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Protein
Protein is one of the macronutrients
that is essential for growth and repair
of body tissue. It is also crucial to the
healthy functioning of the body.
Protein is made up of complex chains
of molecules called amino acids.
There are 20 different types of amino
acid, each with a specific function in
the body.
Key Terms
– the smallest
units of protein
proteins that do not contain all
the essential amino acids
–
amino acids that cannot be
made by the body
– mixing
different low biological value
proteins to supply all the
essential amino acids
–
proteins that contain all the
essential amino acids
– the part of a food
that performs a particular
function in the body
– vitamins and
minerals that are needed in
small quantities for health
– proteins, fats
and carbohydrates providing
the bulk of our diet
The functions of protein in the diet:
• Used for growth especially in children and pregnant
women.
• Used to repair body tissue after illness, accidents and
surgery; renewal of cell proteins for people of all ages.
• Enzymes vital for metabolism are composed of proteins.
• Hormones, which regulate some important bodily
functions, are composed of protein.
• They provide a secondary source of energy. When the
body has used all the amino acids it needs for
construction, the remainder are ‘burnt’ for energy.
Where can we get it from?
The human body needs all
20 amino acids for the
maintenance of health and
growth.
Eleven of these can be
made up by the body itself,
but the others have to be
obtained through the food
we eat – these are called
essential amino acids.
Sources of protein in the diet
Animal sources include all
meats, such as poultry,
offal and game, as well as
fish, cheese, milk, eggs
and gelatine.
Vegetable sources include
soya beans and soya
products, pulses, beans,
cereal grains and cereal
products, nuts and Quorn.
High biological value proteins
The foods that contain all the essential amino
acids are said to have a high biological value.
Most of these come from animal sources (meat,
fish, poultry and dairy products) plus the
vegetable source of soya.
As the vegetarian market grows, there is a large
range of food products made from soya, such as
soya mince, textured vegetable protein (TVP)
and tofu.
Another HBV protein is Quorn, which is a brand
name for a food product made from
mycoprotein.
There are 3 main types of meat eaten
in the UK…
• These are called red meats (though pork is
sometimes classed as white meat). They’re all
great sources of protein, but too much can cause
health problems like heart disease.
• Meat can be tenderised. You have to partly break
down the fibres in the meat, you can do this by
hitting it with a mallet, marinating it in something
acidic or by cooking it very slowly (this is what
makes casseroles so lovely and tender).
• Meat can dry out during cooking. To avoid this you
can seal the outside of the meat (by cooking it at a
high temperature for the first couple of minutes)this keeps the juices in.
Three main types of poultry…
These are white meats – although
duck’s often called red meat.
Poultry is good source of protein
and B Vitamins and is fairly low in
saturated fat (especially without
the skin!)
But it can be contaminated with
salmonella bacteria, which can
make you seriously ill.
And three main types of fish…
Fish is very nutritious – it contains loads of
vitamins, plus omega 3 oils which are great for
health.
Low biological proteins
Vegetable sources of protein include
cereals, peas, beans, pulses, nuts and
seeds.
As these do not contain all the essential
amino acids they are said to have low
biological value (LBV).
They can easily be combined in a meal
or product to provide all the essential
amino acids. This is called food
combining or complementary proteins.
Meat Analogues
• Meat analogues use either
naturally occurring
ingredients (e.g. Soya bean)
or fermentation technology to
manufacture a food which
has been altered to perform a
particular function
• i.e. act as an alternative to
meat.
Some people choose not to eat meat
because of a variety of ethical, social and
value issues and obtain all their protein
from other sources.
In recent years, manufacturers have
produced many meat-like products, called
‘meat analogues’, which mimic the
sensory properties of meat and can be
used to replace or extend meat in
traditional products, e.g. textured
vegetable protein (TVP), myco-protein and
tofu.
Many of these analogues are also fortified
with vitamins and minerals, e.g. vitamin
B12 and iron.
Textured Vegetable, Protein (TVP)
What is it?
• It is composed of bundles of
short fibres of extruded
soya protein. The globular
soya protein is gelled by
heat and shear to form a
fibrous structure.
• Plain TVP may have a
‘beany’ taste, so needs to
be flavoured.
• Varieties of flavoured TVP
are available.
Uses
• It is used in sausages,
pies, Cornish pasties,
burgers and pasta and
dishes.
Tofu
What is it?
• It is produced from ground
soya beans, which have been
sieved.
• The proteins are coagulated,
producing a soft cheese-like
product.
• Tofu is semisolid and is
available in plain and smoked
forms.
• As it is quite soft, it absorbs
flavours well.
Uses
• It does not have a meaty
texture, yet may be used for
many dishes as a substitute
for meat,
• e.g. in stir -fries and
steamed dishes.
Myco-protein
What is it?
• It is produced by fermentation of
a particular organism (Fusarium
graminearum) to produce fine
fibres, which are formed together
to produce a meat analogue.
• It has similar textural properties
to meat and contains a small
amount of fibre.
• The myco-protein undergoes
forming, cutting and texturising
according to the nature of the
product to be made.
