Starch Flashcards
1
Q
What are dispersion systems?
A
- Food mixtures of substances in various molecular states (solid, liquid, gas)
- Dispersed phase (eg. oil)
- Continuous phase (eg. vinegar)
- Dispersed phase is scattered throughout continuous phase
2
Q
How do you classify dispersion systems?
A
- State of matter of two phases (solid, liquid, gas)
- Size of dispersed particles
- True solutions: very small molecules or particles dispersed in a liquid
- Colloidal dispersions: intermediate size particles, but still relatively small
- Suspensions: comparatively large dispersed particles or large groups of molecules
3
Q
What are true solutions?
A
- Small molecules or ions include sugars, salts, and vitamins
- Molecules are in constant kinetic motion
- Homogenous mixture because dispersed phase is evenly distributed throughout continuous phase
- Very stable as dispersed phase does not separate from continuous phase
- Do not form a gel
4
Q
What are colloidal dispersions?
A
- Dispersed particles are macromolecules or groups of smaller molecules such as proteins, pectic substances, and cooked starch
- Have special properties due to size of dispersed particles
- Dispersed particles have less kinetic energy and do not move rapid
5
Q
What are the stabilizing factors for colloidal dispersions?
A
- Brownian movement
- Random movement of colloidally dispersed particles as they are constantly and unevenly bombarded by water molecules
- Constant slow movement in all directions
- Least effective/least important factor - Repelling
- Dispersed particles have the same electrical charge on the surface of every particle, therefore they repel each other
- Colloidally dispersed food particles have negative charges on surface
- Repulsion keeps colloidal particles separate and scattered across the continuous phase - Water of hydration
- Layer of water molecules attached to the surface of colloidally dispersed particles by weak hydrogen bonds
- Moves with colloidal particles
- Forms protective shell around dispersed particles
- Helps prevent contact and bonding between colloidal
6
Q
Can colloidal dispersions form gels?
A
- Under certain circumstances dispersed particles will settle out of colloidal dispersion
- Occurs when dispersed particles bond with each other and form larger sized molecules
- Increase in size makes it difficult for dispersed phase to stay suspended in solution (unstable = settle out of colloidal dispersion)
- Have the unique ability for form a gel and take on the shape of a container
7
Q
What are suspensions?
A
- Include cornstarch granules in cold water or groups of molecules like fat globules or temporary emulsions
- Very unstable as gravity causes dispersed particles to quickly separate from continuous phase upon standing
- Do not form gels
8
Q
What are the sources of starch?
A
- Roots
- Eg. potatoes, arrowroot, tapioca
- Found in plastids in the cytoplasm - Cereal
- Eg. wheat, rice, corn
- Found in endosperm of the grain
9
Q
What is amylose?
A
- Linear chain molecule
- Polymer of glucose
- Actual number of glucose molecules depends on source of starch
- Human body can break down linkages to give us energy
- Cereal starches have higher amylose content than root starches
10
Q
What is amylopectin?
A
- Branched molecule (bushy but compact)
- Polymer of glucose
- Also source of energy
11
Q
What are SOLs?
A
- Dispersed colloidal particles in a continuous liquid medium
- Thickened mixture which can be poured from a container
- Molecules move randomly, can’t tell which is starch and which is water because it is dispersed
- Eg. hot jam or jelly or hot white/béchamel sauce
12
Q
What are GELs?
A
- High degree of attraction between a continuous system of solid material that holds finely dispersed liquid
- 3D, takes on and keeps shape of container
- Eg. cold starch thickened pudding, set fruit jelly
13
Q
How do you get a colloidal mixture from suspension? What are the types?
A
- Raw starch + cold water forms a suspension (large particles, starch falls to bottom)
- Starch cooked in water forms a colloidal dispersion (intermediate size particles) which normally exist as sol (liquid and pourable)
- Can be turned into a gel if colloidally dispersed particles join together to form a continuous network
- Liquid (water) from continuous phase is trapped in network
14
Q
What is gelatinization? What occurs?
A
- From suspension to colloidal dispersion
- Irreversible swelling of starch granules when heated in the process of water
- During heating, kinetic energy of water increases
- Within starch granule, hydrogen bonds between starch molecules is broken (membrane breaks)
- Water moves into the starch granule and they expand in size
- Some amylose molecules diffuse out of granules while amylopectin stays in the granule
- Membrane only allows linear molecules to go through because branched molecules get stuck
- This creates thick but still pourable SOL
Increase in viscosity (thickness) and translucency (clearness)
15
Q
What is retrogradation? What occurs?
A
- Setting of a cooled gelatinized starch sol to form gel
- Cooling means reduction in kinetic energy
- Amylose molecules, which diffused out of granules during gelatinization, form hydrogen bonds with other amylose molecules, surface of swollen starch granules, branches of amylopectin molecules sticking out of granules
