B2 Food Tests (page 29)

Question 1

There are some clever ways to identify whay type of food molecule a sample contains, how is this done?

Answer 1

You need to prepare a food sample.

1) Get a piece of food and break it up using a pestle and mortar.

2) Transfer the ground up food to a beaker and add some distilled water.

3) Give the mixture a good stir with a glass rod to dissolve some of the food.

4) Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food.

Question 2

What would you use the Benedicts test to test?

Answer 2

to test for sugars.

Question 3

Sugars are found in all sorts of foods, give some examples?

Answer 3

sugar are found in biscuits, cereal and bread.

Question 4

There are two types of sugars, what are they?

Answer 4

non-reducing and reducing.

Question 5

You can test for reducing sugars in foods using what test?

Answer 5

Benedict’s test.

Question 6

Explain the process of the Benedict’s test?

Answer 6

1) Prepare a food sample and transfer 5cm³ to a test tube.

2) Prepare a water bath so that it’s set to 75°C.

3) Add some Benedict’s solution to the test tube (about 10 drops), using a pipette.

4) Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes. Make sure the tube is pointing away from you.

5) If the food sample contains a reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow or brick-red - it depends on how much sugar is in the food.

(in general blue to blue-green or yellow-green is negative, yellowish to bright yellow is a moderate positive, and bright orange is a very strong positive of reducing sugars

Question 7

What do the colours represent on the Benedict sugar test?

Answer 7

Benedicts solution is blue, but if simple carbohydrates are present, it will change colour green/yellow if the amount is low and red if it is high.

Question 8

What do you use Iodine solution to test?

Answer 8

starch.

Question 9

Give some food samples for starch?

Answer 9

foods like pasta, rich and potatoes contain a lot of starch.

Question 10

What is starch?

Answer 10

Starch is a carbohydrate commonly found in nature and one of the primary sources of food energy for human beings. It is regularly eaten in the form of wheat, rice and potatoes. Itarch is one of the main categories of carbohydrates.

Question 11

What is the process test to check for starch?

Answer 11

1) Make a good saple and transfer 5cm³ of your sample to a test tube.

2) Then add a few drops of iodine solution and gently shake the tube to mis the contents.

If the sample contains starth, the colour of the solution will change from browny-orange to black or blue-black.

Question 12

What is the Biuret Test?

Answer 12

its to test for proteins.

Question 13

You can use the Biuret test to see if a type of food contains protein, what foods can be tested?

Answer 13

Meat and Cheese are protein rich and good foods to use in the test.

Question 14

What is the Process of the Biuret Test?

Answer 14

1) Prepare a sample of your food and transfer 2cm³ of your sample to a test tube.

2) Add 2cm³ of biuret solution to the sample and mix the contents of the tube by gently shaking it.

3) If the food sample contains protein, the solution will change from blue to purple. If no protein is present, the solution will stay blue.

Question 15

What is the Sundan III Test?

Answer 15

to test for Lipids.

Question 16

Lipids are found in what types of food?

Answer 16

foods such as olive oil, margarine and milk.

Question 17

What is the process to test the presence of lipids in food?

Answer 17

1) Prepare a sample of the food you’re testing (but you don’t need to filter it). Transfer about 5cm³ into a test tube.

2) Use a ppette to add 3 drops of Sundan III stain colution to the test tube and gently shake the tube.

3) Sudan III stain solution stains lipids. If the sample contains lipids, te mixture will separate out into two layers. The top layer will be bright red. If no lipids are present, no separate red layer will form at the top of the liquid.

Question 18

Name the chemical that you would use to test a sample for the presence of starch? (1 mark)

Answer 18

Iodine solution (1 mark).