Functional and Chemical properties of food Flashcards
Definition of protein denaturation
when food is cooked proteins denature, meaning the chemical bonds holding their structure together break down
-proteins unravel and their shape changes
Name 4 ways proteins can be denatured
- Physical agitation
- Changes in temperature
- Acids
- Heat
Name the process that occurs once protein molecules have been denatured
protein coagulation
Definition of protein coagulation
-once they have been denatured protein molecules collide with other protein molecules and coagulate (join together)
What does protein coagulation change in a food
The appearance and texture
Definition of foam formation
Foams form when gas becomes trapped (aeration) inside a liquid
Definition of gluten formation
Gluten is formed when water is mixed with flour to make dough
What foods is gluten found in
bread
pasta
cakes
pastries
What is gelatinisation
It helps to thicken foods containing starch
Describe the steps of gelatinisation
- starch molecules become suspended when first mixed with liquid
- starch molecules then start to break when heated with water, allowing water molecules to enter
- water is absorbed and starch granules swell in size and soften
- between 62 and 80 degrees starch granules burst open and release starch into liquid causing it to thicken
- when it cools liquid solidifies and a solid gel is formed
When does dextrinisation occur
It occurs when starch is exposed to dry heat
How does dextrinisation occur
When starchy foods are cooked with dry heat starch molecules in food break down into dextrins
How does dextrinisation change food
gives food a browner colour
crispier texture
different taste
What is caramelisation
The browning and change in flavour of sugar when heated
Describe the steps of caramelisation- what food is like when it is first caramelised
- at first the liquid is runny and has a very sweet taste
- as time passes it becomes more like a smooth caramel
- then it turns harder and as it cools becomes more like candy
How does caramelisation change food
gives desserts like crème brulee and apple pie extra sweetness
What is shortening
When a fat coats starch and prevents the water from lengthening the gluten
-Gives food a crumbly texture
How does shortening occur
- Rub fat into flour and cover flour particles with fat giving the flour particles a waterproof coating
- This waterproof coating prevents long gluten molecules forming
- So dough can’t become stretchy and so keeps a short texture
What is plasticity
The ability to be spread and shaped
How does plasticity occur
- Fats contain a mixture of different triglycerides
- These different triglycerides all melt at different temperatures so fats gradually soften over a range of temperatures rather than just melting on
What does emulsification do
Emulsification keeps oil and water in a stable emulsion
How does emulsification occur
- Molecules in an emulsifier have two different ends one is hydrophilic (attracted to water) and the other is hydrophobic (repulsed by water)
- when you add an emulsifier the water molecules bond to the hydrophilic side and the oil molecules bond to the hydrophobic side
- this holds water and oil together in a stable emulsion preventing them from separating
What are examples of emulsions
Milk, margarine, mayonnaise
Which types of raising agents produce carbon dioxide
- Chemical
- Biological
How do chemical raising agents produce carbon dioxide
-when heated bicarbonate of soda breaks down to produce carbon dioxide bubbles that expand to make the mixture rise
How do biological raising agents produce carbon dioxide
- Yeast is a microorganism that causes fermentation- a process that releases alcohol and carbon dioxide
- When carbon dioxide is released and trapped in dough, it causes the dough to rise
Name a chemical raising agent
Bicarbonate of soda
Name a biological raising agent
Yeast
Which types of raising agents add steam or air to the mixture
- Steam
- Mechanical
How does the steam raising agent add steam to the mixture
- when using a very hot oven to cook a mixture it contains lots of liquid
- this water leaves the mixture as steam and as it rises it raises the mixture up and food becomes more solid
How do mechanical raising agents add air to the mixture
-Air can be folded into mixtures and doughs:
using a spoon, repeatedlty folding the mixture over itself trapping the air
pastry doughs can be folded in layers traping the air
- Whisking
- Beating
- Sieving flour
- Creaming
Name 5 reasons why food is cooked
- make it safe to eat
- improve shelf life
- develop flavours
- improve texture
- give variety in diet
Name the 3 ways heat can be transferred
- convection
- conduction
- radiation
Definition of convection
-transfer of heat energy through the vibration of particles
Describe what happens in convection when a pan is placed on the hob
- when a pan is placed on the hob heat energy from hob causes particles to vibrate and gain heat energy
- these particles collide with nearby particles passing some of their extra heat energy to them
- when food is placed in pan- heat energy is transferred from the pan to particles in the food
Definition of conduction
-transfer of heat energy through gases/ liquids
Describe what happens in conduction when you heat up a liquid
- when you heat a liquid, liquid near heat source heats up fast
- As warm air rises, colder liquid takes its place
- as process continues you end up with convection currents resulting in whole fluid being heated
Definition of radiation
-transfer of heat energy through waves of radiation
Describe what happens in radiation when using a grill/ toaster
-they emit waves of radiation which are absorbed and heat food up
Name 6 water-based cooking methods
- boiling- healthy method
- steaming-healthy
- simmering
- blanching
- poaching
- braising
Name 2 fat-based cooking methods
- shallow frying
- stir fry
Name 4 dry-methods of cooking
- baking
- roasting
- grilling
- dry frying
definition of aeration
-adding air to a mixture through baking/ whisking
name a food which shows visible denaturation and coagulation
frying an egg
