Starter c) Antioxidants Learning intention - PowerPoint Presentation

Slide1

Starter

c) Antioxidants

Learning intention

Learn about the chemistry of the antioxidant molecules which prevent oxidation reactions in foods from taking place.

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.

Oxidation of Fats

Fats and oils, or foods containing them, are the most likely to have problems with oxidation. Fats react with oxygen and even if a food has a very low fat content it may still need the addition of an antioxidant. They are commonly used in:

vegetable oil

snacks (extruded)

animal fat

meat, fish, poultry

margarine

dairy products

mayonnaise / salad dressing

baked products

potato products (instant mashed potato)

http://www.understandingfoodadditives.org

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

As the fat decomposes and reacts with oxygen, chemicals called peroxides are produced. These change into the substances characteristic of the smell and soapy flavour of a rancid fat.

Antioxidants prevent the formation of peroxides and so slow the process of the food 'going off'. Some antioxidants react with oxygen itself and so prevent the formation of peroxides.

Air-tight packaging, using inert gases like nitrogen, vacuum packing and refrigeration can all be used to delay the oxidation process. However, these can still be inefficient and adding antioxidants can be an effective way of extending the shelf life of a product.

http://www.understandingfoodadditives.org

Fat breaking down

Oxygen

Fat

Fat

Fat molecules

Fat

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

Electron

transferred

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).

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.

C

6

H

8

O

6

C

6

H

6

O

6

  +  2H

+

  +  2e

-

Ascorbic acid

Dehydroascorbic acid

Antioxidants and health benefits

There may be health benefits from the use of antioxidants. Oxidation reactions in the body could be linked to the build-up of fatty deposits that cause blockages in arteries that can cause heart attacks. Antioxidants may be important in preventing this and there could also be a link with the prevention of certain cancers, arthritis and other conditions. The picture is not yet clear and a great deal of research needs to be undertaken.

http://www.understandingfoodadditives.org

Do antioxidants help us live longer?

Studies involving 230.000 men and women across the UK have shown that there is no convincing proof that antioxidants have any effect on how long people can live. However 40% of women and 30% of men are reportedly taking these supplements and spending over £333 million on them per year.

Impact of antioxidants on health

The imbalance between free radicals and antioxidants can lead to disease and ill health. The 4 main non-enzymatic antioxidants

metalonin

, α-tocopherol (Vitamin E), ascorbic acid (Vitamin C) and β-carotene (precursor for Vitamin A) can be found in a range of foods in our diet. However medical opinions are divided as regards the impact these antioxidants have our on general health.

Free radicals in living cells

Free radicals are present in all living cell and are a part of the cell processes. However excessive free radicals in our cells can attack the cell membranes (the outer coat of the cell). This attack causes cell and tissue damage.

Radicals can also break strands of DNA (the genetic material in the cell). Some of the chemicals known to cause cancer, do so by forming free radicals.

Melatonin

This is a hormone which helps to regulate sleep in our bodies. This compound can be termed as a terminal or suicidal antioxidant as once it has removed the free radicals it has to be replaced.

α-tocopherol

This is a form of vitamin E and can be found in vegetable oil, nuts and seeds. It has been suggested that it is good for the skin.

Ascorbic Acid

This is also known as Vitamin C and is commonly found in fruits and vegetables. It is one of the essential vitamins and the human body is unable to synthesize it. It can be easily oxidised and acts as a hydroxyl or superoxide anion radical scavenger.

β-carotene

This is a precursor to vitamin A. It is a highly red-orange pigment found in plants and fruits. In particular it gives carrots their orange colour. It helps human cells to absorb vitamin A.