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Resource, Materials and Environment. Lesson 2: Food Chemistry. Food Components. Protein: Amino acids, Peptide and Polypetide Carbohydrates Fats and oils Food Additives Food Production. Proteins. proteins are essential parts of all living organisms. Amino acids.

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resource materials and environment

Resource, Materials and Environment

Lesson 2: Food Chemistry

food components
Food Components
  • Protein: Amino acids, Peptide and Polypetide
  • Carbohydrates
  • Fats and oils
  • Food Additives
  • Food Production
proteins
Proteins
  • proteins are essential parts of all living organisms
amino acids
Amino acids
  • Building blocks for protein
  • Properties of amino acids
  • Differentiation of amino acids, techniques
  • Chromatography and electrophoresis
peptide bond
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.
properties of amino acids
Properties of amino acids
  • Due to the co-existence of the NH3+and the COO-, amino acids exhibit amphoteric behaviour, for instance alanine reacts both with acids and bases;
slide7
There are twenty standard amino acids proteins by living cells. Different sequencing of amino acids results in different type of proteins.
properties of amino acids8
Properties of amino acids
  • Amino Acid is slightly acidic. For alanine, the following reaction occurs in pure water:
properties of amino acids9
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

separation of amino acids
Separation of amino acids
  • Electrophoresis
  • Based on the mobility of ions in an electric field.
separation of amino acids12
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

separation of amino acids13
Separation of amino acids

Mobile phase

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

joining amino acids formation of peptide
Joining amino acids: Formation of Peptide
  • Condensation reaction through elimination of water molecules::

CH3CH(NH2)COOH alanine +

H2NCH2COOH glycine →

CH3CH(NH2)=OC-NHCH2COOH+H2O or

H2NCH2=OC-NHCH(COOH)CH3+H2O

Which one yields more?

peptide bond15
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
peptide bond18
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?
structure of protein
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.

protein as a polymer
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.
structure of protein molecule
Structure of protein molecule

Different reconstructed illustrations of protein molecule

primary structure of protein
Primary structure of Protein

Here is an example sequence of amino acids in a protein.

It also shows the abbreviations commonly used.

secondary structure
Secondary Structure
  • Common secondary structures are:

a-helix

β-pleated sheet

  • Secondary structure adds new properties to a protein like strength, flexibility…
a helix
a-helix
  • High strength
  • Low solubility in water
pleated sheet
β-pleated sheet
  • Silk fibroin
  • Stack like corrugated cardboard for extra strength
pleated sheet secondary structure
β-pleated sheet (Secondary structure)
  • Held together by hydrogen bonding between adjacent sheets of protein
effect of temperature and ph on proteins
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
an example of tertiary structure collagen
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
collagen and vitamin c
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.
carbohydrates
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).
carbohydrates monosaccharides i
Carbohydrates- monosaccharides (I)
  • Better known as “simple sugar”
  • Has reducing power
  • Common examples are glucose, galactose and fructose
  • Source of energy in our body
disaccharides i
Disaccharides (I)
  • Form by dehydrating reaction between two molecules of monosaccharides
  • Has the general formula of C12H22O11
disaccharides ii
Disaccharides (II)

Sucrose (table sugar)

(glucose+fructose)

Lactose

(sugar in milk)

(glucose+galactose)

Maltose

(glucose+glucose)

polysaccharides
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 n=100-3000.
  • Examples include starch, glycogen, cellulose, chitin.
fats and fatty acids40
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
fatty acid structure
Fatty Acid Structure
  • Long chain monocarboxylic acids

CH3(CH2)nCOOH Size range:C12-C24

Always an even number of carbon

Saturated: no double bonds

Unsaturated: one or more double bonds

hydrogenation of unsaturated fatty acids
Hydrogenation of unsaturated fatty acids
  • Hydrogenation

RCH=CHCH2CH2COOH—(H2,Ni)→RCH2CH2CH2CH2COOHUsed to convert unsaturated vegetable oils to margarine

unsaturated fatty acids an example
Unsaturated fatty acids: an example

Elcosanoids

  • All are unsaturated
  • All have twenty carbons
  • Some are Essential Fatty Acids
  • Can’t be produced by the body
  • E.g. linolenic acid and linoleic acids
iodine value
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:

-CH=CH- + I-I →-CHI-CHI-

Defined as the number of grams of iodine that reacts with 100 grams of fats/oils

slide47

The higher the value is, the greater the degree

Of unsaturation in the fat or oil.

slide48

Some common fatty acids

Presence of double bonds reduces melting point.

food additives
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.

principles of food preservation
Principles of food preservation
  • Removal of moisture
  • Altering temperature
  • Changing pH value
  • Use of osmotic process
  • Use of chemical additives
flavour enhancer
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”.
slide57

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

regulations on color additives in us
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.
regulations on food additives
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.
wikipedia links
Wikipedia links
  • Food chemistry
  • Carbohydrates
  • Protein
  • Lipid
  • Enzymne
  • Vitamins
  • Dietary minerals