1.  

2.  Explainthe differences between the
three main types of antioxidants.

3.  Anantioxidant is a substance that
delays the onset or slows the rate of
oxidation
 Antioxidants are added to foods such as
oils, fats and butter to prevent oxidative
rancidity.

4.  

5.  either preventing the loss of electrons
from fats and oils by donating electrons
of their own, thus removing reactive
free
radicals which are needed for the
propagation step.
 or
reducing the availability of transition
metal ions in solution.

6. Types of
antioxidants
Reducing Free radical Chelating
agents scavengers agents

7.  Are electron donors and they remove or
reduce the concentrations of oxygen.
 Reducing agents are oxidized in preference
to fats or oils. Rancidity of fats and oils is an
oxidation reaction, which occurs by a free-
radical mechanism, and is catalysed by
transition metal ions.
 Examples include ascorbic acid(vitamin C)
and carotenoids.

8.  Vitamin
C is readily oxidized on
exposure to air, to form
dehydroascorbic acid.

9.  Form stable and less reactive free
radicals:
ROO• +AH → ROOH + A•
 Examplesinclude BHA, BHT, TBHQ
and tocopherols.

10.  

11.  BHA, BHT, TBHQ and tocopherols (which
we will represent as AH) acts as
antioxidants as they form relatively stable
and unreactive free radicals when they lose
a hydrogen atom to the reactive free
radicals through homolytic fission.
 R+ AH → RH + A
 RO + AH → ROH + A
 ROO + AH → ROOH + A

12.  Thefree radicals produced, can also
remove free radicals in termination steps:
 R+ A → RA
 RO + A → ROA

13.  Reduce the concentration of free metal
ions in solution.
 Examples include salts of EDTA and
plant extracts (rosemary, tea, ground
mustard)
 EDTA forms especially strong
complexes with Mn(II), Cu(II), Fe(III), Pb
(II) and Co(III).

14.  A chelate is a chemical compound composed of a metal
ion and a chelating agent. A chelating agent is a
substance whose molecules can form several bonds to a
single metal ion. In other words, a chelating agent is a
polydentate ligand.
 EDTA is a versatile chelating agent. It can form four or
six bonds with a metal ion, and it forms chelates with
both transition-metal ions and main-group ions.

16. The polydentate ligand
EDTA can take the place of
six
monodentate ligands as it
has six lone
pairs available.
Metal-EDTA

17.  The removal of the free metal ion from
solution as a chelate, means that it is
not free to catalyse oxidation reactions.
 EDTA forms chelates with many metal
ions and is widely used as a food
additive.