Download e. functions of food

FUNTIONS AND PROPERTIES OF FOOD
THIS SECTION WILL LOOK AT THE FOLLOWING;
• CARBOHYDRATES (STARCH AND SUGARS)
• PROTEIN
• FATS AND OILS
Their functions in food products
CARBOHYDRATES
Job (function in the body) – Gives the body energy
There are 2 types or carbohydrate;
• Starches – found in flour, potatoes, pasta, rice and bread
• Sugars – found in fruit, drinks and sweet baked goods
Starch
TYPES
• Flour is high in starch
• Cornflour and arrowroot are pure starch
USES
• Bulking agent – flour is often the main ingredient in many food products. The starch forms
the main structure of the product e.g. pastry
• Thickening agent – raw starch tastes floury and needs to be cooked. When starch is heated in
liquid, the walls of the starch become soft and hollow and allow liquid to pass through them.
This makes the granules swell until they burst. This process is called gelatinisation (see next
slide)
• Gelling agent – after gelatinisation the liquid forms a gel. On cooling the gel solidifies. When
reheated it goes back to a liquid e.g. custard where cornflour is used
STARCH - GELATINISATION
Starch granules do
not dissolve in liquid.
Instead they form a
suspension
Suspension – a solid
held in a liquid
When heated at
60◦c, the starch
granules begin to
absorb the liquid
and swell.
At 80◦c the particles will have absorbed
about 5 times their volume of water
until they burst open and release
starch, thickening the liquid.
Gelatinisation is complete when the
liquid reaches boiling point, 100◦c
CARBOHYDRATES – FUNCTIONS OF SUGAR
Preserves food. It
creates unsuitable
conditions for bacteria
to grow e.g. in Jam
Sweetens drinks and
food e.g. coffee
Flavour. It improves or
changes the flavour by
removing sour taste
e.g. in tomato sauce
Bulking agent. Gives
the food texture e.g.
ice cream and cakes
Colour. When sugar is
heated it turns golden
brown. This is called
caramelisation.
Aerates. When sugar
is beaten with butter
or eggs it helps trap
air to make cakes light
Stabilises whisked
mixtures e.g.
meringue because it
strengthens the foam
Keeps food moist and
extends shelf life
PROTEIN
Job (function in the body) – growth and repair in the body
Protein foods are made
up of amino acids that
are linked together like
the links in a chain.
When protein foods are
heated the links in the
chain change and this
alters the structure of the
food.
Example – a raw egg can
change depending on if it
is fried, scrambled or
boiled.
Bind – bind dry
ingredients. When
heated the eggs
hold the ingredients
together e.g.
burgers
Enrich – in sauces by
adding colour and
nutritional value
USES OF EGGS
Coagulation –
setting a mixture to
hold a frim structure
e.g. quiche. Full
coagulation
happens at 70◦c
Aerate – trap air
when beaten e.g.
cakes, meringue
Coat/enrobe – the
eggs act like a glue
and hold dry
coating to a surface
e.g breadcrumbs
Emulsify – eggs are
used to stop oil and
water separating;
allowing an
emulsion to form
e.g. mayo
Glaze – they add
colour and give
products a shiny glaze
e.g. pastry
Thicken – the
protein sets when
heated e.g. custard
FATS AND OILS
Job (function in the body) – Protection and insulation and gives some energy
Fats are produced from 3
different sources;
Animals
Fish
Vegetables
Saturated Fats
• Mostly found in solid fats
e.g. butter
• High in cholesterol
compared to other fats
Unsaturated Fats
• Mostly found in fats that are
liquid at room temperature.
• Mainly in vegetable oils e.g.
cooking oils
• Less cholesterol than
saturated fats
Required to aerate
food. When fat is
creamed with
sugar it helps trap
air.
Prevents lumps of
flour forming in a
sauce e.g. white
sauce
Adds flaky texture
to pastry. Fat
helps to separate
layers by creating
steam
Shortens pastry to
give it a crumbly
texture – see
Section A
Function of Fats and
Oils
Acts as a cooking
medium for
roasting foods e.g.
chicken
Extends shelf life
of baked products
by keeping the
product moist.
Adds distinct
flavours and
odours to food e.g.
buttery biscuits
Adds colour and
shine to food e.g.
scones