10.3 Antioxidant Substances

Definition and Examples of Antioxidant Substances

An antioxidant is a chemical compound required by the body to slow down or stop oxidation.

Protects body cells from damage by free radicals.
Acts as a line of defence against the risk of certain diseases.
The body produces antioxidants, but this ability decreases with age; antioxidants must therefore be obtained through food.

Antioxidant	Food sources and description
Beta carotene	Red, yellow or orange foods: carrots, mangoes and sweet potatoes
Lutein	Associated with healthy eyes; abundant in green leafy vegetables such as spinach, cabbage and broccoli
Lycopene	Papaya, guava, watermelon, tomato, apricot, grapefruit and orange
Vitamin C	Water-soluble vitamin also known as ascorbic acid; citrus fruits, spinach, broccoli, kiwi fruit, strawberries, cranberries, cabbage, green peppers and cereals
Vitamin E	Also known as alpha-tocopherol; palm oil, wheat germ oil, corn oil, soybean oil, apricots, broccoli, legumes and mangoes

Action of Antioxidants on Free Radicals

Antioxidants can be obtained from chemical synthesis or natural plants.
When an antioxidant reacts with a free radical, a more stable compound is formed.
Formation of the stable compound stops oxidation.

Factors Affecting Food Oxidation

Food exposed to air undergoes oxidation.
Fruits such as apples and bananas turn brown when exposed to air.
A solution containing an antioxidant slows the oxidation of an apple.

Experiment 10.1: Effect of Different Solutions on Apple Oxidation

Aim: To study the effect of different types of solutions on the oxidation of apples.

Problem statement: How can the oxidation of an apple be slowed down?

Hypothesis: A solution containing an antioxidant can slow down the oxidation of an apple.

Variables:

Manipulated: Type of solution.
Responding: Colour change of the apple slice.
Constant: Surrounding temperature and size of apple slice.

Materials: Apple, sugar solution, lime juice, sodium bicarbonate solution and common salt solution.

Apparatus: Petri dishes, beakers and forceps.

Procedure:

Prepare sugar solution, lime juice, sodium bicarbonate solution and common salt solution.
Cut one apple into five equal slices. Place one slice in a Petri dish as the control.
Using forceps, soak each remaining slice separately in one of the four solutions.
After 1 minute, place the four soaked slices in Petri dishes and expose them to air for 15 minutes.
Compare their colour changes with the control slice that was not soaked in any solution.

Observation table:

Type of solution	Colour change of apple slice
Sugar solution	Record after 15 minutes
Lime juice	Record after 15 minutes
Sodium bicarbonate solution	Record after 15 minutes
Common salt solution	Record after 15 minutes

Inference: Browning occurs when the cut apple is oxidised after exposure to air. A substance that prevents or reduces browning slows oxidation.

Conclusion: A solution containing an antioxidant slows down the oxidation of an apple; the hypothesis is accepted if its apple slice browns more slowly than the control.