Food tests

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This is a standard and popular experiment carried out in Biology classes. While there are some slight variations as to how this is performed, the basics are given below;

Benedict's solution is used to test for simple sugars in food, such as glucose. It is a clear blue solution of sodium and copper salts.

The Benedict's solution can be either bought in already prepared in standard volumes from 
educational suppliers or alternatively made up by the technician

In the presence of simple sugars, the blue solution changes color to green, yellow, and brick-red, depending on the amount of reducing sugar present (or the amount of Copper ions in solution).


Practical setup
Students should have the following supplied

  • Access to a range of foods (Some foods should prove positve as well as negative for the presence of glucose)
  • Mortar and Pestal
  • Dropper
  • Test tubes
  • Safety Glasses
  • Adhesive labels (or marker)
  • Water bath (set at ~60 - 80OC) (or this can be done using bunsen burner, tripod, heat proof mat and guaze)
  • Bottles of Benedict's reagent

Refer to CLEAPSS Recipe and Hazcards (27C, 34, 40C, 91 (2008 ed.)) for more information regarding the any Hazards and preparation of Benedict's reagentbr>

There has been discussions regarding the temperature that the water bath should be set to. In practice the higher the temperature, the faster the reaction will occur. The reaction will proceed quite happily around 40 - 60OC - albeit slowly! remember that steam from a covered hot water bath can be hazardous to the student or demonstrator if it is set at 100 OC and hot water above 60OC can also cause burns. So as part of your risk assessment the teacher should take these factors into account.

Student

  • Mix small amount of each food sample with distilled water to make a test liquid. To a test tube, add 5cm3 of liquid to be tested.
  • If testing more than one liquid, label each test tube with a marker.
  • Add 10 drops of Benedict's solution to each test tube. Carefully heat the test tubes by suspending in a hot water bath at about 60-80 degrees celsius for five minutes.
  • Note any color change. If sugar is present solution will turn green, yellow, or brick-red, depending on sugar concentration.

See also:



--Ssmith 07:57, 17 June 2008 (BST)