dispersion

Question 21

What is an example of a colloid?

Answer 21

Homogenized milk (butter fat globules dispersed through a water solution)

Question 22

Arrange the dispersion systems in order of least stable to most stable.

Answer 22

Least: suspensions, colloids, solutions: Most

Question 23

What are the main 3 factors responsible for the stabilization of colloidal systems?

Answer 23

• Brownian movement of the dispersed particles
• Like Electric charges of the dispersed particles
• Water of hydration around the dispersed particles

Question 24

What is the brownian movement?

Answer 24

Continuous movement of colloid particles due to bombardment from dispersion medium molecules
- Improves colloid stability (can’t set since they’re zig zagging)

Question 25

What would result in a greater dispersion due to more movement of colloid particles?

Answer 25

Smaller colloid particles + less viscous dispersion medium

Question 26

How does the brownian movement change with temperature?

Answer 26

Increases with temperature

Question 27

Do repulsive or attractive forces improve colloid stability? What would disrupt?

Answer 27

- Repulsive forces improve stability (like charges) | - Addition of acid or base disturbs the charges on the colloid molecules: acid coagulation of milk proteins

Question 28

If the dispersed medium is hydrophilic, how will that affect stability? What will you need to add?

Answer 28

- Decrease stability, will separate out (non-homogenized milk) - Need to add an emulsifying agent

Question 29

What is an emulsion? What does it require?

Answer 29

A mix of 2 or more liquids that are normally immiscible (non-mixable) Requires an emulsifier

Question 30

What are the 3 phases in an emulsion?

Answer 30

1. The dispersed (discontinuous) 2. The dispersion (continuous) 3. The emulsifier (stabilizer)

Question 31

Name some common emulsifiers.

Answer 31

```  Lecithin  Milk proteins  Soy proteins  Gelatin  Gluten  Vegetable gums  Starches  Ground paprika  Dry mustard ```

Question 32

What are the two types of emulsions?

Answer 32

- Oil in water: oil is dispersed, water is dispersion | - Water in oil: water is dispersed, oil is dispersion

Question 33

What is a foam?

Answer 33

Agglomeration of gas bubbles separated from each other by thin films (liquid or solid)

Question 34

What are liquid foams? Give examples.

Answer 34

- Gas in liquid dispersion | - Whipped cream, whipped egg whites, draft beer foam, mousse

Question 35

What are solid foams? Give examples.

Answer 35

- Gas in solid dispersion | - Sponge toffee, bread, marshmallows, aero

Question 36

What is gelatin?

Answer 36

Proteins extracted from collagen, hides, and connective tissues of animals

Question 37

What is a sol? What is the dispersed and the dispersion medium?

Answer 37

- a dispersion of solid colloidal particles in a liquid dispersion medium

Question 38

Are sols pourable, can they gel?

Answer 38

- Pourable | - Gel transformations can occur under appropriate conditions

Question 39

What is a gel? How many phases are there? How can it be made firmer?

Answer 39

- 2 phase system | - High degree of interface between the continuous phase (solid) and the dispersed phase (liquid) = firmer gel

Question 40

How is gelatin prepared?

Answer 40

Protein separate out, line up, break up into strands, curl up again, join up with other strands, make an unbreakable irreversible matrix.

Question 41

What effects gelation?

Answer 41

- Gelatin concentration - Temperature - Sugar - Acid - Enzymes - Salts - Solid ingredients