Resource, Materials and Environment

1. Resource, Materials and Environment Lesson 2: Food Chemistry

2. Food Components • Protein: Amino acids, Peptide and Polypetide • Carbohydrates • Fats and oils • Food Additives • Food Production

3. Proteins • proteins are essential parts of all living organisms

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

5. 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.

6. 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;

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

8. Properties of amino acids • Amino Acid is slightly acidic. For alanine, the following reaction occurs in pure water:

9. 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

10. Isoelectric Point

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

12. 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

13. Separation of amino acids Mobile phase A dynamic phase, the components to be separated is carried through the stationary phase by the mobile phase

14. 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?

15. 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

16. Peptide bond

17. Peptide bond

18. 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?

19. 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.

20. 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.

21. Structure of protein molecule Different reconstructed illustrations of protein molecule

22. Primary structure of Protein Here is an example sequence of amino acids in a protein. It also shows the abbreviations commonly used.

23. Secondary Structure • Common secondary structures are: a-helix β-pleated sheet • Secondary structure adds new properties to a protein like strength, flexibility…

24. a-helix • High strength • Low solubility in water

25. Proteins (a-helix example)

26. β-pleated sheet • Silk fibroin • Stack like corrugated cardboard for extra strength

27. β-pleated sheet (Secondary structure) • Held together by hydrogen bonding between adjacent sheets of protein

28. 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

29. 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

30. 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.

31. Protein hormone examples

32. 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).

33. Carbohydrates- monosaccharides (I) • Better known as “simple sugar” • Has reducing power • Common examples are glucose, galactose and fructose • Source of energy in our body

34. Carbohydrates- monosaccharides (II) Glucose molecule

35. Disaccharides (I) • Form by dehydrating reaction between two molecules of monosaccharides • Has the general formula of C12H22O11

36. Disaccharides (II) Sucrose (table sugar) (glucose+fructose) Lactose (sugar in milk) (glucose+galactose) Maltose (glucose+glucose)

37. 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.

38. Starch in flour and bread is an example of polysaccharides

39. Fats and fatty acids Oil Butter

40. 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

41. Hydrolysis of fats

42. Reaction with sodium hydroxide

43. 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

44. Hydrogenation of unsaturated fatty acids • Hydrogenation RCH=CHCH2CH2COOH—(H2,Ni)→RCH2CH2CH2CH2COOHUsed to convert unsaturated vegetable oils to margarine

45. 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

46. 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

47. The higher the value is, the greater the degree Of unsaturation in the fat or oil.

48. Some common fatty acids Presence of double bonds reduces melting point.

49. 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.

50. Principles of food preservation • Removal of moisture • Altering temperature • Changing pH value • Use of osmotic process • Use of chemical additives