Resource,%20Materials%20and%20Environment

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Resource, Materials and Environment

• Lesson 2 Food Chemistry

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Food Components

• Protein Amino acids, Peptide and Polypetide
• Carbohydrates
• Fats and oils
• Food Additives
• Food Production

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Proteins

• proteins are essential parts of all living
  organisms

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Amino acids

• Building blocks for protein
• Properties of amino acids
• Differentiation of amino acids, techniques
• Chromatography and electrophoresis

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Peptide bond
Peptide group

• Dehydration synthesis (condensation) reaction
  forming a peptide group
• Peptides are synthesized by coupling the carboxyl
  group or C-terminus of one amino acid to the
  amino group or N-terminus of another.

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Properties of amino acids

• Due to the co-existence of the NH3and the COO-,
  amino acids exhibit amphoteric behaviour, for
  instance alanine reacts both with acids and bases

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• There are twenty standard amino acids proteins by
  living cells. Different sequencing of amino acids
  results in different type of proteins.

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Properties of amino acids

• Amino Acid is slightly acidic. For alanine, the
  following reaction occurs in pure water

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Properties of amino acids

• Isoelectric point
• The pH at which an amino acid carries no net
  electric charge, this quantity can be determined
  by an analytical technique called electrophoresis

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Isoelectric Point
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Separation of amino acids

• Electrophoresis
• Based on the mobility of ions in an electric
  field.

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Separation of amino acids

• Thin Layer Chromatography (TLC)
• Useful for separating organic compounds.
• Stationary Phase
• A static phase, usually a solid or a liquid
  adsorbed on a solid supported

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Separation of amino acids

• Mobile phase
• A dynamic phase, the components to be separated
  is carried through the stationary phase by the
  mobile phase

Mobile phase Stationary phase name abbreviation
Gas Liquid Gas-liquid GLC
Liquid Solid Liquid-solid LSC
Gas Solid Gas-solid GSC
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Joining amino acids Formation of Peptide

• Condensation reaction through elimination of
  water molecules
• CH3CH(NH2)COOH alanine
• H2NCH2COOH glycine ?
• CH3CH(NH2)OC-NHCH2COOHH2O or
• H2NCH2OC-NHCH(COOH)CH3H2O
• Which one yields more?

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Peptide bond

• Partial double bond character
• C-N bond length(1.32 A? ) is shorter
• R groups are arranged trans to each other to
  prevent repulsion
• Rotation is restricted about the C-N bond

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Peptide bond
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Peptide bond
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Peptide bond

• Unit, Residue Each amino acid in the peptide
• Dipetide form from two units
• Tripeptide formed from three units
• Polypeptide any difference from a protein?

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Structure of protein

• Primary structure
• Secondary structure
• Long chains of amino acids will commonly fold or
  curl into a regular repeating structure.
• Structure is a result of hydrogen bonding between
  amino acids within the protein.

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Protein as a polymer

• Resonance structures of the peptide bond that
  links individual amino acids to form a protein
  polymer.
• A protein is polypeptides more than about 50
  amino acids long.

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Structure of protein molecule
Different reconstructed illustrations of protein
molecule
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Primary structure of Protein

• Here is an example sequence of amino acids in a
  protein.
• It also shows the abbreviations commonly used.

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Secondary Structure

• Common secondary structures are
• a-helix
• ß-pleated sheet
• Secondary structure adds new properties to a
  protein like strength, flexibility

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a-helix

• High strength
• Low solubility in water

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Proteins (a-helix example)
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ß-pleated sheet

• Silk fibroin
• Stack like corrugated cardboard for extra strength

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ß-pleated sheet (Secondary structure)

• Held together by hydrogen bonding between
  adjacent sheets of protein

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Effect of temperature and pH on proteins

• Both will alter the 3-D shape of a protein if you
  go beyond a normal range.
• Disorganized protein will no longer act as
  intended denatured.
• They will clump together coagulate.
• Example frying in an egg, reason for HCl in
  stomach

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An example of Tertiary Structure Collagen

• About one third of all protein in humans
• Provide strength to bones, tendon, skin, blood
  vessels.
• Form triple helix-tropocollagen

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Collagen and Vitamin C

• Major use of Vitamin C is for making collagen
• Scurvy disease from lack of Vitamin C results
  in skin lesions, bleeding gums and fragile blood
  vessels.

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Protein hormone examples
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Carbohydrates

• Carbo (carbon) hydrate (water)
• Made up of C,H,O moleucles
• Can be classified into monosaccharides,
  disaccharides and polysaccharides
• Carbohydrates are the most abundant biological
  molecules, and fill numerous roles in living
  things, such as
• storage and transport of energy (starch,
  glycogen)
• structural components (cellulose in plants,
  chitin in animals).

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Carbohydrates- monosaccharides (I)

• Better known as simple sugar
• Has reducing power
• Common examples are glucose, galactose and
  fructose
• Source of energy in our body

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Carbohydrates- monosaccharides (II)
Glucose molecule
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Disaccharides (I)

• Form by dehydrating reaction between two
  molecules of monosaccharides
• Has the general formula of C12H22O11

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Disaccharides (II)
Sucrose (table sugar) (glucosefructose)
Lactose (sugar in milk) (glucosegalactose)
Maltose (glucoseglucose)
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Polysaccharides

• Polysaccharides have a general formula of
  Cn(H2O)n-1 where n is usually a large number
  between 200 and 2500. The general formula can
  also be represented as (C6H10O5)n where
  n100-3000.
• Examples include starch, glycogen, cellulose,
  chitin.

