Food tests

Question 1

How to prepare a food sample

Answer 1

1) Get a piece of food and break it 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 solid bits of food

Question 2

Test for REDUCING sugar (bread) PRACTICAL

Answer 2

Benedict’s test
1) prepare a food sample and transfer 5cm^3 to a test tube
2) prepare a water bath so that it’s set to 75 degrees
3) add some benedict’s solution to the test tube using a pipette
4) Place the test tube in the water bath using a test tube holder and leave it there for 5 min, make sure the tube is pointing away from you
5) If the food sample contains reducing sugar, the solution in the test tube will change from normal blue to green, yellow or brick red colour - depends on how much sugar is in the food

Question 3

Test for starch ( pasta, rice , potatoes )

Answer 3

Iodine solution

1) Make a food sample and transfer 5cm^3 of your sample to a test tube
2) then add a few drops of iodine solution and gently shake the tube to mix the contents. If the sample contains starch, the colour of the solution will change from browny-orange to black or blue-black

Question 4

Test for proteins ( meat, cheese )

Answer 4

biuret test

1) prepare a food sample and transfer 2cm^3 to a test tube
2) Add 2cm^3 of biuret solution to the sample and mix the contents of the tube by gently shaking it
3) If the food sample contains proteins, the solution will change from blue to purple.
No protein = solution remain blue

Question 5

Test for lipids ( olive oil, milk )

Answer 5

Sudan III stain solution

1) Prepare of sample of the food you’re testing , Transfer about 5 cm^3 into a test tube
2) use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake the tube
3) Sudan III stain solution stains lipids. If sample contains lipids, mixture will separate out into 2 layers. The top layer will be bright red . If sample contains no lipids = mixture will not separate out into 2 layers. The top layer will not be bright red