Components of Food
Chemistry Project 2005-2006
Carbohydrates
Chemistry and Food
What is Carbohydrates ?
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Compounds composed of carbon and water
General formula CxH2yOy
H:O = 2 : 1
Divided into 3 types
---Monosaccharides
---Disaccharides
---Polysaccharides
Monosaccharides
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Eg.---Glucose
Eg.---Fructose
Basic unit of carbohydrates
Sweet in taste, soluble in
water
General formula C6H12O6
Disaccharides
Formed from 2 monosaccharides
 2C6H12O6 -----C12H22O11 + H2O
 Condensation

Maltose
Sucrose
Polysaccharides
Condensation polymer of
monosaccharides
 nC6H12O6--(C6H10O5)n + n(H2O)
 Condensation
 Example:
 ---Starch
 ---Cellulose
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Open Chain and Ring Structures
of Glucose and Fructose
Glycosidic Linkage in
Carbohydrates
Bond formed between 2
monosaccharides
 Condensation---2 OH group
 Removal of H2O
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Hydrolysis of Sucrose
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Add water
2 simple sugars
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Dilute mineral acids
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Hydrolysis of starch (1)
With enzymes
 To maltose
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Hydrolysis of Starch (2)
Boiled with dilute H2SO4
 To glucose
 (C6H10O5)n + nH2O-- nC6H12O6
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Reducing and Non-reducing
Sugars
Reduces basic solution of Cu2+(aq) or
Ag+(aq)
 Sugar converted to acid
 Aldehyde group
 Keto group
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Fehling’s test
Reducing sugar and Non-reducing sug
Reducing sugar and Non-reducing sugar
Reducing sugar and Non-reducing sugar
Proteins
Physical properties of proteins

Large Molecular mass ,typically several thousands.
eg. hemoglobin :64 500
viral proteins :40 000 000
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Not truly soluble on water,but form colloidal
suspension
Constituent element: C,H,O,N may contain S and P
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Limitless type of protein
e.g. E.coli :800 types
human:10 000 types

Vary form species to species
Therefore it determines the characteristics of a
species

