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Food Chemistry . Chapter 17 in Green / Damjii Chapter X in Nuess Chapter X in Oxford Study (no resource in Chang). Homework. F.6: Texture. Read F6– Texture pp . 487-488 Do Qs 38-42 on p 493. F.6.1 : Describe a dispersed system in food. TEXTURE depends on

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food chemistry

Food Chemistry

Chapter 17 in Green / Damjii

Chapter X in Nuess

Chapter X in Oxford Study

(no resource in Chang)

homework
Homework

F.6: Texture

  • Read F6– Texture pp. 487-488
  • Do Qs 38-42
  • on p 493
f 6 1 describe a dispersed system in food
F.6.1: Describe a dispersed system in food

TEXTURE depends on

  • Physical properties (hardness, elasticity)
  • Cooking
  • Moisture content

CREAMY TEXTURES valued in many foods depend on

  • Disperse system
    • stablized (do not separate… or separate v. slowly)
    • macroscopically homogeneous mixture of 2 immiscible phases
    • A typical FOOD disperse system will involve a liquid as one of the immiscible phases.
slide4
F.6.2: Distinguish between the following types of dispersed systems – suspensions, emulsions, and foams in foods.
  • Dispersed system: LIQUID / SOLID
    • Suspension (sol)
      • Solid particles suspended in a liquid
        • EX: blood (solid red/white blood cells suspended in plasma)
    • Gel
      • Liquid particles suspended in a solid
        • EX: fruit jelly – water trapped in a protein matrix
slide5

Dispersed system: LIQUID / GAS

    • Foam
      • Gas trapped in a liquid medium
        • EX: whipped cream, egg whites
    • Aerosols
      • Liquid droplets suspended in a gas
        • EX:
slide6

Dispersed system: LIQUID / LIQUID

    • Emulsion
      • Stable blend of 2 immiscible liquids
        • EX: mayonnaise (oil droplets suspending in water)
      • Emulsifiers are often used to promote the mixing of 2 phases…
f 6 3 describe the action of emulsifiers
F.6.3: Describe the action of emulsifiers

Emulsifiers

  • molecules that can bond to both phases
  • found at the surface between the phases
  • often called surfactants
  • similar to what happens with soap !
f 6 3 describe the action of emulsifiers1
F.6.3: Describe the action of emulsifiers

Emulsifiers

  • Lecithin – a phospholipid which is found in egg yolks
  • Contains polar end… hydrophilic
    • Bonds to water
  • Contains nonpolarend… hydrophobic
    • Bonds to non aqueous phase
    • ex: mayo made by beating oil and

vinegar with egg yolks

      • hydrophilic end of lecithin bonds to

vinegar and hydrophobic end bonds

to oil

      • Surfactant (lecithin) surrounds oil

droplets… suspending them within the

aqueous phase ( vinegar ).

f 6 3 describe the action of emulsifiers2
F.6.3: Describe the action of emulsifiers

Stabilizers

  • Often added to stablize dispersed states… keep them from separating.
  • Inorganic phosphates (trisodium phosphate) can stablize emulsions
  • Metal bowls – chefs prefer these to beat egg whites… minute traces of the metal are incorporated into the foam and actually stabilize it.
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