Antioxidants
Mar 28, 2015
Antioxidants
Oxidation of food
Oxidation reactions can occur when food is exposed to oxygen in the air.
Foods containing fats or oils are at the greatest risk of oxidation.
Foods rich in fats and oils
When fats react with oxygen they are broken down, causing:
deterioration of flavour (rancidity)
loss of colour
loss of nutritional value
a health risk from toxic oxidation products.
Effects of oxidation on food
Fat breaking down
Oxygen
FatFat
Fat molecules
Fat
CH2
CH2
CH2
CH2
CH2
COO
CH2
CH3
CHH
H
CH2
CH2
CH2
CH2
CH
COO
CHCH3
C
C
O
H
H
CH2
CH2
CH2
CH2
CH2
CO
CH2
CH3
R CH2CH2CH2CH CH CH3
Radicals attack near the double bond(NB ‘R’ represents the remainder of the fat molecule)
Antioxidants
Antioxidants are chemicals that are added to food to prevent the food from ‘going off’.
An antioxidant is a substance that slows down or prevents the oxidation of another chemical.
Oxidative damage
Oxidation reactions can produce free radicals.
A free radical is a highly reactive species containing an unpaired electron.
Free radicals can damage food by removal of an electron.
Antioxidant molecules ‘mop up’ free radicals to protect the foodstuff.
Damaging free radical
Electrontransferred
Antioxidant Antioxidant converted to a stable free radical
Neutralised free radical
Radical now in a stable pair
How does an antioxidant cancel out a free radical?
The antioxidant molecule donates an electron to the potentially damaging free radical.
A stable electron pair is formed, stabilising the free radical.
The antioxidant itself becomes oxidised (loses an electron).
Types of antioxidants
Antioxidant Natural/synthetic E number Types of food
Vitamin C
(ascorbic acid)
Natural E300 Fruits, jams, vegetables
Vitamin E
(tocopherols)
Natural E306 Oils, meat pies, soya beans
Butylated hydroxyanisole
(BHA)
Synthetic E320 Margarine, cheese, crisps
Antioxidants in action
Oxidation occurs when the apple is left exposed to air
The apple is protected when dipped in orange juice containing the antioxidant vitamin C
Vitamin C (ascorbic acid)
The antioxidant vitamin C can act as a reducing agent (electron donor), preventing oxidation (electron loss) from the foodstuff.
C6H8O6 C6H6O6 + 2H+ + 2e-
Ascorbic acid Dehydroascorbic acid