Rarely stored in organisms except in eggs or
seeds.
Structure of amino acids
 A group of over a hundred members
 The commonest are the 20 essential ones,which cannot be
synthesized by our bodies.While the rest are nonessential,and can be synthesized from the essential ones.
Zwitterions formation
Basic amino group : -NH2
Acidic carboxyl group : -COOH
Neutral Amino Acid:
no of amino group = no of carboxyl group
Basic Amino Acid:
no of amino group > no of carboxyl group
Acidic Amino Acid:
no of amino group < no of carboxyl group
Dipolar : with both positive and negative
pole
Form zwitterions
 Soluble in water but not in organic solvent
 Non-volatile, crystalline organic
compound with high melting point
 Amphoteric : with both acidic and alkaline
properties
Buffer
Biological significance : Constant Ph for
enzymatic reaction
Polypeptide Formation
Amino acid (condensation)dipeptidepolypeptide
Structure of polypeptide
 Three dimension
 Four types of bonding:
a) disulphide bond
b) hydrogen bond
c) hydrophobic interaction
d) ionic bond (broken by alternation in pH)
Level of proteins
Denaturation
 Change in shape but not the sequence
 Factors:
- Heat
- Acid
- Alkali
- high electropositive eg.Ag+ Hg +
- high electronegative eg. CN- organic solvent
- Mechanical force
Function of proteins
1.cytoskeleton : cytoplasm consists of a network of fibrous
proteins
2. Membrane protein
3. Raw material for growth
4. Formation of enzymes, hormones, antibodies
5. Fibrous proteins for support and protection
6. Osmotic balance and buffering
7. Energy source
Source of proteins
 Egg
 Milk
 Daily products
 Soya bean
 meat
 fish
etc…..
Site for protein digestion
protein
Stomach & duodenum
Protease in gastric juice and
pancreatic juice
peptide
Protease in intestinal juice
Ileum
Amino Acid
Absorption of amino acids
Amino acids
Capillaries in villi of small intestine
Liver
Deamination
H
H2N-C-COOH
H
NH2
Urea
Kidney for excretion
carbohydrates
Deficient disease
Kwashiorkor
Symptoms of Kwashiorkor:
a) Inflammation of skin
b) Anaemia
c) Swelling of abdomen
Test for Proteins
1) Protein Turns Yellow Albustix paper green
2) Biuret test:
Protein + NaOH + CuSO4  purple colouration
(blue)
Identification
Paper chomatography
2 dimensioned
3 dimenstioned
Fats and Oils!!!
Foods containing Fat and Oils:
What are fats and oils?
 Fats
and Oils are different lipids.
 Lipids
are rather diverse class of organic
compounds of organic compounds that include
triglycerides, phospholipids, steriods, etc.
 insoluble
 They
in water, soluble in organic solvents.
are mainly composed of C, H, O but with a
very low proportion of oxygen in the molecules.
Structure of fats and oils:
 Most
natural fats and oils are mixed glycerides.
 Glycerides
are esters formed from propane-1,2,3-triol
(glycerol) and a mixture of different long chain
carboxylic acids.
 The
carboxylic acids(fatty acids) making up fats and
oils are usually unbranched, having 14 to 18 carbons.
 There
are three ester groups per glycerol and the three
R groups are usually different, fats and oils are often
called triglycerides.
Triglycerides
Glycerol
A fatty acid
Synthesis of Triglycerides
Microscopic views of fat cells
A more colourful one
Animal fats and Vegetable oils:
 Fats
and Oils are found in animals and plants.
 Animal
fats, such as lard and butter, are
composed of glycerides rich in heavy chain,
saturated fatty acids, Therefore they are solids
at room temperatures.
 Vegetable
oils are liquids because of their high
content of glycerides composed of light chain
unsaturated fatty acids.
Hydrolytic and Oxidative Rancidity
 Fats
and Oils develop an unpleasant smell if they
are kept for too long.
are liable to spoilage that produces an ‘off’
odour and a flavour described as rancidity.
 They
 Rancidity
:
->(1) Hydrolytic (2) Oxidative
->Both of which release foul smelling aldehydes
and carboxylic acids.
Hydrolytic rancidity

