Food Tests

Question 1

What is the colour of a positive/negative Starch test, and what solution is used.

Answer 1

Pos = BLUE-BLACK COLOR
Neg = ORANGE 

Used = a few drops of Iodine Solution

Question 2

What is the colour of a positive/negative for reducing sugars/glucose test, and what solution is used.

Answer 2

Pos = BRICK RED
Neg = blue 

Used = a few drops of Benedict’s solution

Next Heat gently (10mins)

Question 3

What is the colour of a positive/negative Protein, and what solution is used.

Answer 3

Pos = VOILET/PURPLE 
Neg = BLUE 

Used = a few drops of Biuret A and Biuret B

Next Shake the test tube gently

Question 4

What is the colour of a positive/negative Fats/lipids test, and what solution is used.

Answer 4

Pos = white precipitate layer forms 
Neg = nothing occurs 

Used = few drops of water and few drops of ethanal

Question 5

What is the required practical for enzymes?

Answer 5

1. 3 test tubes: pH (amount can vary), amylase, starch
2. One drop of iodine solution into each depression of spotting tile
3. 2cm cubed of each solution into a test tube and then a water bath and wait until all have reached 30C
4. Use syringe to place 2cm cubed of of starch into the buffered pH solution
5. Then use another syringe to put 2cm cubed amylase into the starch + pH test tube
6. Immediately start the clock and leave it on throughout the test
7. After every 20 seconds add one drop of the solution to one of the depressions in the spotting tile, the iodine should turn a blue black colour
8. Do this every 20 seconds until the iodine has no change in colour ( this is when the amylase has broken down all the starch )
9. repeat the test for other pHs
10. Record your results on a table