Transcript Lesson 3 functional Properties of food

Functional properties of
food
Year 11: Objectives
What
How
Understand
functional
properties of
foods
Research into
functional properties
and their uses
Outcomes
Bronze
Identify the
functional
properties of
protein,
starch, sugar,
fats and oils
Silver
Be able to explain
the functional
properties of
different food
groups and what
happens when heat
is applied
Why
To be able to apply
them to your own
learning and when
preparing food for
others
Gold
Predict what happens to
the properties of
different foods at key
temperatures, being able
to describe in detail the
terms gelatinisation, gel,
suspension and modified
starch
Carbohydrates - Starch
• 2 main types of carbohydrates
– Starch, found in flour, potatoes, pasta, rice
and bread
– Sugars, found in fruits, drinks and sweet
baked products
– Modified starch is used in commercial
production
Types of starch
• Obtained from cereals such as wheat
and maize
– Wheat flour
– Cornflour
– Arrowroot
Uses of starch
• Bulking – forms the main structure of a
product e.g. In biscuits, cakes and
pastry.
• Thickening agent
– Raw starch tastes floury
– Needs to be cooked
Gelatinisation
1. Starch particles do not dissolve in cold liquid, they
form a suspension.
2. If the liquid isn’t stirred, the starch granules sink
to the bottom, stick together and form lumps.
3. At 60˚C, the starch granules begin to absorb the
liquid and swell.
4. At 80˚C, the granules will have absorbed 5x their
volume until they burst open, releasing starch into
the liquid.
5. Gelatinisation is complete when the liquid reaches
100˚C.
6. When the sauce cools, it gets even thicker, setting
into a gel.
Heat
starch
granules
in liquid
Starch
granules
become
swollen at
60˚C
Starch
granules
burst at
80˚C
The liquid
thickens
and
gelatinizes
at 100˚C
Starch gelatinizes when heated in a liquid, producing a thickened liquid
Effects of Heat
Egg
• White starts to
coagulate until it turns
from a liquid to a solid.
• Egg yolk continues to cook until it
becomes dry and hard.
• Over cooking – green and black ring
[iron sulphur] forms around the yolk.
Cheese
• Fat in the cheese melts and separates.
• Protein coagulates and shrinks.
• Over cooking makes cheese tough and
stringy.
• Makes the cheese hard to digest.
Meat
Kills bacteria.
Makes it tender.
Improves flavour.
As the heat increases the structure of
the meat tightens and it becomes
firmer.
• Meat shrinks in size.
• Colour changes
• Fat melts.
•
•
•
•
Pasta - carbohydrate
• Starch grains start to
soften.
• The pasta absorbs water and swells in
size.
• Change of colour.
• As the temperature increases the
starch escapes.
Vegetables
• Makes the food more digestible.
• Reduces the bulk.
• Vitamins can be lost in water – leached
out. (water soluble vitamins B and C)
• Heat destroys vitamins.
• Over cooking softens the structure.
Sugar
• Dry heat converts the
Starch into a simple sugar DEXTRIN.
• Further cooking cause caramelisation.
• Sugar is heated to very high
temperature, turns brown and thickens
adding flavour.
• Over cooking blackens the mixture.
Bread
• Flour forms the structure.
• When the bread is cooked
dextrinisation occurs.
• Starch from the flour is converted into
sugar, which is caramelised giving the
bread colour.
Why cook foods?
•
•
•
•
•
•
Destroys bacteria.
Short term preservation.
Makes food easier to digest.
More appealing and attractive.
Warm meal.
Enhance flavours.