Proteins

• What is the definition of chemical bond?

  Bonds that hold large protein molecules together in compact, folded bundles
• What is the definition of denaturation?

  The chemical bonds have broken and the protein molecule has unfolded and changed shape
• What is the definition of coagulation?

  The joining together of lots of denatured protein molecules, which changes the appearance and texture of the food
• Structure of proteins

  . Proteins are large molecules, made up of individual units called amino acids

  . As they are so large, protein molecules are often folded into compact 'bundles' so that they take up less space

  . Proteins are complex molecules which contain the elements: Oxygen, Carbo, Hydrogen, Nitrogen and sometime Sulphur and Phosphorus

  . Chemical bonds in the protein molecule bundle hold it together and stop it unfolding
• Denaturation

  . Protein molecules can easily be denatured

  . This means that the chemical bonds that hold the protein molecule bundle together can be broken, which makes the protein molecule bundle unfold and change shape

  . Denaturation of protein molecules can be caused by:

  - heat (e.g. frying or boiling an egg)

  - acids (e.g. when adding lemon juice to cream or marinating meat in lime, tomato or lemon juice)

  - air bubbles (e.g. in a whisked sponge mixture)

  - mechanical agitation (e.g. when whisking egg whites for meringue)
• What happens to denatured protein molecules?

  They become larger and take up more space
• What is coagulation in proteins?

  It is when denatured proteins join in large groups
• How do coagulated protein molecules affect water in food?

  They trap and hold water in pockets
• What changes occur in food as coagulation continues?

  The appearance and texture of the food changes
• What happens to egg whites when boiled?

  They change from transparent to opaque white
• Why are proteins in eggs useful in recipes?

  They hold other ingredients together
• How does boiling affect the state of an egg?

  The whole egg changes from liquid to solid
• What happens when protein foods are overcooked?

  Coagulated proteins tighten and squeeze out water
• Why is overcooked meat or fish often dry and chewy?

  Because water is squeezed out of proteins
• What happens to overcooked scrambled eggs?

  They become rubbery and watery
• What do consumers expect from baked products like bread and cakes?

  A light and open texture
• Why is a raising agent added to the uncooked mixture?

  To introduce gas bubbles that expand when baked
• What must the mixture be able to do for the gas bubbles to expand?

  Stretch and rise
• What protein is responsible for the ability of baked mixtures to stretch and rise?

  Gluten
• What type of flour contains gluten?

  Wheat flour
• Why is strong plain flour suitable for bread making?

  It contains a higher proportion of gluten
• What two proteins combine to form gluten?

  Glutenin and gliadin
• What happens when liquid is added to flour?

  The proteins mix to form a gluten network
• What is the process of kneading dough intended to achieve?

  Make it smooth and stretchy
• What property does gluten give to the dough?

  Plasticity
• What does the elasticity of gluten allow the dough to do?

  Shrink back when stretching stops
• Why do gluten molecules behave like coiled wires?

  They bend in different places along their length
• What happens to gluten molecules when dough is kneaded?

  The coils and bends straighten out
• Why is stretching and shaping important for bread making?

  To allow dough to expand from CO2 bubbles
• What does the gluten network do during baking?

  Traps bubbles and sets to form texture
• What are the key functions of gluten in dough?

  • Provides plasticity for shaping
  • Offers elasticity for returning to shape
  • Traps gas bubbles during rising
  • Contributes to the final texture of baked goods
• What is a common pastry recipe that requires resting the dough?

  Shortcrust pastry
• Why is resting the dough important in pastry making?

  It allows stretched gluten molecules to relax
• What happens to gluten molecules as the pastry rests?

  They return to their original size and shape
• What is the consequence of not resting the dough before baking?

  Gluten molecules remain stretched and shrink rapidly
• How does the heat of the oven affect un-rested dough?

  It causes the stretched gluten to shrink rapidly
• What may happen if the pastry case shrinks during baking?

  The filling may leak out of the flan
• What is produced by creating a foam in foods like mousses and meringue?

  Light texture
• How are foams formed?

  Gases are trapped inside a liquid
• What type of foam is created when making meringue?

  Gas (air)-in-liquid foam