Transcript Functional and working properties

Carbohydrate and its functional and
working properties in food products
Many foods contain some carbohydrate but the amounts of sugars,
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.
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, also known in the UK as non-starch polysaccharides (NSP), e.g.
cellulose and pectin and guar gum is found in fruits, vegetables,
beans and cereals.
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Extension
Functional properties
Carbohydrates perform different functions in food products. They:
• Contribute to the chewiness, colour and sweet flavour of caramel
• Help cause the colour change of bread, toast and bakery products
• Thicken products such as sauces and custards
• 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-organism . It is
used extensively in the production of jam, marmalade and some canned fruit. Sugar
is an important ingredient in determining the shelf-life of a product.
• Jelling: some fruits, such as apples and blackcurrants, are rich sources of pectin.
Pectin is used as a jelling agent in the production of jam.
Dextrinisation
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Foods which are baked, grilled or roasted undergo colour, odour and flavour
changes. This is due to a reaction involving protein and a reducing sugar. These
polymerise to form complex brown coloured compounds called dextrins. These
compounds contribute to the colour and flavour of many foods such as toast, bread
and croissants. This is known as non-enzymic browning (Maillard reaction).
•
Parts of amino acid and sugar molecules in food combine, when heated, to form
brown compounds which change it’s colour, odour and flavour.
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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.
Overheating will cause the substance to become bitter and dark.
The effect of dry heat on sugar is to cause melting, browning or caramelisation
and eventually burning.
Moist
heat
Grains
dissolve
Continued
heat
Forms a
syrup
Caramelise
Burn
e.g. browning of sugar on top of crème brulèe, production of spun sugar
work.
Crème Brulèe:
http://www.youtube.com/watch?v=8nTcoAOyOvM&feature=related
Spun Sugar:
http://www.youtube.com/watch?v=Qoe8UPvVe2U&feature=related
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Gelatinisation
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The process by which a gel is formed. It is usually associated with the thickening
process of starchy foods in conjunction with a liquid and heat, in processes such
as sauce making, cooking potatoes, pasta, rice. e.g. custard & other sauces
which use flour or corn flour, pasta, rice, potatoes
Starches absorb a large quantity of water and the starch eventually cross-links to
form a three dimensional network. The temperature at which the starch
gelatinises depends upon the starch used.
When a suspension of starch in liquid is heated, the liquid penetrates the outer
layers of the granules and the granules begin to swell and eventually rupture,
absorbing liquid which thickens the mixture. This occurs from 60°C to 80°C
The granules swell until they are as much as 5 times the original
At 80°C the starch granules begin to break up dispersing the contents into the
liquid
The long chain molecules unfold and the mixture becomes more viscous (thicker)
to become a sol
On cooling, if enough starch is used, a gel forms and it becomes solid. This
process is used in the production of blancmange
Heat
Starch grains soften
& absorb water
© Food – a fact of life 2009
Swell until
they break
Makes the mixture
thicker
Retrogradation
• This is the reverse of gelatinisation and is usually seen in relation to
the seepage of water from a thickened sauce.
• Water is expelled from the gel and the starch gradually changes its
characteristics. In the case of bread, when it stales, it loses water
and this can be considered a retrogradation.
• Starches containing amylose gel best, because the molecules are
spiral shaped and form a network in which water is trapped. This
produces a rigid gel.
• Amylose molecules tend to unwind in time however, producing a
watery deposit, an opaque gel and a pulpy, spongy texture.
• It occurs mainly when foods are frozen and thawed.
• High amylopectin starches do not retrograde easily
• Some retrogradation can be reversed, e.g. the bread can be
reheated to regain some of the original texture.
© Food – a fact of life 2009
Protein and its functional and working
properties in food products
Most foods contain protein, such as collagen in meat, gluten in wheat flour and albumin
in egg white
Some types of protein help with reactions – these are called enzymes, whilst others form
part of the structure of the cells
Protein performs different functions in food products. They:
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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.
Denaturation
Denaturation is the change in structure of protein molecules. It is the break down of links
in the chains of amino acids during heating. The process results in the unfolding of
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. It is the setting of proteins during heating.
