Functions of Food to maintain life to supply energy & give warmth –carbohydrates –fats...

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

• 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

disaccharides (from 2 monosaccharides)

– C11H22O11

– all are sweet & soluble in water– Maltose ( 2 glucose molecules )– Sucrose ( glucose + fructose) (non-reducing sugar)– Lactose ( glucose + galactose)

CarbohydratesCarbohydrates

surcosesurcose

CarbohydratesCarbohydrates

• polysaccharides (NOT sugar) • for energy storage

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

• Hydrolysis: Polysaccharide +H2O

Disaccharides +H2O Monosaccharides

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 Functions of CarbohydratesCarbohydrates

Test for Reducing Sugars (Benedict’s

Test)

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

ube 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 contro

l.

iodine solution

starch solutio

n

distilled water

A B

ProteinsProteins• elements: C, H, O, N,

sometimes S, P• components : amino acids

forms dipeptides & polypeptides• Condensation: Amino acids –H2O Dipeptides –H2O Polypeptide

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

Functions of Functions of ProteinsProteins

• for growth and repair

(as structural components of cells)• to produce hormones and

enzymes• to give energy• for making Haemoglobin in blood• for making Antibodies

Test for Proteins (Biuret Test)

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

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

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)

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 oi

l

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 oi

l

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 beca

use fats do not dissolve in water.

2 drops of cooking oi

l

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 oi

l

2 cm3 of distilled water

2 cm3 of distilled water

A

B

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

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)

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

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 SourcesDeficiency

Disease

A

Egg yolk, milk, cheese, carrot, green vegetables

Night blindness

CFresh fruits &

green vegetables

Scurvy

DCod liver oil & egg yolk

Rickets

Food TestsFood 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 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

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 FibreDietary Fibre mainly cellulose indigestible material for human give bulk to food & stimulate peristalsi

s prevent Constipation lack of dietary fibre: Large Intestine Ca

ncer sources: wholemeal cereals, unpolishe

d rice, fresh vegetables & fruits

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

Energy Contents in Energy Contents in FoodFood

• 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)

Factors affecting energy Factors affecting energy requirementrequirement

• Sex• Age• Occupation• Physical Activities• Stage of individual

(pregnancy, breast-feeding)

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 n

umber of inaccuracies associated with this method due to incomplete combustion and heat loss.

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

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