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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
~ ~
END END ~~