Testing for Starch , Protein and Lipids.

First stage of food tests

Food grinded up with small amount of distilled water in mortar and pestle.

Once food is a paste, we add more distilled water and stir the mixture

Second stage of food tests

We filter our mixture to remove solid food particles, and our test is carried out on the filtrate ( the food solution passed through the filter)

What is the test for starch

First we place 3cm³ of food solution into test tube

Then add 1cm³ of solution containing iodine and potassium iodide.

In presence of starch, iodine turns blue-black, in absence of starch the iodine solution remains orange

What is test for protein

First we place 3cm³ of food solution into test tube

Add 3cm³ of dilute sodium hydroxide solution and mix, then add ten drops of dilute copper (II) sulfate solution and mix again

If protein present, solution turns purple / lilac, if protein absent it remains blue

How are lipids tested

Food mixture is not filtered, as lipids can stick to filter paper

First we place 3cm³ of food solution into test tube

Then add 3cm³ of ethanol and 3cm³ of water, then shake solution

If lipids present, white cloudy emulsion will form , if solution stays clear, then lipids are not present.