Chapter 5: Food Requirements in Humans

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Functions 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

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Carbohydrates

• 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

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Carbohydrates

• disaccharides (from 2 monosaccharides)
• C12H22O11
• all are sweet soluble in water

• Maltose ( 2 glucose molecules )
• Sucrose ( glucose fructose)
• (non-reducing sugar)
• Lactose ( glucose galactose)

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Carbohydrates

• polysaccharides (NOT sugar)
• for energy storage
• starch (store in plants)glycogen (store in
  animals)
• Hydrolysis
  Polysaccharide H2O
  ? Disaccharides H2O
  ? Monosaccharides

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Functions of Carbohydrates

• 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

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Investigation 5.1
Test for Reducing Sugars (Benedicts Test)
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Is there any colour change in tubes A and B ?
Ans Only the mixture in tube A has a colour
change.
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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.
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Investigation 5.2
Test for Starch (Iodine Test)
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What is the final colour in tube A ?
Ans The solution in tube A changes from brown to
blue black.
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What is the purpose of setting up tube B ?
Ans To act as a control.
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Proteins

• elements C, H, O, N,
  sometimes S, P
• components amino acidsforms dipeptides
  polypeptides
• Condensation
• Amino acids H2O ? Dipeptides
• H2O ? Polypeptide

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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

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An amino acid molecules
R
COOH carboxyl group
C
H2N amino group
H
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The condensation and hydrolysis of a polypeptide
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1
2
5
3
hydrolysis
condensation
1
2
3
4
5
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Condensation of two amino acid to form a dipeptide
O
R1
H
H
C
H2N
C
N
C
COOH
OH H
H
R2
H2O
R1
H
O
C
H2N
C
COOH
C---N
H
H
R2
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Proteins

• 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
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Functions 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

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Deficiency disease of proteins

• Kwashiorkor

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Investigation 5.3
Test for Proteins (Biuret
Test)
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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
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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.
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Lipids ( fats oils )

• elements C, H, O
• components of 1 lipid molecule
• 1 glycerol 3 fatty acids
• insoluble in water
• soluble in organic solvent

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Functions of Lipids

• give energy
• component of cell membrane
• form fatty tissues under skin
• gt to store energy
• gt acts as insulator to keep warm
• to transport fat-soluble vitamins (A, D, E, K)

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Investigation 5.4
Spot Test for Fat
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Which substance, oil or water, leaves a permanent
translucent spot on the filter paper ?
Ans Oil.
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Investigation 5.5
Emulsion Test for Fat
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Which test tube has an emulsion formed ?
Ans Test tube A.
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What happens to the other tube ?
Ans The mixture separates into two layers
because fats do not dissolve in water.
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Vitamins

• 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

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Vitamin 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)

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Vitamin C

• Destroyed after prolonged cooking

• Necessary for wounds-healing

Vitamin D

• Formed in Skin from Ultraviolet Light

• Help to regulate Ca P metabolism

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Investigation 5.6
Detection of Vitamin C in Lemon Juice by using
DCPIP
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What colour change has occurred ?
Ans The blue DCPIP decolourizes.
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What conclusion can you draw ?
Ans Lemon juice contains vitamin C which
decolourizes blue DCPIP.
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Food Tests
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Mineral 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

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Dietary 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

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Balanced 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

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Energy 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)

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Factors affecting energy requirement

• Sex
• Age
• Occupation
• Physical Activities
• Stage of individual(pregnancy, breast-feeding)

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Investigation 5.8
Measure the Energy Value of Food
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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.
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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 gt basal metabolic rate

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