Interpret Chemical Tests on Food

Would you be able to run a marathon? That's roughly 26 miles! That's tiring just thinking of it!

Marathon runners often have a meal high in carbohydrates the night before a race to provide them with the slow-releasing energy they need to run.

 

 

Food provides us with energy. Our body releases this energy using respiration. This energy is used to allow muscles to contract, for example, allowing us to run that marathon! Respiration also allows us to grow and helps keep all the parts of our body working properly.   

 

It's important for us to know then, exactly what's in our foods so that we can ensure we are getting the balanced diet that our bodies need. Below are a few tests that can be used to show if fats, proteins, starch or sugars are present in the foods we eat.

 

The Chemical Tests for Carbohydrates

 

 

There are two types of carbohydrate. One is the complex carbohydrate starch and the other is the simple carbohydrate, glucose (a type of sugar).

 

The test for starch uses a chemical called iodine solution. When added to something containing starch, iodine solution will turn from a orange-red/brown colour to a blue/black colour. 

 

 

The test for glucose uses a chemical called Benedict's reagent/solution. This blue coloured solution is named after a scientist called Stanley Rossiter Benedict. When added to something containing glucose, Benedict’s solution will turn from blue to orange/brick red.  

 

 

The Chemical Test for Proteins

The test for protein uses a chemical called Biuret solution.  When added to something containing protein, Biuret solution will turn from a blue colour to a purple colour.  

 

 

The Chemical Test for Fats 

The test for fats is not quite as simple as the tests for carbohydrates and protein.

 

Firstly, add the food to be tested to a small amount of ethanol (pure alcohol) and let it dissolve. The solution may need to be heated in order for it to dissolve fully. We must not use a Bunsen burner or a naked flame, because ethanol is highly flammable - therefore a water bath should be used. 

 

Next, the dissolved food solution is added to a test tube of water. If the solution remains colourless, there are no fats present. If a layer of cloudy white emulsion forms at the top, then it's a positive result - there is fat in this type of food.

 

 

In this activity, we will interpret the results of different food tests to see what nutrients they contain.

 

Let's go!