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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. 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

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

  2. Homework F.6: Texture • Read F6– Texture pp. 487-488 • Do Qs 38-42 • on p 493

  3. 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.

  4. 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

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

  6. 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…

  7. 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 !

  8. Soap

  9. Soap

  10. 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 ).

  11. 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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