Transcript Functional properties overview.

Functional Poperties
overview
© BRITISH NUTRITION FOUNDATION 2016
Learning objectives
To understand the functional
properties of carbohydrate,
protein and fats in food.
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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.
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Carbohydrate
The term carbohydrate covers
a wide range of natural
compounds, including:
• starch;
• sugar,
• fibre.
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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.
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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.
There are two types of fibre:
Soluble fibre - found in fruit,
vegetables, pulses and oats.
Insoluble fibre - found in cereal such
as bread and pasta.
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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.
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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 nonenzymic browning (Maillard
reaction).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Review of the learning
objectives
To understand the functional
properties of carbohydrate,
protein and fats in food.
© BRITISH NUTRITION FOUNDATION 2016
British Nutrition Foundation
Imperial House
15-19 Kingsway
London WC2B 6UN
Telephone: 020 7557 7930
Email: [email protected]
Web: www.nutrition.org.uk www.foodafactoflife.org.uk
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