Food testing (bio molecules topic)

Question 1

What steps are in involved in the process of making a food solution?

Answer 1

Grind the food with distilled water in a mortar and pestle to make a paste

Then add more water to get a mixture

Filter the mixture through filter paper to remove solid objects and get a solution called a filtrate

Question 2

Describe the steps involved in testing for starch

Answer 2

Add 3cm cubed of the food solution to a test tube along with 1 cm cubed of iodine solution

If there is starch present the solution will turn blue-black

If starch is not present the solution will remain orange (the colour of the iodine solution)

Question 3

Describe the steps involved in testing for proteins (peptide bonds)

Answer 3

Add 3cm cubed of the food solution to a test tube along with 3cm cubed of dilute sodium hydroxide solution, also known as biuret

Then add 10 drops of dilute copper sulfate solution

If protein is present the solution will turn purple or lilac

If protein is not present the solution will remain blue

Question 4

Describe the steps involved in testing for lipids

Answer 4

Add 3cm cubed of the food solution to a test tube with 3cm cubed of ethanol and water

Shake the solution

If lipids are present then the solution form a cloudy white emulsion

If lipids are not present then the solution will stay clear

Question 5

Describe the steps involved in testing for reducing sugars

Answer 5

Add 3 cm cubed of the food solution to a test tube with 3 cm cubed of benedict’s solution

Place the test tube in a water bath between 80-100 degrees C for at least 5 minutes

If reducing sugars are not present then the solution will remain blue

If reducing sugars are present then a small amount of red precipitate will form

Depending on the concentration of the sugar the solution will turn:
green, yellow, orange, brick red from weakest to strongest

Question 6

Describe the steps involved in testing for non-reducing sugars

Answer 6

Perform the benedict’s test for reducing sugars on the unknown solution and not down any colour changes

Add 3cm cubed of the unknown mixture to a test tube with 3cm cubed dilute hydrochloric acid

Gently boil the solution for 5 minutes in a water bath at 80-100 degrees C

Then slowly add drops of an alkaline to neutralise the solution or make it alkaline

Add 3 drops of benedict’s solution and put in a water bath for 5 minutes at between 80-100 degrees C

Note down any colour changes

If non-reducing sugars are present then the solution will turn red or orange

If there is a high concentration of reducing sugars then the test is not possible

Question 7

What colours are present in a food test for starch?

Answer 7

Present: Blue-black

Absent: Orange

Question 8

What colours are present in a food test for proteins? (peptide bonds)

Answer 8

Present: Purple or lilac

Absent: Blue

Question 9

What colours are present in a food test for lipids?

Answer 9

Present: Cloudy white emulsion

Absent: Clear

Question 10

What colours are present in a food test for reducing sugars?

Answer 10

Present: Red precipitate. Solution can turn green, yellow, orange or brick-red

Absent: Blue

Question 11

What colours are present in a food test for non-reducing sugars?

Answer 11

Present: Red or orange

Depends on results of the first benedict’s test as if there is a high concentration of reducing sugars the test is not possible