10.3 Antioxidant Substances
Antioxidants are vital chemical substances needed by our body to slow down or stop the oxidation process. They protect body cells from damage caused by free radicals and serve as a defensive line against diseases.
Learning Objectives
- State the definition of antioxidant substances.
- Identify examples of antioxidant substances found in foods and their dietary sources.
- Describe the action of antioxidants on free radicals.
- Explain the factors affecting food oxidation such as exposure to air.
- Carry out an experiment to investigate the effects of different solutions on the oxidation of apples.
Examples and Food Sources of Antioxidants
Five major dietary antioxidants protect the body in different ways.
Short Explanation
Definition
Antioxidants are chemical substances needed by our body to slow down or to stop the oxidation process.
Antioxidants protect body cells from damage caused by free radicals and act as a defensive line against diseases. The body produces antioxidants naturally, but this production decreases with age, so we need to obtain them from food.
How antioxidants work. When an antioxidant reacts with a free radical, more stable compounds are produced. This stops the oxidation process and prevents further cell damage.
Oxidation in daily life. Fruits such as apples and bananas turn brown when left exposed to the air because they undergo oxidation.
Experiment 10.1: Effects of Different Types of Solution on the Oxidation of Apples
Investigate which solution can slow down the oxidation process on apples.
Aim
To study the effects of different types of solution on the oxidation of apples.
Problem Statement
What can slow down the oxidation process on apples?
Hypothesis
Solutions containing antioxidant can slow down the oxidation process on apples.
Variables
Manipulated: The type of solution
Responding: Colour changes on apple slices
Constant: Surrounding temperature, size of apple slice
| Materials & Apparatus | Procedure |
|---|---|
| Apple, sugar solution, lime juice, sodium bicarbonate solution, common salt solution, Petri dishes, beakers, forceps |
1. Prepare four types of solutions (sugar solution, lime juice, sodium bicarbonate solution, common salt solution). 2. Cut an apple into five equal slices. Place one slice in a Petri dish as a control. 3. Use forceps to soak each remaining apple slice into sugar solution, lime juice, sodium bicarbonate solution, and common salt solution for 1 minute. 4. Place the apple slices from the four solutions into Petri dishes and leave them exposed to air for 15 minutes. 5. Observe and compare the colour changes of the apple slices with the control slice. |
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is the primary role of antioxidant substances in the human body?
Name the antioxidant that is associated with healthy eyes and state one food source for it.
Why does a freshly cut apple slice turn brown when left on a table?
Common Mistakes
- Thinking that our body never produces antioxidants and that 100% must come from food at all stages of life. The body can produce them naturally, but production decreases as we age.
- Confusing the chemical names of vitamins: confusing Vitamin C (ascorbic acid) with Vitamin E (alpha-tocopherol).
- Assuming all cut apple slices will remain completely fresh in any liquid. Only solutions with antioxidant properties, such as lime juice, effectively prevent or slow browning caused by oxidation.
Concept Misunderstandings
Free radicals are stopped by destroying them completely.
Antioxidants react with free radicals to form more stable compounds, thereby stopping the chain of oxidation.
Beta carotene is only found in carrots.
Beta carotene is found in most red, yellow, or orange foods, including mangoes and sweet potatoes.
Summary
- Antioxidants are vital compounds that prevent or slow down oxidation by reacting with free radicals to yield stable compounds.
- Major dietary antioxidants include beta carotene, lutein, lycopene, vitamin C (ascorbic acid), and vitamin E (alpha-tocopherol).
- Exposure to air causes oxidation in foods like cut apples, but solutions with antioxidant properties can inhibit this browning.
Short Activity
A. Objective Quiz
1 Which antioxidant is also known as alpha-tocopherol and is found in palm oil and wheat germ oil?
2 What happens when an antioxidant reacts with a free radical?
B. Fill in the Blanks
3 Vitamin C is a water-soluble vitamin which is also known as acid.
4 Fruits such as apples and bananas turn brown when left exposed to the .
C. Drag and Drop: Match the Antioxidant to Its Source or Characteristic
Drag each antioxidant to its primary food source or characteristic. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match the Antioxidant to Its Source or Characteristic
Write the correct antioxidant next to each characteristic or source.
| Characteristic / Source | Antioxidant |
|---|---|
| 1. Red, yellow, or orange foods such as carrots and sweet potatoes | |
| 2. Associated with healthy eyes; found in spinach and broccoli | |
| 3. Found in fruits such as papaya, watermelon, and tomato | |
| 4. Water-soluble vitamin found in citrus fruits and berries |
Answer choices: Beta carotene • Lutein • Lycopene • Vitamin C
