Food tests required practical

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"Use qualitative reagents to test for a range of carbohydrates, lipids and proteins (to include: Benedict’s test for sugars; iodine test for starch; and Biuret reagent for protein)."

Purpose

Use qualitative reagents to test for sugars, starch, lipids, and proteins.

These biological molecules make up most of an organism's biomass but are present in varying amounts in different tissues and foods.

Method

Prepare the sample by grinding the food sample using a pestle and mortar before testing.

Test for Sugars (Benedict’s Test):

Method:
- Place the sample in a boiling tube with 5 cm³ of Benedict’s reagent.
- Boil the tube in a water bath for 5 minutes.
Results:
- Negative: Stays blue.
- Positive: Turns brick red.

Test for Starch (Iodine Test):

Method:
- Add the sample to a test tube.
- Add 3 drops of iodine solution.
Results:
- Negative: Stays orange.
- Positive: Turns black.

Test for Proteins (Biuret Test):

Method:
- Place the sample in a test tube with 5 cm³ of Biuret reagent.
- Swirl the sample for 1 minute.
Results:
- Negative: Stays blue.
- Positive: Turns purple.

Test for Lipids (Ethanol Emulsion Test):

Method:
- Add the sample to a test tube with ethanol.
- Seal the tube with a bung and shake for 1 minute.
- Slowly dribble water down the side of the tube.
Results:
- Negative: Stays colourless.
- Positive: Turns milky white.

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