practical

Question 1

how do we conduct benedicts test?
how to read the results?

Answer 1

• Add 2 cm3 of Benedict’s solution to 2 cm3 of food sample in a test-tube.
• Shake the mixture.
• Heat the contents in a boiling water bath for 2–3 minutes.
  ``
• solution remained blue; no reducing sugar
• turned from blue to green; traces of rs
• blue to yellow to orange; moderate amount of rs
• blue to red/ red precipate formed;large amount of rs

if sample is a solid food, crush it to release cell contents. crush the sample in water using a mortar and pestle, shake and pour the water into a new test tube. then add into reagent.

Question 2

how to carry out iodine test

Answer 2

• Add a few drops of iodine solution
  to a food sample.
• Expected observation: If starch is present, the iodine solution turned from brown to blue-black.

Question 3

how do we carry out an ethanol elmusion test

Answer 3

• Add 2 cm3 of ethanol to 2 cm3 of food sample to a clean test-tube.
• Shake the contents of the tube vigorously.
• Add 2 cm3 of water into the test-tube and shake the mixture.

Expected Observation: A cloudy white emulsion is formed if fats are present.

Solid food: Add ethanol to the crushed food to dissolve the nutrients, shake and decant the mixture to a new to a test-tube before adding water.

Question 4

how to carry out a biuret test

Answer 4

• Add 2 cm3 of biuret solution to 2 cm3 of food sample to a clean test tube.
• Shake well and allow the mixture to stand for five minutes.

Expected Observation: A violet solution is formed if proteins are present.

if sample is solid food, do the same steps as the benedicts test