Physical Aspects of Food

1
Physical Aspects of Food

• M. Burns
• FCS 3120

2
The Plan

• Discuss objective lab review
• Lecture
• Assignment of homework

3
The Nature of Food

• Chemical vs physical properties
• Chemical v physical changes
• 6 chemical groups
• Complexity of food

4
Physical Aspects

• States of matter
• Energy transfer
• Uniqueness of water
• Dispersions

5
States of Matter

• Solid
• Liquid
• Vapor pressure
• Evaporation
• Surface tension
• Interfacial tension
• Gas

6
Energy Transfer

• Mechanical energy
• Radiation
• Conduction
• Convection
• Mass transfer

7
Uniqueness of Water
Steam

Heat of Vaporizaton
540 Cal
80 Cal
Water
Heat of fusion
Ice
8
Uniqueness of Water
Steam

Boiling Point
Atmospheric pressure
solute
Water
Freezing point
Ice
9
Water activity

• Bound vs free water
• 1.0 is highest
• Implication in foods
• Altering water activity

10
Dispersions

• Coarse suspensions
• Temporary dispersions that separate quickly
• Colloidal dispersions
• Molecules intermediate in size in comparison to
  other dispersions
• True solutions
• Smallest particle size and most stable dispersion

11
Colloidal Dispersions

• Two phases
• Hydrophilic vs hydrophobic
• Types of colloidal dispersions
• Gel Sol
• Foam Emulsion

12
True Solution

• Dispersion in which ions/molecules no larger than
  one millimicron are dissolved in a liquid.
• Solute vs. solvent
• Concentration
• Refers to amount of solute dissolved
• Level of saturation

13
Colligative properties of solutions

• Effect of solute on boiling/freezing points
• Presence of solute decreases vapor pressure thus
  increasing boiling point
• Solute decreases freezing point b/c solute
  molecules interfere with crystallization

14
Colligative properties of solutions

• Osmosis
• Movement of solvent from area of low solute
  concentration through semi-permeable membrane to
  area of high solute concentration in effort to
  equalize