dispersion systems

Question 1

what is a true solution

Answer 1

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

very well mixed
< 1nm
stable

Question 2

what are colloid dispersions

Answer 2

Larger molecules such as proteins, pectic substances, cellulose and cooked starch are colloidaly dispersed

seemingly mixed
not as stable as true solutions
ie. homogenized milk. ilk fat particles are made smaller to disperse into liquid. if not homogenized, fat stays on top of milk

Question 3

what are suspensions

Answer 3

large fat globules and uncooked starch granules

readily separates from dispersion medium

least stable

ie. vinegar in oil
>0.2 micrometer

Question 4

what do:
gas+ liquid form?
gas + solid?
liquid + liquid?
liquid + solid?
solid + liquid?

Answer 4

gas+ liquid form = foam
gas + solid = solid foam
liquid + liquid = emulsion
liquid + solid = gel
solid + liquid = suspension

Question 5

how to change dispersion degree

Answer 5

heat:

• gelatin: breaks H bonds
• egg whites: proteins bond together (irreversible)

mechanical treatment
-beating egg white: protein bonds break, reform, makes matrix

acid:
- milk: H+ causes casein particles to coagulate = separates from whey = curdling

Question 6

what is a colloid

Answer 6

clloid state: between true solution and suspension

colloid: a substance microscopically dispersed throughout another substance
ie. homogenized milk = butter fat globules dispersed through water solution

Question 7

are solutions and suspensions more or less stable than colloids?

Answer 7

solutions more stable

suspensions less stable

Question 8

what are 3 factors that affect colloid stability?

Answer 8

1. brownian movement of particles:
   - continuous mvmt of colloids
   - smaller colloids + less viscous dispersion = more mvmt of colloid = greater dispersion
   - increases with temp
2. like electric charges::
   - repulsive forces = higher stability of colloid systems
   - adding acid/base disturbs charges = coagulation
3. water of hydration
   - hydrophilic: stable
   - hydrophobic: not stable

Question 9

3 phases of emulsions?

Answer 9

1. dispersed (discontinuous)
2. dispersion (continous)
3. emulsifier (stabilizer)

Question 10

types of emulsions

Answer 10

1. oil in water
   - oil: dispersed phase
   - water: dispersion phase
2. water in oil
   - vice versa

Question 11

types of foam

Answer 11

1. liquid foam: gas in liquid dispersion (ie. whipped cream)

2. solid foam: gas in solid dispersion (ie. bread)

Question 12

structure of gels

Answer 12

SOL: dispersion of solid colloidal particles in liquid dispersion

• pourable
• can turn into a gel depending on temp and pH

GEL:

• can’t turn into a sol
• very firm gel matrix