For example, when egg white is cooked it changes colour and becomes firmer or sets.
This change is irreversible.
Another form of coagulation occurs in the production of cheese.
Rennin (an enzyme from a calf’s stomach) is added to milk causing
the protein casein to clot, producing curds (solid) and whey (liquid).
Other applications of coagulation are:
• yogurt making
• thickening of sauces with beaten egg
• binding ingredients together, e.g. fish, cakes
• providing a coating for products, e.g. scotch eggs
Temperature raised slowly (kept at around 66°C) = protein will set gradually (coagulate)
& not become too hard. e.g. poached egg
Temperature raised above 100°C = protein will set quickly (coagulate) and harden.
e.g. fried egg
DENATURATION
(break down when heated)
COAGULATION
(quickly/slowing depending on temperature)
High temperatures also cause protein foods to brown, giving added flavour to meat & look more
appealing/appetising.
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Gluten formation
Two proteins, gliadin and glutenin, found in wheat flour, form gluten when
mixed with water.
Gluten is strong, elastic and forms a 3D network in dough.
In the production of bread, kneading helps untangle the gluten strands and
align them.
Gluten helps give structure to the bread and keeps in the gases that expand
during cooking.
The amount and type of protein present depends on the flour type and
quality. Strong flour contains a maximum of 17% protein, plain flour 10%.
A cross section is shown below of under developed dough and weak
or soft flour 8% respectively.
Products that require short or non-elastic textures, such as biscuits and
cakes, use flours with lower protein contents.
https://www.youtube.com/watch?v=zDEcvSc2UKA
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Gelation
Gelatine is a protein which is extracted from collagen, present in
connective tissue in meat.
When it is mixed with warm water the gelatine protein molecules start
to unwind.
Although on cooling a stable network is formed, trapping the liquid.
Gelation is reversible.
Syneresis
• Syneresis is the shrinkage of a gel and the subsequent loss of liquid
• Gels affected by syneresis can be based upon protein
• An example of syneresis is scrambled egg, which if overcooked,
shrinks and produces a liquid
• Another example is jelly left to stand, producing a pool of water
around the base
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Fat and its functional and working
properties in food products
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.
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.
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
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Shortening
Shortcrust pastry, biscuits and shortbread rely on fat to give them their
characteristic crumbly texture.
The fats coats 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.
There are distinctive colours associated with the type of fat used. Margarine
produces a golden colour and lard produces a pale yellow. A
compromise is sometimes reached by using a combination of the two.
Plasticity
Fats do not melt at fixed temperatures, but over a range. This property is
called plasticity. It gives all fats unique character.
The plasticity is due to the mixture of triglycerides, each with it’s own melting
point. 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.
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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.
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.
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.
Glaze
Placed on hot vegetables, some fats, e.g. butter or margarine, give glossy appearance.
Fats also add shine to sauces.
© Food – a fact of life 2009
Functional properties
overview
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
Foundation
Aerating
Product / Ingredient
Meringue / Egg white
Scone / Self raising flour
Cake / Baking powder
Wholemeal bread /
Yeast
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How do you aerate?
Why does it aerate?
Whisk egg white to produce a
Protein in egg white denature and
foam. Fold foam with other
trap air in a stable network
ingredients to create light mixture,
e.g. sugar.
Raising agents in the flour react
Combine self raising flour with
with water to produce carbon
other ingredients and bake.
dioxide which expands on heating.
Add baking powder to flour, mix
with other ingredients and bake.
Baking powder reacts with water
to produce carbon dioxide which
expands on heating.
Yeast releases carbon dioxide and
Sprinkle dried yeast into flour
alcohol during rising and baking,
mixture and add liquid, knead the causing the dough to expand - the
dough and leave to rise then
alcohol and water evaporate
bake.
during baking.
Binding
Product / Ingredient
How do you bind?
Nann bread / Yogurt
Combine yogurt with main
ingredients and stir.
Pancake / Milk
Whisk milk gradually into other
ingredients until smooth.
