2. Functions of FoodFunctions of Food
• to maintain life
• to supply energy & give warmth
– carbohydrates
– fats
– proteins
• for growth and repair
– Proteins
• keep healthy & help to fight against disease

3. • elements : C, H, O
– ratio of H : O
= 2 : 1
• monosaccharides
– C6H12O6
– all are sweet & soluble in water
– all are Reducing Sugars
– include Glucose, Fructose & Galactose
CarbohydratesCarbohydrates

4. disaccharides (from 2 monosaccharides)
– C12H22O11
– all are sweet & soluble in water
– Maltose ( 2 glucose molecules )
– Sucrose ( glucose + fructose)
(non-reducing sugar)
– Lactose ( glucose + galactose)
CarbohydratesCarbohydrates
surcosesurcose

5. CarbohydratesCarbohydrates
• polysaccharides (NOT sugar)
• for energy storage
– starch (store in plants)
glycogen (store in animals)
• Hydrolysis:
Polysaccharide +H2O
 Disaccharides +H2O
 Monosaccharides

6. main source of energy
cellulose:
- fibrous material of Plant Cell Wall
- dietary fibre: stimulates Peristalsis
excess carbohydrates
- stored as glycogen in liver & muscle
- stored as fats under skin
Functions of CarbohydratesFunctions of Carbohydrates

7. Test for Reducing Sugars
(Benedict’s Test)

8. Is there any colour change in
tubes A and B ?
Ans: Only the mixture in tube
A has a colour change.
A B
glucose
solution +
Benedict’s
solution
distilled
water +
Benedict’s
solution
water
bath

9. What is the sequence of
change when there is a colour
change ?
Ans: The blue solution changes
first to green, then to a
yellow coloration and
eventually a brick-red
precipitate is produced.
A B
glucose
solution +
Benedict’s
solution
distilled
water +
Benedict’s
solution
water
bath

10. Test for Starch
(Iodine Test)

11. What is the final colour in
tube A ?
Ans: The solution in tube A
changes from brown
to blue black.
iodine solution
starch
solution
distilled
water
A B

12. What is the purpose of
setting up tube B ?
Ans: To act as a control.
iodine solution
starch
solution
distilled
water
A B

13. ProteinsProteins
• elements: C, H, O, N,
sometimes S, P
• components : amino acids
forms dipeptides & polypeptides
• Condensation:
Amino acids –H2O  Dipeptides
–H2O  Polypeptide

14. Proteins
• are compounds of carbon, hydrogen, oxygen,
nitrogen and sometimes sulphur, phosphorus
• amino acids:
– unit of proteins
– about 20 different types
– essential and non-essential types

15. An amino acid molecules
H2N
amino group
COOH
carboxyl group
C
R
H

16. The condensation and hydrolysis of a
polypeptide
5
1 4
3
2
1 2 3 4 5
hydrolysiscondensation

17. Condensation of two amino acid to form a
dipeptide
H2N C
R1
H
C
O
OH H
N
H
C
H
R2
COOH
H2N C
R1
H
O
H
C
H
R2
COOHC---N
H2O

18. cannot be stored
- excess proteins are deaminated by liver
~ to Urea which will be excreted away by
Kidney
~ to Carbohydrates (Glycogen) which will
be stored in Liver
ProteinsProteins

19. Functions of ProteinsFunctions of Proteins
• for growth and repair of body cells
(as structural components (cell
membrane and cytoplasm) of cells)
• to produce hormones and
enzymes and antibodies
• to give energy
• for making Haemoglobin in blood
• for making Antibodies

20. Deficiency disease of proteins
Kwashiorkor

21. Test for Proteins
(Biuret Test)

22. Test for proteins / Biuret test
egg white solution
1 cm3
NaOH solution
Put CuSO2 solution drop by
drop, and shake the mixture
after addition of each drop
Positive result: purple colour

23. What colour changes in
tubes A and B ?
Ans: Mixture in tube A
changes from blue
to purple while
mixture in tube B
remains blue
without any change.
copper sulphate solution
egg white +
sodium
hydroxide
solution
water +
sodium
hydroxide
solution
A B

24. Lipids ( fats & oils )Lipids ( fats & oils )
• elements : C, H, O
• components of 1 lipid molecule:
1 glycerol + 3 fatty acids
• insoluble in water
• soluble in organic solvent

25. Functions of LipidsFunctions of Lipids
give energy
component of cell membrane
form fatty tissues under skin
> to store energy
> acts as insulator to keep warm
to transport fat-soluble vitamins (A, D, E, K)

