Components of Food

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Components of Food

• Chemistry Project 2005-2006

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Carbohydrates

• Chemistry and Food

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What is Carbohydrates ?

• Compounds composed of carbon and water
• General formula CxH2yOy
• HO 2 1
• Divided into 3 types
• ---Monosaccharides
• ---Disaccharides
• ---Polysaccharides

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Monosaccharides

• Eg.---Glucose
• Eg.---Fructose
• Basic unit of carbohydrates
• Sweet in taste, soluble in water
• General formula C6H12O6

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Disaccharides

• Formed from 2 monosaccharides
• 2C6H12O6 -----?C12H22O11 H2O
• Condensation

Maltose
Sucrose
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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
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Glycosidic Linkage in Carbohydrates

• Bond formed between 2 monosaccharides
• Condensation---2 OH group
• Removal of H2O

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Hydrolysis of Sucrose

• Add water
• 2 simple sugars
• 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

Fehlings test
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Reducing sugar and Non-reducing sugar
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Reducing sugar and Non-reducing sugar
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Reducing sugar and Non-reducing sugar
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• Proteins

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Physical properties of proteins

• Large Molecular mass ,typically several
  thousands.
• eg. hemoglobin 64 500
• viral proteins 40 000 000
• Not truly soluble on water,but form colloidal
  suspension
• Constituent element C,H,O,N may contain S and P
• Limitless type of protein
• e.g. E.coli 800 types
• human10 000 types

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• Vary form species to species
• Therefore it determines the characteristics
  of a species
• Rarely stored in organisms except in eggs or
  seeds.

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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 non-essential,and can be synthesized
  from the essential ones.

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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 gt no of carboxyl group
• Acidic Amino Acid
• no of amino group lt no of carboxyl group

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• 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

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Polypeptide Formation

• Amino acid ?(condensation)?dipeptide?polypeptide

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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)

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Level of proteins
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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

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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
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Source of proteins

• Egg
• Milk
• Daily products
• Soya bean
• meat
• fish
• etc..

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Site for protein digestion
protein
Protease in gastric juice and pancreatic juice
Stomach duodenum
peptide
Protease in intestinal juice
Ileum
Amino Acid
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Absorption of amino acids
Amino acids
Capillaries in villi of small intestine
Liver
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Deamination
H
H2N-C-COOH
carbohydrates
H
NH2
Urea
Kidney for excretion
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Deficient disease
Kwashiorkor Symptoms of Kwashiorkor a)
Inflammation of skin b) Anaemia c) Swelling
of abdomen
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Test for Proteins

• Protein Turns Yellow Albustix paper green
• Biuret test
• Protein NaOH CuSO4 ? purple
  colouration
• (blue)
• Identification
• Paper chomatography
• 2 dimensioned 3 dimenstioned

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Fats and Oils!!!
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Foods containing Fat and Oils
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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 in water, soluble in organic solvents.
• They are mainly composed of C, H, O but with a
  very low proportion of oxygen in the molecules.

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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.

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Triglycerides
Glycerol
A fatty acid
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Synthesis of Triglycerides
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Microscopic views of fat cells
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A more colourful one
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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.

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Hydrolytic and Oxidative Rancidity

• Fats and Oils develop an unpleasant smell if they
  are kept for too long.
• They are liable to spoilage that produces an
  off odour and a flavour described as rancidity.
• Rancidity
• -gt (1) Hydrolytic (2) Oxidative
• -gt Both of which release foul smelling aldehydes
  and carboxylic acids.

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Hydrolytic rancidity

• Presence of moisture in oils, which hydrolyzes
  the glyceride molecules into propane-1,2,3-triol
  and free carboxylic acids.

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• 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.
• At room temperature, hydrolysis proceeds rapidly
  so that butter soon turns rancid.
• So, to duel with, butter is usually covered and
  refrigerated.

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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.

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Autoxidation
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Hydroperoxide

• It is flavourless and odourless
• It easily decomposes to form highly reactive
  hydroperoxide free radicals

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Autoxidation

• Can be contolled, But not be eliminated
• Can be slow down by antioxidants.
• Examples
• butylated hydroxyanisole (BHA)
• butylated hydroxytoluene (BHT)
• carotene (Pro-Vitamin A)
• Vitamin E

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Hydrolysis of Fats and oils

• Hydrolysis is a chemical process in which a
  molecule is cleaved into two parts by the
  addition of a molecule of water.
• Fats can be hydrolysed into carboxylic acids and
  glycerol in an alkaline medium (NaOH).
• It is a reversible reaction.

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Saponification
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Hardening of unsaturated fat

• An unsaturated fat is a fat in which there is one
  or more double bond between carbon atoms of the
  fatty acid chain.
• Such fat molecules are monounsaturated if each
  contains one double bond, and polyunsaturated if
  each contain more than one.
• Unsaturated fat cannot pack together closely,
  because of their bent structure. As a result,
  unsaturated oils exist as a liquid at room
  temperature.

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Saturation of fatty acid
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Hydrogenation

• Hydrogenation is a chemical reaction which can
  convert an oil to a semisolid fat by adding
  hydrogen to some of the carboxylic acid CC
  double bond , thus decreasing the degree of
  unsaturation.
• As a result , they can pack together closer and
  has a higher melting point .
• It is an important reaction to produce margarine.
• Soft spread margarine are prepared by the
  catalytic partial hydrogenation of vegetable oil .

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Catalytic Hydrogenation

• Margarine
• An unsaturated fats
• Solid forms of vegetable oil
• Widely used as a substitute for butter
• It is healthier than butter. (Why?)
• Use your brain to think
• Examples
• Corn oil
• Soy bean oil
• Cottonseed oil

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Iodine value

• Iodine value is used to measure the degree of
  unsaturation in fats and oils.
• It is determined by reacting fats or oils with
  excess iodine which adds on across the double
  bonds in the carboxylic acid side chains .
• The degree of unsaturation is defined as the
  number of grams of iodine needed to react with
  100 grams of fats/oils.
• The greater the value is , the greater the degree
  of unsaturation in the fat or oil.

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Energy Source

• The energy yield of lipids is more than twice
  those of carbohydrates and proteins, as shown in
  the below table.
• On average, around 20-30 of the daily energy
  requirement of the human body comes from
  oxidation of lipids

Approximate amount of energy released on complete oxidation(kg g-1)
Carbohydrates 17
Proteins 17
Lipids 38
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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

• They provide much more energy per gramme than
  carbohydrates and proteins.
• 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.
• They can be stored in the animal body in almost
  unlimited amount.

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Component of cell membrane

• 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.
• 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.

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Regulatory components

• 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.
• Vitamin D, which regulates the absorption of
  calcium inside the intestine, is derived from
  cholesterol.

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Component of digestive juice

• 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.

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Heat insulation

• Being a poor heat conductor, fats effectively
  reduce heat loss from the bodies of many animals,
  such as human beings, polar bears and penguins.

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Protection

• 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.

Oils on BunBun's face has protective function.
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Cell Membrance
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Credits

• Ngo Yu Hin
• Chung Man Chuen
• Fung Ho On
• Yim Pui Kin
• Yeung Sheung Yai
• Chan Kai Hung