Fish cake / Egg
Pastry / Water
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Why does it bind?
Liquid present in yogurt is absorbed by the
starch granules and hydrates proteins in
the flour to form a network.
Milk disperses the protein from the egg
and suspends the starch granules from
the flour in a smooth batter mixture.
Raw egg combines the other ingredients
Mix egg with other ingredients. and during cooking the protein in the egg
coagulates keeping the fish cake
together.
Water is absorbed by the starch granules,
Stir water into flour mixture until a
hydrating proteins in the flour to form a
dough is formed.
network.
Bulking
Product / Ingredient
Fruit Pie Filling / Sugar
Vegetable Samosa / Potato
Nut Roast / Breadcrumbs
Cottage Pie / Textured
Vegetable
Protein (TVP)
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How do you bulk?
Why does it bulk?
Boil sugar with fruit juice, reduce Water evaporates and the
mixture to thickness required, add mixture caramelises producing
prepared fruit, assemble pie and a syrup or a thick puree.
bake.
Prepare filling using potato as the
Potato absorbs flavours and
main ingredient, add extra liquid and liquid, retaining its shape and
seasoning if needed, assemble and
texture - forming the body of
cook.
the filling.
Stir
breadcrumbs
with
other Breadcrumbs absorb flavours
ingredients, add extra liquid and and liquid and bind to other
seasoning if needed, bake.
ingredients.
Mix reconstituted TVP with minced
meat and vegetables, add extra
liquid and seasoning if needed, layer
mashed potato on top.
TVP absorbs flavours and liquid,
mimics the sensory properties of
meat - forming the main part of
the filling.
Glazing
Product / Ingredient
Sausage Roll / Egg
Bun / Sugar
Pie / Milk
Gammon / Honey
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How do you glaze?
Why does it glaze?
The surface of the sausage roll takes
Brush beaten egg over the surface on
of the sausage roll before baking. a shiny golden brown appearance
due to coagulation of egg proteins
and the Maillard browning reaction.
Boil sugar with water or milk, brush The liquid evaporates and
over the surface of the bun after
caramelises producing a syrup,
baking.
which gives the buns a shiny and
sticky appearance.
The surface of the pie takes on a
Brush milk over the surface of the
matt light brown appearance due
pie before baking.
to the Maillard browning reaction.
Spread honey over the gammon
before roasting.
The honey caramelises giving a shiny
brown appearance.
Setting
Product / Ingredient
How do you set?
Why does it set?
Blend cornflour with a little milk and
The corn starch grains swell and
sugar to a smooth paste, gradually
Blancmange / Cornflour add to hot milk, stir and heat to boiling rupture, releasing starch which
absorbs the liquid, the mixture sets
point - allow to cool.
on cooling.
Mix gelatine with a little warm water
The gelatine swells, forming a
until it has dissolved, add to remaining
Cold Soufflé
network which traps water forming
mixture slowly to avoid lumps forming.
a gel.
Mix egg with other fillings, pour mixture On heating the egg protein
Quiche
into pastry case and bake.
coagulates, setting the mixture.
Jam
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Heat fruit and sugar, add extra pectin,
The pectin, sugar and acid form a
water and citric acid if needed - boil
until setting point is reached - allow to gel which traps the water.
cool.
Thickening
Product / Ingredient
How do you thicken?
Sauce / Flour
Blend the flour with melted fat,
gradually add the liquid, stir and
heat to boiling point.
Egg custard / Egg
Add beaten egg slowly to the milk
The egg coagulates on heating
and sugar mixture, heat gently,
and thickens the mixture.
stirring continuously until thick.
Soup / Potato
Syrup / Sugar
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Combine chunks of potato with
other solid ingredients, add liquid
and heat.
Why does it thicken?
Starch granules in the flour swell,
rupture and release starch which
absorbs the liquid causing the
mixture to gelatinise.
Potato starch is released from the
cells on heating and absorbs liquid
which gelatinise and thicken the
soup.
Heat sugar and water (or fruit juice)
The water evaporates and the
together, reduce the mixture to the
mixture caramelises producing a
thickness required.
syrup.