Uses
• Myco-protein absorbs flavours
well and may be cooked in many
different ways.
• It is easily formed into many
different shapes.
• e.g. mince, burgers, fillets and
sausages.
Protein deficiency
Not eating enough protein can cause various
problems:
• In children, growth slows down or stops.
• Digestive upsets are caused as enzymes are
not produced.
• The liver fails to function normally.
• Muscles become weak, so limbs are thin and
the tummy is soft and may look distended.
Apply it!
Answer the following questions:
• List four functions of protein in the diet. (4 marks)
• Explain the difference between HBV and LBV proteins.
(4 marks)
• Explain why you would combine protein foods to
complement each other. (4 marks)
• Give two examples of complementary proteins. (2
marks)
Key points
• Protein is needed for growth and repair of body
tissues.
• Protein is made up of amino acids.
• Good sources of high biological proteins are
meat, fish, cheese, eggs and soya.
• Good sources of low biological value protein are
pulses, cereals and nuts.
Function
 Growth and repair of muscles,
Meat
Poultry
Oily Fish
White Fish
Shellfish
tissues and organs
There are 20 different amino acids which
can combine together to make proteins
such as muscle ; hormones; skin;
haemoglobin
During digestion,
proteins are broken
into amino acids. The
amino acids are
absorbed into the
blood made into new
proteins in the cells of
the body.
The body can make 11 of the amino acids, the other 9 have to come
from the food we eat. These are known as essential amino acids.
Essential amino acids
are found in protein
from animal tissue and
soya bean. These
foods are called High
Biological Value (HBV).
Protein from plant
sources are said to be
Low Biological Value
(LBV) as they are
lacking in one or more
of the essential amino
acids.
Meats (lamb, beef & pork) can be high
in saturated fats but are a good source
of Vitamin B, Iron and Zinc.
Poultry (chicken, duck & turkey) is low
in saturated fat and is a good source of
Vitamin B.
Fish (Oily fish, white fish & shellfish) is
very nutritious as it contains a range of
vitamins and omega 3 oils.
Vegetarians don’t eat meat so get their
protein from beans, lentils, nuts and
alternative proteins like Quorn or Tofu.
Practice Questions 1
1.
What do we need proteins for?
2.
List 3 examples of foods that contain all the essential amino acids.
3.
Name two vitamins or minerals that are contained in each of the following:
a) beef b)pork
4.
Mary is going to cook a steak for dinner. Before she fries it, she bashes it with a mallet. Explain
why she does this.
5.
Give 1 advantage and 1 disadvantage of eating white meats.
6.
What are the three main types of fish? Give an example of each type.
7.
How can someone on a vegetarian diet ensure they get the required amount of protein?
8.
a) what does ‘marinate’ mean?
b) why are alternative protein foods often marinated?
Eggs
We mainly eat hens’ eggs, but goose, duck and
quail eggs are popular with some people.
Eggs have lots of uses and functions in
cooking…
Thickening, e.g. in custard or
quiche – egg white coagulates
(becomes solid) at 60ºC and yolk
at 70ºC, so when it reaches
these temperatures it sets and
stays ‘thickened’.
Binding, e.g. in burgers
– coagulation sticks the
ingredients together as
they cook.
Aeration, e.g. in cakes –
egg white traps air
when it’s beaten,
because the protein
stretches.
Emulisifcation, e.g. in salad dressings – oil
and water mixed together form an
emulsion. But the emulsion usually
separates after a while. Lecithin, found in
egg yolk, keeps the emulsion stable (stops
it separating again). That’s why egg yolks
are used in mayonnaise.
Coating or enrobing –
eggs help dry
ingredients like
breadcrumbs to stick to
food
Glazing, e.g. on bagels –
brushing egg over bread
gives it a glossy finish
when it’s cooked.
Eggs may contain Salmonella
1. Raw eggs may contain the bacteria salmonella – which
causes severe food poisoning. (You can also get it from
chicken that isn’t cooked properly!)
2. It’s very important that eggs are cooked thoroughly so
that all bacteria are destroyed.
3. You should be extra careful when cooking eggs to be
eaten by pregnant women, babies and elderly or frail
people.
4. Manufacturers often use dried or pasteurised egg to be on
the safe side, like for mayonnaise.
Be careful with how you cook your
eggs…
The way you cook an egg can make a lot of
difference to how healthy it is.
Boiled and poached eggs are nice and healthy
because they’re cooked using no fat.
Scrambled eggs are healthy – and if you do them
in the microwave you don’t need any fat.
A lot of people like fried eggs though – and these
can absorb a lot of fat from oil. It’s best to use oils
with unsaturated fat and drain off as much of the
oil as possible before eating them.
Practice Questions 2
1. List 5 nutrients contained in all eggs.
2. Explain how eggs can be used in each of the following ways
and give an example product or food for each:
a) aeration b) binding c) thickening
3. a) what part of an egg does lecithin come from?
b) Why is it used in mayonnaise?
4. Describe 3 ways you can reduce the risk of getting salmonella.
5. Why are fried eggs less healthy than boiled eggs?