Presence of moisture in oils, which hydrolyzes the glyceride
molecules into propane-1,2,3-triol and free carboxylic acids.
 This
reaction is speeded up in the presence of certain
micro-organisms or in the presence of some enzymes.
 Over
a period of time, more molecules of carboxylic
acids are liberated which may be volatile and have
extremely unpleasant odours and flavours.
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At room temperature, hydrolysis proceeds rapidly so that butter soon turns
rancid.
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So, to duel with, butter is usually covered and refrigerated.
Oxidative Rancidity
 Oxidative
spoilage occurs when fats/oils are exposed to
air and undergo oxidation.
 It
results in the production of flavours such as ‘tallowy’,
A taste of fatty according to “yahoo dictionary”.
 Fats
and oils with a high degree of unsaturation are
more susceptible to oxidation.
 The
oxidation has a free radical mechanism and is
accelerated by trace metals, light and free radical
initiators.
Autoxidation
H
C
H
H
H
C
C
C
H
H
segment of carboxylic acid in fat/oil
O2 in the air
Autoxidation
H
H
H
H
C
C
C
C
HO
O
H
hydroperoxide
Hydroperoxide
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It is flavourless and odourless
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It easily decomposes to form highly reactive
hydroperoxide free radicals
Hydroperoxide
Hydroperoxide
free radical
cleavage of
double bonds
Aldehydes,ketones
and carboxylic acids
Autoxidation
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Can be contolled, But not be eliminated
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Can be slow down by antioxidants.
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Examples :
butylated hydroxyanisole (BHA)
butylated hydroxytoluene (BHT)
carotene (Pro-Vitamin A)
Vitamin E
Hydrolysis of Fats and oils
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Hydrolysis is a chemical process in which a molecule is
cleaved into two parts by the addition of a molecule of
water.
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Fats can be hydrolysed into carboxylic acids and
glycerol in an alkaline medium (NaOH).
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It is a reversible reaction.
Saponification
Hardening of unsaturated fat
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An unsaturated fat is a fat in which there is one or
more double bond between carbon atoms of the
fatty acid chain.
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Such fat molecules are monounsaturated if each
contains one double bond, and polyunsaturated if
each contain more than one.
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Unsaturated fat cannot pack together closely,
because of their bent structure. As a result,
unsaturated oils exist as a liquid at room
temperature.
Saturation of fatty acid
Hydrogenation
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Hydrogenation is a chemical reaction which can convert
an oil to a semisolid fat by adding hydrogen to some of
the carboxylic acid C=C double bond , thus decreasing
the degree of unsaturation.
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As a result , they can pack together closer and has a
higher melting point .
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It is an important reaction to produce margarine.
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Soft spread margarine are prepared by the catalytic
partial hydrogenation of vegetable oil .
Catalytic Hydrogenation
Margarine:
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An unsaturated fats
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Solid forms of vegetable oil
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Widely used as a substitute for butter
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It is healthier than butter. (Why?)
Use your brain to think…
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Examples:
Corn oil
Soy bean oil
Cottonseed oil
Iodine value:
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Iodine value is used to measure the degree of
unsaturation in fats and oils.
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It is determined by reacting fats or oils with excess
iodine which adds on across the double bonds in the
carboxylic acid side chains .
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The degree of unsaturation is defined as the number
of grams of iodine needed to react with 100 grams of
fats/oils.
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The greater the value is , the greater the degree of
unsaturation in the fat or oil.
Energy Source
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The energy yield of lipids is more than twice those of
carbohydrates and proteins, as shown in the below
table.
Approximate amount of energy
released on complete oxidation(kg
g-1)
Carbohydrates
Proteins
Lipids
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17
17
38
On average, around 20-30% of the daily energy
requirement of the human body comes from oxidation
of lipids
Energy Reserve
Triglycerides are common energy reserve in the
adipose tissue of animals. They are an excellent storage
form of energy because of the followings:
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They provide much more energy per
gramme than carbohydrates and
proteins.
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They are insoluble in water so that
they do not diffuse out of the cells
and do not upset the osmotic
balance of the cells.
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They can be stored in the animal
body in almost unlimited amount.
Component of cell membrane
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The cell membrane is formed by two layers (bilayers) of
phospholipids, with the lipophilic hydrocarbon ends
facing each other and the hydrophilic phosphate ends
pointing outward to the aqueous environment.
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Cholesterol in the cell membrane helps to limit the
leakage of small molecules, and hold the hydrocarbon
chains of the phospholipids together but not changing
them into a solid form.
Regulatory components
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Cholesterol is also the precursor for the synthesis of
steroid hormones. Some of them are sex hormones
that stimulate the development and maintenance of
secondary sexual characteristics.
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Vitamin D, which regulates the absorption of calcium
inside the intestine, is derived from cholesterol.
Component of digestive juice
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Bile salts are made in the liver with cholesterol as a raw
materials. They emulsify dietary lipids into small oil
droplets which increase the surface area for the
enzymes to work.
Heat insulation
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Being a poor heat conductor, fats effectively reduce heat
loss from the bodies of many animals, such as human
beings, polar bears and penguins.
Protection
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Fats, being soft, light and
shock-absorbent, protect many
internal organs such as the
kidneys and the eyeball from
the mechanical injury by
cushioning them.
Cell Membrance
Credits
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Ngo Yu Hin
Chung Man Chuen
Fung Ho On
Yim Pui Kin
Yeung Sheung Yai
Chan Kai Hung