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