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How Sweet It Is! Measuring Glucose in Your Food

Difficulty
Time Required Average (6-10 days)
Prerequisites None
Material Availability Readily available.
Cost Low ($20 - $50)
Safety No issues

Abstract

You know that sugar makes food sweet. But did you know that there are different kinds of sugar? Sucrose is the granulated sugar that you usually use for baking. Another kind of sugar, which is found in honey and in many fruits, is glucose. In this science fair project, you will measure the concentration of glucose in a variety of foods. You will use special strips that change color in response to glucose, to measure the glucose concentration in different foods.

Objective

To measure the concentration of glucose in a variety of common fruits and juices.

Credits

David Whyte, PhD, Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "How Sweet It Is! Measuring Glucose in Your Food" Science Buddies. Science Buddies, 6 Oct. 2014. Web. 26 Oct. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p049.shtml?from=Blog>

APA Style

Science Buddies Staff. (2014, October 6). How Sweet It Is! Measuring Glucose in Your Food. Retrieved October 26, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p049.shtml?from=Blog

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Last edit date: 2014-10-06

Introduction

Fresh pineapple, chilled watermelon, and an icy cold soft drink on a hot summer's day. What do these things have in common? They all taste so good because of the sweetness the sugar in them provides. When you think of sugar, you probably picture the white granules you put in cookies, that your parents put in their coffee, or that you put on your cereal. Actually, this is just one kind of sugar, called sucrose, which is extracted from sugar cane or sugar beets. Technically, sugar is a carbohydrate that occurs naturally in every fruit and vegetable. It is the major product of photosynthesis, the process by which plants transform the Sun's energy into food.

Glucose is another type of sugar and is a very important biochemical. For one thing, glucose is the only fuel used by brain cells. Glucose is also an important source of energy for muscles and other tissues in the body.

The glucose in your blood comes from the food you eat. Complex carbohydrates, found in pasta or cereal, for example, are long chains of sugar molecules that are broken down by enzymes to simple sugars, such as glucose. Sucrose, or table sugar, is also broken down to form glucose. Because carbohydrates and sucrose in food are broken down to form glucose, the level of glucose in your blood goes up after you eat.

Like most of the chemicals in your blood, the level of glucose must be tightly controlled. The level of glucose in your blood is controlled by insulin, a hormone made in the pancreas. Too little glucose, and your brain and other organs will not have the energy they need to function. Too much glucose in the blood can cause diabetes, which is a serious and growing health problem in the United States.

In this science fair project, you will investigate the concentration of glucose in common fruits and juices. In order to measure the glucose concentration, you will use glucose strips. These strips were developed to help people with diabetes maintain a healthy level of blood glucose. When you dip the test strip into a liquid, such as orange juice, it changes color if glucose is present. The degree of color change depends on the concentration of glucose.

Terms and Concepts

  • Sucrose
  • Carbohydrate
  • Glucose
  • Biochemical
  • Complex carbohydrate
  • Enzyme
  • Insulin
  • Hormone
  • Pancreas
  • Control
  • Negative control
  • Positive control
  • Dilution series

Questions

  • Put these five food sugars in order, from the sweetest to the least sweet: glucose, fructose, sucrose, lactose, and maltose.
  • What is the concentration range of glucose in healthy people? What is the level in diabetics?
  • Which foods have a naturally high level of glucose?
  • Which fast foods have the highest glucose levels? (Hint: Look at the nutrition data on the restaurants' websites.)
  • Why do certain foods have high natural sugars? (Hint: Fruits contain seeds, and the plant's chances of spreading are better if the seeds are dispersed).
  • How many calories are in 1 gram (g) of glucose?
  • How does the glucose test strip work?

Bibliography

Materials and Equipment

  • Disposable cups, at least 8 oz. (8 plus one for each food or juice you want to test)
  • Permanent marker
  • Glucose tablets with 4 g of glucose per tablet; available at most drug stores or online at Amazon.com.
  • Optional: Knife and spoon
  • Water
  • Graduated cylinder (100 mL volume); available online at Amazon.com.
  • Diastix® glucose test strips for urinalysis (8 plus three for each food or juice you want to test); available at drug stores or online at Amazon.com.
  • Foods and juices to test. Categorize as fresh or processed. Some examples are listed below.
    • Fruit juices: orange juice, lemon juice (you will be surprised!)
    • Fresh fruit (sliced): apple, pear, pineapple, cucumber, tomato
    • Processed foods: soft drinks, diet soft drinks, salad dressing, baby food, vinegar, peanut butter, sauces used on fast food hamburgers, ice cream (melted)
    • Miscellaneous: honey, sugar water (sucrose mixed with tap water), molasses
  • Graduated cylinder (10 mL volume), available at Amazon.com, or measuring teaspoons
  • Stopwatch or clock with a second hand
  • Adult helper
  • Lab notebook

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Experimental Procedure

  1. To start this science fair project, you should first collect all of the foods and juices that you plan to test.
  2. Based on your research, predict which foods will have the highest glucose levels. List the foods in your lab notebook in order from highest to lowest predicted glucose concentration.
    1. For processed food, the labels on most products list total sugar, which is a mixture of sucrose, fructose, and glucose. The test strip only measures glucose concentration. The actual level of glucose is usually available online, at the company's website, or at sites such as www.nutritiondata.com.

Making the Positive and Negative Controls

Controls are samples with known ingredients that should give clear, expected results. They are used to test the procedure. Using a positive control, there should be a clear "signal," or color change, showing that the glucose strips are working properly. Using a negative control, there should be no "signal," or color change. Tap water is a suitable negative control (because it has no glucose).

