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Different Forms of Carbohydrates and Differences Between Simple and Complex Sugars

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Author: Janice VanCleave

Carbohydrates are an important source of food energy. Carbohydrates exist in foods in different forms: monosaccharides (single sugars), disaccharides (double sugars), and polysaccharides (many sugars).

In this project, you will test for the presence of the different forms of carbohydrates. Foods containing simple sugars will be identified and the amount of sugar in each compared. You will also look at differences between complex and simple sugars.

Getting Started

Purpose: To test for the presence of monosaccharides (simple, single molecules of sugar)-in this case, glucose and fructose.

Materials

  • 2-quart (I-liter) cooking pot
  • water
  • stove
  • 2 tablespoons (30 ml) of each liquid food sample: soda, diet soda, honey, apple juice
  • 1 tablespoon (15 ml), or a peasize sample, of each solid food sample: banana, sugar, onion, pasta
  • 8 baby-food jars
  • distilled water
  • monosaccharide testing solution (see Appendix 5)
  • forceps or pot holder

Procedure

  1. Prepare a water bath by filling the pot with 2 inches (5 cm) of water.
  2. Place the pot of water on the stove and heat to boiling.
  3. While the water is heating, prepare the food samples by placing each sample in a separate baby-food jar (see Figure 10.1).
  4. Carbohydrates: Mono-, Di-, and Polysaccharides

  5. Add 1 tablespoon (15 rol) of distilled water to each jar containing a solid food sample.
  6. Prepare a data table such as the one shown here. Note: Ust all eight food samples.
  7. Test for the presence of monosaccharides in each food sample by:
    • adding 1 tablespoon (15 ml) of testing solution to the jar.
    • observing and recording the color of the solution in the jar.
    • setting the jar in a pot of boiling water and heating for three minutes.
    • using forceps or a pot holder to carefully remove the hot jar.
    • observe and record the color of the solution in the jar again.
  8. Determine the concentration of the monosaccharide present in each food sample by comparing the final color of the solution with the following color chart:
      blue—zero
      green—low concentration
      light to dark yellow—moderate concentration
      orange to red—high concentration

Results

The author's results indicated that the soda, honey, apple juice, and onion had the highest amount of simple sugars; the banana, a moderate amount; and the pasta, diet soda and table sugar (sucrose). no monosaccharides. Note: The results will vary depending on the brand of food tested and on the conditions and length of time the food has been stored.

Why?

The monosaccharide testing reagent contains copper II ions (Cu++). Solutions containing copper II ions are blue. Sugars such as glucose and fructose provide electrons needed to change the copper II ions to copper I ions (Cu+) and elemental copper (CU0). These simple sugars function as reducing agents because they provide electrons during a chemical reaction. The color of the copper testing solution changes from blue to red as the copper II ions are first changed into copper I and then elemental copper. With disaccharides or polysaccharides. the testing solution remains blue.

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