Food Chemistry Chapter 17 in Green / Damjii Chapter X in Nuess Chapter X in Oxford Study (no resource in Chang)

Homework Read F6– Texture pp Do Qs on p 493 F.6: Texture

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. F.6.1: Describe a dispersed system in food

 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 F.6.2: Distinguish between the following types of dispersed systems – suspensions, emulsions, and foams in foods.

 Dispersed system: LIQUID / GAS  Foam  Gas trapped in a liquid medium  EX: whipped cream, egg whites  Aerosols  Liquid droplets suspended in a gas  EX:

 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…

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 emulsifiers

 Soap

Emulsifiers  Lecithin – a phospholipid which is found in egg yolks  Contains polar end… hydrophilic Bonds to water  Contains nonpolar end… 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 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. F.6.3: Describe the action of emulsifiers