Principal components of food

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Principal components of food
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Principal components

• Proteins
• Carbohydrates
• Fats and oils

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Proteins

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

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Some amino acids
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Peptide linkage
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Hydrolysis of proteins

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

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Hydrolysis of proteins
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Past paper questions

1. 2001 6c
2. 2001 6d
3. 2000 7b

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Carbohydrates

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

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Stereoisomers of C6H12O6
4 chiral carbons 24 16 stereoisomers
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Glucose
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Glucose

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

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Fructose
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Reducing sugars
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Reducing sugars
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Disaccharides
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Maltose
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Maltose
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Sucrose
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Polysaccharides

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

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Starch
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Cellulose
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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

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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

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Past paper questions

1. 2001 7c
2. 2000 6c
3. 1998 7b

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Fats and oils
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Triglyceride
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Fatty acids
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Fatty acid
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Fatty acid
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Hardening of vegetable oil

• Unsaturated oils usually have a lower melting
  point and exist as a liquid.
• Hydrogenation of some of the CC bonds converts
  to solid fats.
• E.g. Margarine

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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)

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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.

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Fats / Oils Fats / Oils Iodine values
Animal fats Butter 25-30
Animal fats Dripping 35-65
Animal fats Lard 45-65
Vegetable oils Coconut oil 8-10
Cotton seed oil 80-140
Ground-nut oil 85-105
Olive oil 80-90
Almond oil 90-110
Corn oil 115-130
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Rancidity

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

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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.

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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.

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Past paper questions

1. 2000 6a
2. 1999 7d