ZIMSEC O Level Combined Science Notes: Carrying out Food Tests
It is important to know how much nutrients they contain
This would be useful to nutritionist and those who are health conscious
Food Testing experiments
Simple tests can be made on food to determine if they contain a particular food group e.g. proteins
Benedict’s solution/Clinistix, iodine solution, Biuret’s solution/Albustix, ethanol, paper, a variety of foods to be tested, burners, suitable containers.
Testing for sugar/glucose
Benedict’s solution. The test tube on the far right is testing positive for glucose
Place about 2 ml of food solution in a test tube and add some Benedict’s solution
Heat the test tubes in a water bath
Observe the colour change from green/orange to red/brown/ brick red.
The Benedict’s solution changes from green/orange to brick red if the food contains sugar/glucose
NB. You can also test for the presence of starch using a clinistix by dipping it into a food sample, waiting for about 30 seconds,observing the resulting colour change and comparing the result to a provided colour code.
Testing for starch
Drop a few drops of iodine solution on the food.
Or add a food sample to a test tube containing an iodine solution
The iodine solution turns blue black if starch is present.
Testing for protein
Negative (left) and Posative (right) test results for protein. Image credit wordpress.com
Add a few drops of Biuret solution to the food sample.
Add a food sample to a test tube containing Biuret solution
If the food sample contains proteins the solution will turn blue/ a darker shade of blue.
NB You can also test for the presence of proteins using an albustix by dipping it into a food solution, waiting for about 30 seconds, observe the colour change and comparing it against a provided colour code.
Place the food sample (about 2ml) into a test tube.
Add ethanol and shake thoroughly.
Am emulsion forms if fat or oil is present
NB. Alternatively a small amount the food can be smeared onto a piece of paper. And left to dry for a couple of minutes, the remaining stain is then observed. If a translucent stain forms then fat is present in the food sample being tested.
A translucent stain is one which allows light to pass but does not allow a person to see through it.