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• Starch in flour and bread is an example of
  polysaccharides

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Fats and fatty acids
Butter
Oil
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Fats and fatty acids

• Fats and oils provide our body with energy and
  essential fatty acids (carboxylic acids)
• R,R,R are hydrocarbon chains
• Esters of propane-1,2,3-triol and fatty acids

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Hydrolysis of fats
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Reaction with sodium hydroxide
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Fatty Acid Structure

• Long chain monocarboxylic acids
• CH3(CH2)nCOOH Size rangeC12-C24
• Always an even number of carbon
• Saturated no double bonds
• Unsaturated one or more double bonds

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Hydrogenation of unsaturated fatty acids

• Hydrogenation
• RCHCHCH2CH2COOH(H2,Ni)?RCH2CH2CH2CH2COOHUsed
  to convert unsaturated vegetable oils to margarine

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Unsaturated fatty acids an example

• Elcosanoids
• All are unsaturated
• All have twenty carbons
• Some are Essential Fatty Acids
• Cant be produced by the body
• E.g. linolenic acid and linoleic acids

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Iodine value

• Unsaturated fat is considered desirable in the
  diet
• A quantitative measure of the degree of
  unsaturation in fats and oils
• Based on the reaction
• -CHCH- I-I ?-CHI-CHI-
• Defined as the number of grams of iodine that
  reacts with 100 grams of fats/oils

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The higher the value is, the greater the
degree Of unsaturation in the fat or oil.
Fats / Oils Iodine Values
Animal fats Butter ?? 25-30
Dripping ?? 35-65
???? Lard ?? 45-65
Vegetable oils Coconut oil ??? 8-10
?????? Cotton seed oil and soya oil 80-140
Ground-nut oil ??? 85-105
??? Olive oil ??? 80-90
Almond oil ??? 90-110
Corn oil ??? 115-130
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Some common fatty acids
Common IUPAC Name MP Formula
Lauric??? n-dodecanoic 44 C11H23COOH
Palmitic??? n-hexadecanoic 63 C15H31COOH
Stearic??? n-octadecanoic 70 C17H35COOH
Palmitoleic???? Cis-9-hexadexenoic 0 C15H29COOH
Oleic?? Cis-9-octadecenoic 16 C17H33COOH
Linoleic??? Cis,cis,9,12-octadecadienoic 5 C17H31COOH
Presence of double bonds reduces melting point.
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Food Additives

• Chemical added to preserve and/or improve the
  appearance of food
• Several Classes
• Colourings, Antioxidants, Flavour Enhancers,
  Preservatives, Sweeteners, Emulsifiers,
  stabilizers, and thickeners, and etc.

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Principles of food preservation

• Removal of moisture
• Altering temperature
• Changing pH value
• Use of osmotic process
• Use of chemical additives

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Some Food Preservation Techniques
Irradiation Expose food to ionizing radiation
Drying and Dehydration Dried in the sun or in special ovens or freeze driers
Refrigeration In chilling, kept at 0-4oC
Canning Cooked under pressure in hermetically sealed container
Salting Treated with salt or strong salt solution
Pickling in vinegar Kept in vinegar
Use of food additives Substances which control micro-organisms and chemical spoilage
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Some classes of food additives
Preservatives Prevent microbial growth and spoilage
Antioxidants Prevent rancidity of fats and oils
Emulsifier, stabilisers, and thickener Give texture, blend, smoothness and other consistencies stabilize oil-water mixtures.
Anticaking agents Keep food fast flowing, prevent caking in humid weather
Humectants Retain moistures
Leavening agents Make food light in the texture
Bleaches Confer white colour to food
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Some common food additives
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Some common flavourings
Flavour Food Additive
Ginger Ginger oil
Grape Methyl anthranilate
Lemon Citral
Orange Orange oil
Pear Amyl butyrate
Spearmint Carvone
Vanilla Ethyl vanillin
Spicy Ethyl cinnamate
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E numbers of food additives
Type of additive E number
Colourings Most begin with 1
Preservatives Most begin with 2
Flavourings Not numbered
Antioxidants 300-321
Emulsifiers and stabilisers E322 and some numbers between E400 and E495
Acids, bases and buffers Most begin with 5
Sweeteners Most begin with 4 or 6
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Flavour enhancer

• MSG (Monosodium-L-glutamate monohydrate)
• Chemically isolated by a Japanese in 1908
• Excess intake linked to with the symptoms known
  as Chinese Restaurant Syndrome.

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The need to preserve food
Food additives
Principles of food preservation
Different functions
Principle of BHA/BHT as antioxidant
Possible menace
Inhibition of microbial growth
Killing of micro-organisms
Ratardation of chemical changes
Monitoring and legislation
Common food preservation techniques
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Regulations on Color Additives in US

• Food and Drug Administration (FDA) responsible
  for regulation all man-made color additives
• Color additive certification as approval process
  assures the safety, quality, consistency and
  strength.
• Example Caramel used in sauces, soft drinks, and
  baked foods.

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Regulations on Food Additives

• All foods have to be labeled with ingredients.
• In some countries, such as US, all foods should
  be labeled with specific food additives.
• MSG has been given green light as a food additive.

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Wikipedia links

• Food chemistry
• Carbohydrates
• Protein
• Lipid
• Enzymne
• Vitamins
• Dietary minerals