26. Spot Test for Fat

27. Which substance, oil or water,
leaves a permanent
translucent spot on the filter
paper ?
Ans: Oil.

28. Emulsion Test for Fat

29. Which test tube has an emulsion formed ?
Ans: Test tube A.
2 drops of
cooking oil
2 cm3
of
alcohol
2 cm3
of
distilled
water
after shaking to
form a clear
solution
shake and then
allow to stand emulsion
oil
water
shake and then
allow to stand
shaking
2 drops of
cooking oil
2 cm3
of
distilled
water
2 cm3
of
distilled
water
A
B

30. What happens to the other tube ?
Ans: The mixture separates into two layers because
fats do not dissolve in water.
2 drops of
cooking oil
2 cm3
of
alcohol
2 cm3
of
distilled
water
after shaking to
form a clear
solution
shake and then
allow to stand emulsion
oil
water
shake and then
allow to stand
shaking
2 drops of
cooking oil
2 cm3
of
distilled
water
2 cm3
of
distilled
water
A
B

31. VitaminsVitamins
• no energy value
• essential for small amount to
maintain good health
• water soluble vitamins
( B, C )
• fat soluble vitamins
( A, D, E, K )
excessive of some vitamins may
be harmful

32. Vitamin AVitamin A
 formed in the body from Carrotene
(a yellow pigment in carrots)
 destroyed at high temperature
essential for forming visual purple
(maintain dim light vision)

33. Vitamin CVitamin C
 Destroyed after prolonged cooking
 Necessary for wounds-healing
Vitamin DVitamin D
 Formed in Skin from Ultraviolet Light
 Help to regulate Ca & P metabolism

34. Detection of Vitamin C in Lemon
Juice by using DCPIP

35. What colour change has
occurred ?
Ans: The blue DCPIP
decolourizes.
syringe
lemon juice
DCPIP solution

36. What conclusion can you draw ?
Ans: Lemon juice contains
vitamin C which
decolourizes blue DCPIP.
syringe
lemon juice
DCPIP solution

37. Vitamin Sources
Deficiency
Disease
A
Egg yolk, milk,
cheese, carrot,
green
vegetables
Night blindness
C
Fresh fruits &
green
vegetables
Scurvy
D
Cod liver oil
& egg yolk
Rickets

38. Food TestsFood Tests
Substances Test
Original
Colour
Positive Result
Reducing
Sugar
Benedict’s Blue Orange ppt
Starch Iodine Brown Blue-black
Protein Biuret Blue Violet
Fats/Oils Spot ---
Translucent
spot
Fats/Oils Emulsion Clear Milky emulsion
Vitamin C DCPIP Blue
Colourless
(decolourize)

39. Mineral SaltsMineral Salts
regulate body metabolism
essential for healthy growth
necessary for construction of certain
tissues
needed in small amount
include Ca, S, K, Na, Mg, Fe, I

40. Mineral(s) Sources Functions
Deficiency
Disease
Calcium &
Phosphorus
Cheese,
milk,
vegetables
Making bones &
teeth
Important for
blood clotting &
muscle
contraction
Rickets
Iron
Liver, eggs,
beef, green
leafy
vegetables
Structural
component of
Haemoglobin
Anaemia

41. Dietary FibreDietary Fibre
mainly cellulose
indigestible material for human
give bulk to food & stimulate peristalsis 
prevent Constipation
lack of dietary fibre: Large Intestine Cancer
sources: wholemeal cereals, unpolished
rice, fresh vegetables & fruits

42. Balanced DietBalanced Diet
• have enough food to supply enough
– energy
• carbohydrates, fats, proteins
– body building materials
• proteins
– substances to maintain health
• vitamins, minerals, water &
dietary fibres
• malnutrition : not having balanced
diets for long time

43. Energy Contents in FoodEnergy Contents in Food
• Calorimeter is used to measure the
amount of energy contained in a
particular type of food
• Carbohydrate (17kJ/g)
• Protein (18kJ/g)
• Fat (39kJ/g)

44. Factors affecting energyFactors affecting energy
requirementrequirement
• Sex
• Age
• Occupation
• Physical Activities
• Stage of individual
(pregnancy, breast-feeding)

45. Measure the Energy
Value of Food

46. boiling tube
water
burning
peanut
thermometer
Explain why the energy value
of the peanut is lower than
those from standard tables.
Ans: Because there are a
number of inaccuracies
associated with this
method due to
incomplete combustion
and heat loss.

47. Basal Metabolic Rate (BMR)Basal Metabolic Rate (BMR)
minimum amount of energy needed by an
individual lying awake in bed to maintain
breathing, body temperature & heartbeat
varies from one individual to another
daily energy requirement > basal
metabolic rate

48. ~~ ENDEND ~~