Transcript Nutrients - Food a fact of life

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Functional properties
overview
© Food – a fact of life 2009
Foundation
Learning objectives
• To understand the functional properties of
carbohydrate, protein and fats in food.
© Food – a fact of life 2009
Introduction
Ingredients have a range of different properties.
Sometimes these are called functions.
The main nutrient provided by an ingredient gives it a
range of properties during cooking.
Carbohydrate, protein and fat all have a range of
different properties.
© Food – a fact of life 2009
Carbohydrate
The term carbohydrate covers a wide range
of natural compounds, including:
• starch;
• sugar,
• fibre or non starch polysaccharides (NSP).
© Food – a fact of life 2009
Carbohydrate in food
Many foods contain some carbohydrate, but the
amounts of sugar, starch and fibre differ.
Sugars are naturally present in foods such as milk , fruits,
vegetables and honey. In the UK, sugar beet and sugar
cane are the most common sources of sugar. Honey,
treacle and golden syrup are also popular.
Starch is present in foods such as potatoes, bread, rice
and pasta.
© Food – a fact of life 2009
Carbohydrate in food
Fibre is present in whole grains, fruits and vegetables,
especially the skin covering of seeds.
It is a mixture of substances (mainly complex
carbohydrates) which cannot be digested in the small
intestine.
Fibre (NSP), e.g. cellulose and pectin and guar gum is
found in fruits, vegetables, beans and cereals.
© Food – a fact of life 2009
Carbohydrate
Carbohydrate performs different functions in food
products.
They:
• help cause the colour change of bread, toast
and bakery products;
• contribute to the chewiness, colour and sweet
flavour of caramel;
• thicken products such as sauces and custards.
© Food – a fact of life 2009
Dextrinisation
Foods which are baked, grilled or roasted undergo
colour, odour and flavour changes. This process is
called dextrinisation.
Dextrinisation contributes to the colour and flavour of
many foods such as toast, bread and croissants. This is
known as non-enzymic browning (Maillard reaction).
© Food – a fact of life 2009
Caramelisation
When sucrose (sugar) is heated above its melting point
it undergoes a physical change to produce caramel.
This happens more readily without water, however
syrups will caramelise with rapid heating.
This process is used extensively in the production of
confectionary.
© Food – a fact of life 2009
Gelatinisation
When starch is mixed with liquid and heated, the starch
granules swell and eventually rupture, absorbing liquid
which thickens the mixture, e.g. a white sauce.
On cooling, if enough starch is used, a gel forms. This
process is used to make blancmange.
© Food – a fact of life 2009
Other Characteristics
Flavouring
Sugar, e.g. sucrose, may be used to flavour many
products such as drinks, cakes, tomato sauce and
confectionary. It supplies sweetness and mouth feel.
Preserving
Sugar in high concentrations prevents the growth of
micro-organisms.
It is used extensively in the production of jam, marmalade
and some canned fruit.
Jelling
Some fruits, such as apples and blackcurrants,
are rich sources of pectin.
Pectin is used as a jelling agent when making jam.
© Food – a fact of life 2009
Protein
Protein performs different functions in food
products.
They:
• aerate foods, e.g. whisking egg whites;
• thicken sauces, e.g. egg custard;
• bind ingredients together, e.g. fish cakes;
• form structures, e.g. gluten development in
bread;
• gel, e.g. lime jelly.
© Food – a fact of life 2009
Denaturation
Denaturation is the change in structure of protein
molecules.
Factors which contribute to denaturation are heat, salts,
pH and mechanical action.
Denaturation is a partially reversible change. For
example, when an egg white is whisked it incorporates
air to form a foam.
If the foam is left to stand, it will
collapse back to form liquid egg
white.
© Food – a fact of life 2009
Coagulation
Coagulation follows denaturation. For example, when
egg white is cooked it changes colour and becomes
firmer or sets.
This change is irreversible.
Other applications of coagulation are:
• cheese and yogurt making;
• thickening of sauces with beaten egg;
• binding ingredients together, e.g. fish, cakes;
• providing a coating for products, e.g. scotch eggs.
© Food – a fact of life 2009
Gluten
Gluten is a composite of proteins joined with starch, it is
acquired by washing wheat flour to dissolve the starch,
leaving the gluten.
Gluten is strong, elastic and forms a 3D network in
dough. When making bread, kneading helps to
develop the gluten and make the dough more elastic.
Gluten helps give structure to bread and keeps in the
gases that expand during cooking.
© Food – a fact of life 2009
Gelation
Gelatine is a protein which is from collagen, present in
connective tissue in meat.
When it is mixed with warm water the gelatine proteins
unwind.
On cooling a gel is formed, trapping the liquid, e.g.
jelly.
Gelation is reversible.
© Food – a fact of life 2009
Fats
Fats performs different functions in food products.
They help to:
• add ‘shortness’ or ‘flakiness’ to foods, e.g.
shortbread, pastry;
• provide a range of textures and cooking mediums;
• glaze foods, e.g. butter on carrots;
• aerate mixtures, e.g. a creamed cake mix;
• add a range of flavours.
© Food – a fact of life 2009
Fats
Fats have a range of properties, which are useful to
exploit during preparing and cooking dishes.
Shortening
Shortcrust pastry, biscuits and shortbread rely on fat to
give them their characteristic crumbly texture.
The fats coat the flour particles and prevents them from
absorbing water. This reduces the formation of gluten
development, which would cause the dough to
become elastic.
Fats such as pure vegetable fats or lard are suitable for
shortening because of their low water content.
© Food – a fact of life 2009
Plasticity
Fats do not melt at fixed temperatures, but
over a range. This property is called
plasticity. It gives all fats unique character.
This is why some fats are solid or liquid at
room temperature, e.g. olive oil and lard.
Some products are formulated with fats with
lower melting points so they can spread from
the fridge, e.g. margarine, or melt on the
tongue, e.g. chocolate. Other fats have a
higher melting point and are used for
cooking, e.g. vegetable oil.
© Food – a fact of life 2009
Aeration
Products such as creamed cakes need air incorporated
into the mixture in order to give a well risen texture.
This is achieved by creaming a fat, such as butter or
margarine, with caster sugar.
Small bubbles of air are incorporated and form a stable
foam.
© Food – a fact of life 2009
Flakiness
Flaky and puff pastry use fat to help separate layers of
gluten and starch formed in the dough. The fat melts
during cooking, leaving minute layers.
The liquid present produces steam which evaporates
and causes the layers to rise.
The fat prevents the layers sticking together.
© Food – a fact of life 2009
Other characteristics
Retention of moisture
Some fats can help retain a bakery product’s moisture
and increase its shelf-life. They may also be used to
baste food being cooked by dry heat, e.g. roast beef.
Glaze
Placed on hot vegetables, some fats give glossy
appearance , e.g. butter or margarine.
Fats also add shine to sauces.
© Food – a fact of life 2009
Sensory attributes
All fats and oils have unique flavours and odours.
Some are more suited for particular purposes than
others, e.g. olive oil for salad dressing (for flavour) and
lard for pastry (due to its blandness).
They can also contribute to the texture of the food, for
example increasing succulence.
© Food – a fact of life 2009
Review of the learning objectives
• To understand the functional properties of
carbohydrate, protein and fats in food.
© Food – a fact of life 2009
For more information visit
www.nutrition.org.uk
www.foodafactoflife.org.uk
© Food – a fact of life 2009