Carrying out Food Tests

Carrying out Food Tests

Testing for starch. Image credit fineartamerica.com

Testing for starch. Image credit fineartamerica.com

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

Materials

Benedict’s solution/Clinistix, iodine solution, Biuret’s solution/Albustix, ethanol, paper, a variety of foods to be tested, burners, suitable containers.

Methods

Testing for sugar/glucose

Benedict's solution. The test tube on the far right is testing posative for glucose

Benedict’s solution. The test tube on the far right is testing positive for glucose

  1. Place about 2 ml of food solution in a test tube and add some Benedict’s solution
  2. Heat the test tubes in a water bath
  3. Observe the colour change from green/orange to red/brown/ brick red.

Results

  • 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

  1. Drop a few drops of iodine solution on the food.
  2. Or add a food sample to a test tube containing an iodine solution

Results

  • 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

Negative (left) and Posative (right) test results for protein. Image credit wordpress.com

  1. Add a few drops of Biuret solution to the food sample.
  2. Add a food sample to a test tube containing Biuret solution

Results

  • 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.

Testing for fats

Emulsion of fats. Image credit blogspot.com

Emulsion of fats. Image credit blogspot.com

  • Place the food sample (about 2ml) into a test tube.
  • Add ethanol and shake thoroughly.

Results

  • AmĀ emulsionĀ 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.

To access more topics go to the Combined Science Notes page.

By |2017-01-17T11:15:47+00:00February 3rd, 2016|Notes, O Level Science Notes, Ordinary Level Notes|Comments Off on Carrying out Food Tests

About the Author:

He holds an Honours in Accountancy degree from the University of Zimbabwe. He is passionate about technology and its practical application in today's world.
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