2.4 - Food Tests

Question 1

How do you Prepare a Food Sample? [4]

Answer 1

1 ) Break the piece of food up into small pieces.
2 ) Place the crushed food into a beaker filled with distilled water.
3 ) Stir the mixture with a glass rod until some of it dissolves.
4 ) Filter out the solution using a funnel with filter paper.

Question 2

What is the Food Test for Reducing Sugars?

Answer 2

Benedict’s Test

Question 3

What is the Method for Benedict’s Test?

Answer 3

1 ) Transfer 5cm³ of the Food Sample into a Test Tube.
2 ) Prepare a Water Bath and set it to 75°C.
3 ) Add about 10 drops of Benedict’s Solution to the Test Tube & Place it in the Water Bath for 5 Minutes.

Question 4

What Safety Precautions should you take for Benedict’s Test?

Answer 4

• Use a Test Tube Holder to Place the Test Tube into the Water Bath.
• Point the Tube Away from You and Anybody Else.

Question 5

What are the Positive & Negative Results for Benedict’s Test?

Answer 5

Positive (Reducing Sugars Present) - The Solution will Change Colour to Green, Yellow, or Brick Red.
Negative (No Reducing Sugars Present) - The Solution will stay Blue.

Question 6

What is the Food Test for Starch?

Answer 6

The Iodine Test

Question 7

What is the Method for the Iodine Test?

Answer 7

1 ) Transfer 5cm³ of the Food Sample into a Test Tube.
2 ) Add a few drops of Iodine Solution to the Sample.
3 ) Gently Shake the Test Tube.

Question 8

What are the Positive & Negative Results for the Iodine Solution Test?

Answer 8

Positive (Starch Present) - The Solution will Change Colour to Blue/Black.
Negative (No Starch Present) - The Solution will stay a Browny Orange Colour.

Question 9

What is the Food Test for Protein?

Answer 9

The Biuret Test

Question 10

What is the Method for the Biuret Test?

Answer 10

1 ) Transfer 2cm³ of the Food Sample into a Test Tube.
2 ) Add 2cm³ of Biuret Solution to the Sample.
3 ) Gently Shake the Test Tube.

Question 11

What are the Positive & Negative Results for the Biuret Test?

Answer 11

Positive (Protein Present) - The Solution will Change Colour to Pink or Purple.
Negative (No Protein Present) - The Solution will stay Blue.

Question 12

What is the Food Test for Lipids?

Answer 12

The Sudan III Test

Question 13

What is the Method for the Sudan III Test?

Answer 13

1 ) Transfer 5cm³ of the Food Sample into a Test Tube. (Does not have to be Filtered).
2 ) Add Three drops of Sudan III Stain Solution to the Sample.
3 ) Gently Shake the Test Tube.

Question 14

What are the Positive & Negative Results for the Sudan III Test?

Answer 14

Positive (Lipids Present) - A Red Layer of Lipids would be left Separated out on top.
Negative (No Lipids Present) - No Red Layer of Lipids would be Visible.