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Principal components of food

Principal components of food. Principal components. Proteins Carbohydrates Fats and oils. Proteins. Function – maintains the structure and proper functioning of all living organisms. Structure – a polymer formed from about 20 amino acids by peptide linkage. COOH. COOH. COOH. H. H.

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Principal components of food

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  1. Principal components of food

  2. Principal components • Proteins • Carbohydrates • Fats and oils

  3. Proteins • Function – maintains the structure and proper functioning of all living organisms. • Structure – a polymer formed from about 20 amino acids by peptide linkage.

  4. COOH COOH COOH H H H H2N C H2N H2N C C CH3 H CH2COOH 2-Aminopropanoic acid (Alanine) Aminobutanoic acid (Aspartic acid) Aminoethanoic acid (Glycine) Some amino acids

  5. H R H R’ H OH N CH C N CH C OH H O O -H2O H R H R’ N CH C N CH C Peptide linkage O O Peptide linkage

  6. Hydrolysis of proteins • Breaks the peptide linkages in a protein molecule • The composition of the protein molecule may be deduced by using paper chromatography

  7. acid H R H R’ N CH C N CH C H R H R’ O H N CH C N CH C OH O O O Hydrolysis of proteins

  8. Past paper questions • 2001 6c • 2001 6d • 2000 7b

  9. Carbohydrates • Function – provide energy • Formula – Cx H2yOy • Monosaccharides C6H12O6 (glucose, fructose) • Disaccharide C12H22O11 (sucrose, maltose) • Polysaccharides (C6H10O5)n (starch, cellulose)

  10. H H H H H H C O C* C* C* C* H C OH OH OH OH OH Stereoisomers of C6H12O6 4 chiral carbons 24 = 16 stereoisomers

  11. Glucose

  12. Glucose • Open chain (acyclic form) • Two Ring forms (cyclic form) • M.p. 146oC , 150oC • Optical rotations • +112o , +19o +52.7o

  13. Fructose

  14. Reducing sugars

  15. Reducing sugars

  16. Disaccharides

  17. Maltose

  18. Maltose

  19. Sucrose

  20. Polysaccharides • Carbohydrate polymers • Storage polysaccharides • Energy storage – starch and glycogen • Structural polysaccharides • Use to provide protective walls to cells - cellulose

  21. Starch

  22. Cellulose

  23. H+ glucose fructose Hydrolysis of sucrose • Sucrose, like all disaccharides, is hydrolysed by dilute mineral acids to two monosaccharides, glucose and fructose • C12H22O11 + H2O  C6H12O6 + C6H12O6 • The reaction can be effected by enzyme

  24. Hydrolysis of starch • A solution of starch can be hydrolysed in the presence of an enzyme to a disaccharide, maltose. • 2(C6H10O5)n +nH2O  nC12H22O11(maltose) • It starch is boiled with dilute sulphuric acid, it is hydrolyzed to a monosaccharide, glucose. (C6H10O5)n +nH2O  nC6H12O6

  25. Past paper questions • 2001 7c • 2000 6c • 1998 7b

  26. Fats and oils

  27. Triglyceride

  28. Fatty acids

  29. Fatty acid

  30. Fatty acid

  31. Hardening of vegetable oil • Unsaturated oils usually have a lower melting point and exist as a liquid. • Hydrogenation of some of the C=C bonds converts to solid fats. • E.g. Margarine

  32. Hydrolysis of fats and oils • Fats and oils are hydrolysed into carboxylic acid and glycerol in human body. • The substances are then used as fuel, or used in building cell membranes and fatty tissues. • In laboratory, hydrolysis can be carried out in an alkaline medium (i.e. saponification)

  33. Iodine value • Unsaturated fat is considered desirable in our diet. • Iodine value is defined as the number of grams of iodine that reacts with 100 grams of fats/oils.

  34. Rancidity • Rancidity is caused by reactions of fats / oils which release foul smelling aldehydes and fatty acids. • Two types: • Hydrolytic rancidity • Oxidative rancidity

  35. Hydrolytic rancidity • Occurs as a result of hydrolysis of glyceride molecules to glyerol and free carboxylic acids by the presence of moisture in the oils. • E.g. Frying of chips in oil at high temp. • The reaction is speeded up in the presence of certain micro-organisms or enzymes.

  36. Oxidative rancidity • Occurs when fats/oils are exposed to air and undergo oxidation. • Fats/oils have a high degree of unsaturation are more susceptible to oxidation. • The oxidation is a free radical mechanism and is accelerated by trace metals, light and free radical initiators.

  37. Past paper questions • 2000 6a • 1999 7d

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