2. CHEMICALS THAT MAKE UP PROTEINS
Carbon
Hydrogen
Oxygen
Phosphorus
Nitrogen
Sulphur
Functions
Growth and Maintenance
Energy – 1g of pure protein provides 17KJ (4kcal)
Formation of enzymes, antibodies and some
hormones (thyroxin)
3. SOURCES OF PROTEINS
Milk and Cheese (HBV)
Meat and Fish (HBV)
Eggs (HBV)
Bread and Cereals (LBV)
Vegetables (LBV)
Nuts (LBV)
4. PROTEIN DEFICIENCY
Kwashiorkor
Common in children after weaning
Low protein and high carbohydrate diet
Symptoms
Stunted Growth, Muscle Wasting, Bloated
abdomen, Oedema (fluid in tissues causes
swelling), causes Anaemia.
Treatment
A balanced diet – more vitamins and minerals for
PEM (protein – energy malnutrition). Lowers risk of
getting disease due to fertilisers.
5. CHEMICAL STRUCTURE
Proteins are large molecules and are built up of
long chains of units called AMINO ACIDS
There are over 80 amino acids but only around 20
are found in food protein.
Structure
Acidic Part
Alkaline
Part
6. CHEMICAL STRUCTURE
Amino acids are Amphoteric because each amino acid
contains at least one amino group (NH2) and one acidic
group (COOH) which display both base (alkaline) and
acidic properties.
500 amino acids make a protein molecule
A peptide link is formed when the amino group of one
amino acid reacts with the acidic group of an adjacent
amino acid.
Condensation Polymerisation is when a molecule of
water is eliminated during the formation of the peptide
link.
When TWO amino acids join together they form a
Dipeptide.
When long chains of amino acids join together they form
a Polypeptide.
8. THE BIOLOGICAL VALUE OF PROTEIN
Biological Value of protein is used as a measure of
protein quality.
Foods that contain all essential amino acids are of
better quality than foods that do not.
High Biological Value foods (HBV) are: Meat, Fish,
Eggs, Milk and Cheese.
Low Biological Value foods (LBV) are: Bread,
Cereals, Nuts and Pulses.
Complementation foods are proteins containing
different essential amino acids (i.e. HBV and LBV
foods) are eaten together e.g.
Beans on toast Bread and Cheese
Rice Pudding Macaroni Cheese
9. DENATURATION AND COAGULATION
Denaturation
When the physical structure of the protein is altered in
an irreversible way.
The protein becomes less soluble and more viscous
e.g. whisking egg whites
Coagulation
The hardening or setting of a protein e.g. frying an
egg
10. DENATURATION CAN BE BROUGHT BY VARIOUS
MEANS:
Action of Heat
Many proteins coagulate when heated e.g. egg
Egg white coagulates at 60 C and egg yolk
coagulates at 66 C
Denatured proteins are readily attacked by digestive
enzymes to make the food more digestible.
Presence of Acid
Milk sours due to bacteria present in milk which
ferment lactose, producing lactic acid.
The pH of milk lowers causing the milk protein to
coagulate.
11. DENATURATION CAN BE BROUGHT BY VARIOUS
MEANS:
Addition of Salt
Sodium Chloride coagulates some proteins
In cheese making, salt is added to curd to increase
firmness and suppress growth of micro-organisms.
If salt is added to cooking water used for boiling eggs,
the white will not escape as readily if the shell is
cracked.
Addition of Rennin
a.k.a. Rennet – an enzyme which coagulate protein
and use to make Junket which clots/ coagulates
milk.
Rennin is also used together with a bacterial starter
culture to form a curd in cheese manufacture.
12. DENATURATION CAN BE BROUGHT BY VARIOUS
MEANS:
Mechanical Action
During whisking of egg white causes a partial
coagulation of protein.
Protein molecules unfold and form a reinforcing
network round the air bubbles – this stabilises the
foam.
Used in food production e.g. meringues and soufflés.
13. MAILLARD REACTION
A.K.A. Non-enzymic browning
It is a browning reaction which occurs during roasting,
baking, grilling and frying of many foods.
A chemical reaction takes place between:
The amino group of a free amino acid
A free amino group on a protein chain
The carbonyl group of a reducing sugar e.g. glucose.
