biology - food tests

Question 1

how to prepare a sample of food to be tested?

Answer 1

• grind up food samples using pestle and mortar
• mix with water
• filter with funnel and filter paper

Question 2

how to test for starch in a sample?

Answer 2

• add iodine solution to the sample
• if starch is present, it turns from brown to blue/black

Question 3

how to test for the presence of a reducing sugar in a sample?

Answer 3

• add Benedict’s reagent to the sample
• if reducing sugar is present, a brick red precipitate forms. If not, the solution remains blue

Question 4

how to test for the presence of protein in a sample?

Answer 4

• add Biuret reagent (potassium hydroxide and copper II sulphate)
• shake mixture
• if protein is present, solution turns from blue to purple

Question 5

describe how to test for the presence of lipids in a sample?

Answer 5

• add ethanol to the sample
• then add water to the sample
• shake the test tube
• if lipids are present, white emulsion formed if lipid present