Tuesday 12 May 2015

Digestion: How do enzymes breakdown food?

Digestion begins in the mouth, you might know that we chew our food to make it small but there is something else that happens in our mouths that helps breakdown food further.  This thing is an enzyme known as AMYLASE.


Amylase is an enzyme that breaks down starch.   Depending upon the amount of reducing sugar present, it can be from light yellow-green to almost brick red in colour after heating the solution in a boiling water bath. It doesn't detect non-reducing sugars.

Chew on a bit of bread for a minute or so.  Don’t swallow.  The taste of it changes.  Can you tell what your saliva, well the amylase in your saliva, turns the starches into? 


It’s true, you can turn the starch in your bread to sugar just by chewing it and keeping it in your mouth.
This happens because of an enzyme called Amylase.  Amylase catalyses (catalyses means causes a reaction) the hydrolysis (hydrolysis means the chemical breakdown of a compound due to a reaction with water) of starch into sugar. 

Amylase is present in human saliva and in some other mammals and this is where the chemical process of digestion begins.

Foods like bread, potato and rice become sweeter as we chew them as they are high in starch and this starch is turned into sugar by the amylase as we have already discovered in our first science experiment. 

The pancreas and the salivary gland make amylase to hydrolyse dietary starch.  This is then converted into glucose by other enzymes to supply the body with energy.

The pancreas produces lots of digestive enzymes.  Enzymes are imperative (that means absolutely necessary) in the digestive process.  Each enzyme has a specific job.  Like a jigsaw, they will only fit and breakdown the substances they were made to break down:
  • An Amylase enzyme will only fit into a carbohydrate, a starch and break it down into sugar
  • A protease, like pepsin, will only fit into a protein and break it down into amino acids
  • A lipase, lipids, will only fit into fat and break it down into fatty acids or glycerol

We can do an experiment that proves that starch I turned into sugar, as it happens in the mouth as we mix food with saliva.  To do this you will need: 

  • Corn flour
  • Amylase
  • Iodine - here's how to make your own: click here
  • Water
  • 2 test tubes with lids, one for the iodine and one for the solution we will make up.
  • 6 Petri dishes or a clear plastic bag.
  • 2 pipettes
  • Optional: Benedict’s solution – if you use this you will also need an extra pipette.


Add ¼ teaspoon of Amylase and ¼ teaspoon of corn flour ( the corn flour is the starch) to one of your test  tubes. 


Fill the test tube with water, tap water is fine, so it is 1/3 full.


Put a lid on your test tube and give it a gentle shake


Test for starch.

Hypothesise about what will happen when you mix the solution you have made with iodine.

In one your petri dishes (or on a small area of your plastic bag if you don’t have petri dishes) put a drop of the amylase and starch solution on using one of your pipettes.  Always use this first pipette only for the amylase and starch solution.

Then, with the second pipette, drop the smallest drop of iodine onto your drop in you petri dish (or on your plastic bag).

It goes black!   This means starch is present.


Leave the solution for 5 minutes.  Repeat STEP FOUR – don’t forget to your hypothesis.


Leave for another 5 minutes and repeat STEP FOUR.  Do this another 4 times.

On the last test you should notice that when you mix the iodine in with the solution it’s no longer black but it’s yellow.  You should also notice that each time you test the solution the colours will go from black, to brown, to orange and then yellow.  This means that the starch has all been turned into sugar.

If you have the Benedict’s reagent solution you could test to see if simple sugars are present in the solution.  If there is sugar present the solution will go a green to yellow colour, if you heat your solution in a bath of boiling water the colour will turn to a brick red colour.
Benedict’s reagent solution does not detect not-reducing sugars, but will detect the simple sugars form in the reaction of Amylase and starch.

I hope you enjoyed this experiment.  If you want to learn more about digestion why not click on the image bellow and go to a fun project to learn about the rest of our digestive tract...



  1. The initial step of assimilation happens in the mouth. Delectably sweet starches - like cake, treats, bread, and pasta- - begin their breakdown here. Next, the sustenance is transported to the stomach through the throat, a long, limit strong tube that extends from your mouth to your stomach. Once the nourishment gets to the stomach, chemicals and compounds begin to destroy the sustenance. From the stomach, the mushed up nourishment, or chyme, goes into the small digestive tract. Here's the place the activity happens. Sustenance is further separated through substance assimilation and supplements from nourishment are consumed into the blood that flows through our bodies. Extra organs like the pancreas, liver, and gallbladder over here as well. Next, the digestive organ retains water and sends the waste to the rectum for transfer.

  2. As a child I liked to make some experiments with some materials and it was not always successful.

  3. If your child like makiking some experiments you have to halp him and take part in it with them.

  4. Wow! It's amazing! You should Start Writing A Book about your experiments. Kids would love it!