Food Requirements

and Components

to maintain life to supply energy & give warmth

◦ carbohydrates◦ fats◦ proteins

for growth and repair◦ Proteins

keep healthy & help to fight against disease

Functions of Food

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

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)

Carbohydrates

surcose

polysaccharides (NOT sugar) for energy storage

◦starch (store in plants)glycogen (store in animals)

Hydrolysis: Polysaccharide +H2O

Disaccharides +H2O Monosaccharides

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

Functions of Carbohydrates

Test for Reducing Sugars (Benedict’s

Test)

Is there any colour change in tubes A and B ?Ans: Only the mixture

in tube A has a colour change.

A Bglucose solution

+ Benedict

’s solution

distilled water +

Benedict’s solution

water bath

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 Bglucose solution

+ Benedict

’s solution

distilled water +

Benedict’s solution

water bath

Test for Starch (Iodine

Test)

What is the final colour in tube A ?

Ans: The solution in tube A changes from brown to blue black.

iodine solution

starch solutio

n

distilled water

A B

What is the purpose of setting up tube B ?Ans: To act as a

control.

iodine solution

starch solutio

n

distilled water

A B

elements: C, H, O, N, sometimes S, P

components : amino acidsforms dipeptides & polypeptides

Condensation: Amino acids –H2O Dipeptides –H2O Polypeptide

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

Proteins

An amino acid molecules

H2Namino group

COOHcarboxyl group

C

R

H

The condensation and hydrolysis of a polypeptide

5

1 4

3

2

1 2 3 4 5

hydrolysiscondensation

Condensation of two amino acid to form a dipeptide

H2N C

R1

H

C

O

OH HN

H

C

H

R2

COOH

H2N C

R1

H

O

H

C

H

R2

COOHC---N

H2O

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

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

Functions of Proteins

Kwashiorkor

Deficiency disease of proteins

Test for Proteins (Biuret

Test)

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

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

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

Lipids ( fats & oils )

Functions 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)

Spot Test for Fat

Which substance, oil or water, leaves a permanent translucent spot on the filter paper ?

Ans: Oil.

Emulsion Test for Fat

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

oilwater

shake and then allow to

stand

shaking

2 drops of

cooking oil

2 cm3 of distilled water

2 cm3 of distilled water

A

B

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

oilwater

shake and then allow to

stand

shaking

2 drops of

cooking oil

2 cm3 of distilled water

2 cm3 of distilled water

A

B

no energy value essential for small amount

to maintain good health water soluble vitamins

( B, C ) fat soluble vitamins

( A, D, E, K )

Vitamins

excessive of some vitamins may be harmful

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)

Vitamin C Destroyed after prolonged cooking

Necessary for wounds-healing

Vitamin D Formed in Skin from Ultraviolet Light Help to regulate Ca & P metabolism

Detection of Vitamin C in Lemon Juice by using

DCPIP

What colour change has occurred ?

Ans: The blue DCPIP decolourizes.

syringe

lemon juice

DCPIP solution

What conclusion can you draw ?Ans: Lemon juice

contains vitamin C which decolourizes blue DCPIP.

syringe

lemon juice

DCPIP solution

Vitamin Sources Deficiency Disease

A

Egg yolk, milk, cheese, carrot, green vegetables

Night blindness

CFresh fruits &

green vegetables

Scurvy

DCod liver oil & egg yolk

Rickets

Food TestsSubstance

sTest

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 ClearMilky

emulsion

Vitamin C DCPIP BlueColourless

(decolourize)

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

Mineral(s) Sources FunctionsDeficiency

Disease

Calcium & Phosphor

us

Cheese, milk, vegetables

Making bones & teethImportant for blood clotting & muscle contraction

Rickets

Iron

Liver, eggs, beef, green leafy vegetables

Structural component of Haemoglobin

Anaemia

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

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

Balanced Diet

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)

Energy Contents in Food

Sex Age Occupation Physical Activities Stage of individual

(pregnancy, breast-feeding)

Factors affecting energy requirement

Measure the Energy Value of Food

boiling tubewater

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.

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

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