Objectives: To identify which carbohydrates contain reducing sugars

Background: Some sugars have a free aldehyde or ketone group which makes them capable of acting as a reducing agent. We call these sugars reducing sugars. They play an important role in developing food colors and flavors during processing. Reducing sugars produce a brick-red color when heated in the presence of Benedict’s reagent.   

Materials:

  • 1% solutions of carbohydrates (maltose, D-arabinose, sucrose, lactose, gum arabic, D-fructose, D-galactose and starch)
  • Benedicts reagent
  • Test tubes
  • Test tube rack
  • 400 ml beaker
  • Distilled water
  • 10 ml Measuring cylinder
  • Hotplate

Procedure:

  1. Prepare a boiling water bath by collecting approximately 200 ml distilled water in a 400 ml beaker and bring to boil (be sure to add 2-3 boiling stones in the water to prevent splattering
  2. While the water bath is getting ready, label test tubes from 1 through 8 or with an appropriate code corresponding to each of the 1% carbohydrate solutions
  3. Add 1 ml of each solution to the test tube
  4. Add 2 ml of Benedict’s reagent  to each of the tube and mix by gentle shaking
  5. Place each tube in the boiling water-bath for about 5 minutes
  6. Remove the tubes and place them on the test tube rack
  7. Describe and record the final color of the solution and indicate whether each sample should be classified as a reducing sugar (develop an appropriate table to clearly and effectively illustrate your findings)

Lab Questions

  1. Describe the principle of Benedict’s reagent test
  2. What makes some sugars reducing sugars while some are not?
  3. Did the reducing sugars produce different color intensities? If so, what would this indicate? 

Courtney Simons
Administrator
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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