Food tests (Required Practical)

Question 1

What are the steps to carry out chemical tests for carbohydrates proteins and lipids (fats)

Answer 1

1. Take a food sample and grind this will distilled water using a moter and pestle to make a paste
2. Transfer this paste to a beaker and add more distilled water and stir so the chemicals in the food dissolve in the water
3. Filter the solution to remove suspended food particles
4. place 2 cm cubed of the food solution into the test tube

Question 2

How do you test for starch

Answer 2

Few drops of iodine which is orange

place 2 cm cubed of the food solution into the test tube

if starch is present the iodine solution will turn blue black

if no starch is present then the solution will stay orange

Question 3

how do you test for sugars

Answer 3

10 drops of Benedict solution which is blue

place 2 cm cubed of the food solution into the test tube

put the test tube into a beaker and half fill the beaker with hot water from a kettle

leave for 5 mins

if sugar presence the Benedict will change color e.g Green solution = small amount of sugar
Yellow solution = more amount of sugar
Brick red solution = lots of sugar

only works on certain sugars e.g glucose thees are called reducing sugars

will not work for non reducing sugars e.g sucrose

Question 4

how do you test protein

Answer 4

2 cm cubed of biuret solution blue color
place 2 cm cubed of the food solution into the test tube

if protein is present the biuret solution will turn purple/ lilac colors

Question 5

how do test for lipids

Answer 5

Do not filter the food solution as it lipids could stick to filter paper

few drops of distilled water and ethanol (highly flammable) place 2 cm cubed of the food solution into the test tube

gently shake the solution

if lipids are present then a white cloudy emulsion forms