  1. First, make the positive controls using water and the glucose tablets. To do this, make a dilution series using sequential twofold dilutions to create the following concentrations: 4%, 2%, 1%, 0.5%, 0.25%, 0.125%, and 0.0625%.
    1. Label seven cups 1–7.
    2. Add 8 grams (g) of glucose to 200 milliliters (mL) water in cup #1 to make the 4% solution and stir until the glucose dissolves.
      1. Tip: The glucose tablets will dissolve faster if they are first cut into small pieces and then crushed (such as by using the back of a spoon).
    3. Add 100 mL of water to each of the six remaining cups (2–7).
    4. Add 100 mL of the 4% solution to cup #2 to make a 2% solution. Stir well.
    5. Then add 100 mL of the 2% solution to cup #3 to make a 1% solution. Stir well.
    6. Repeat for the remaining dilutions. Make sure to rinse the container you are using to transfer the 100 mL volumes between each dilution and use a clean stirrer.
      1. When you are done, each cup should have 100 mL of liquid, except for the 0.0625% solution, which should have 200 mL.
  2. Label an eighth cup #8 and add 100 mL water to it. Do not add any of the glucose solutions to it. This will be a 0% solution and will be your negative control.
  3. If you used glucose tablets that are dyed red, you should now have eight cups that look like the ones in Figure 1 below.
Dilution series of glucose in water.
Human Biology science project

Figure 1. If you used glucose tables that are dyed red, the glucose dilution series should look like the ones in this picture (arranged by most concentrated to least, from left to right). (Each cup should have 100 mL of liquid, except for the 0.0625% solution, which should have 200 mL.) An eighth cup, serving as the negative control, should only contain water (on the far right in this picture).

  1. Dip a test strip into each of the eight cups, one at a time. Watch the test strip for 30 seconds (which should be the time recommended in the test strip instructions) and match the color of the test strip to the color on the bottle. Do the colors match what you would expect? Write down your observations in your lab notebook.
    1. Note: The colors on the bottle will not exactly correspond to the percent glucose solutions you made. On the bottle there will probably be colors for 0% ("Negative"), 0.1% ("1/10"), 0.25% ("1/4"), 0.5% ("1/2"), 1% ("1"), and 2% ("2") glucose solutions, as shown in Figure 2 below.
    2. Some test strip colors may fall between two of the colors on the bottle, for example between "1/2" and "1." If this happens, write down the two numbers in your lab notebook and calculate their average.
    3. If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%").
    4. If you do not have a clear color change for any of the positive control solutions with a concentration greater than 0.0625%, or if the test for any solution is more than one color off from what it is expected to be (for example, if the 1% solution reads less than 0.5% or the 0.25% solution reads greater than 0.5%), repeat the procedure; if it still is problematic, buy new test strips.
    color chart on a glucose test strip bottle
Human Biology science project

    Figure 2. This is the color chart on a glucose test strip bottle. After a glucose test strip is dipped in a glucose solution, its color should match a color on its bottle (or be between two colors). The color on the bottle will indicate the percentage of glucose in the solution tested.

Testing the Foods for Glucose Concentration

  1. Pour a small amount of liquid that you plan to test into a cup.
  2. Get ready to start the stopwatch.
  3. Dip the test strip into the liquid.
    1. For the fresh fruits and vegetables, press the test strip against a freshly cut slice until the test strip is thoroughly wet.
    2. For very high-glucose liquids, such as honey or soft drinks (not diet), or viscous substances, such as peanut butter, molasses, or baby food, dilute the samples in water prior to testing. For example, mix 2.5 mL (0.5 teaspoon [tsp]) of honey with 22.5 mL (4.5 tsp.) water makes a 1-to-10 dilution. Multiply the concentration of glucose in the diluted solution by 10 to obtain the concentration of glucose in the original sample.
  4. Start the stopwatch as soon as the test strip has been dipped.
  5. Wait for the amount of time specified on the test strip directions, usually 30 seconds.
  6. Compare the color on the test strip with the color on the side of the container to determine the glucose concentration.
    1. If the color changes to the maximum range (2 percent) before 30 seconds, list it as greater than 2 percent, "> 2%."
    2. To determine the actual percent of glucose in samples with over 2 percent, dilute the sample as described in step 3b to bring the glucose level down within the range of the test strips.
    3. Test the diluted sample. If it has 1 percent glucose, then the glucose in the sample is really 10 percent, because you diluted it 10-fold.
  7. Repeat steps 1–6, of this section, for all of your foods and juices.
  8. Make a data table of your results in your lab notebook. Table 1 below is an example, with a "predicted" column for what you expected to find, and an "experimental" column for your actual results.
  9. Use < for="" "medium,"="" and="" "low,"="" 1%–2%="" 5%="">2% for "high."
  10. Repeat the glucose measurements for a total of at least three trials (three samples of each type of food).
  11. Graph your results. Put the type of food on the x-axis and the glucose concentration on the y-axis.
  12. Did your results match your predictions? Were some foods surprising in the amount of glucose they contained?
Type of Food Glucose Level: Predicted Glucose Level: Experimental Notes
Mixed fruit drink High 10% (1% in diluted sample) Diluted 1:10 (example)
Orange juice Low 1% Tropicana
    
Table 1. In your lab notebook, make a data table like this one to record your results in.

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Variations

  • People with diabetes might occasionally experience low blood sugar. When this occurs, they need to eat or drink something with glucose in it right away, typically aiming for a fast intake of 15 g. Calculate how much of each food you tested would need to be consumed to provide 15 g of glucose.
  • Do different honeys have different glucose levels? You can investigate this by repeating this experiment and focusing on comparing different honeys.
  • Test the glucose levels in fresh vs. frozen foods. Is there a difference in the amount of glucose a food has depending on whether it is fresh or frozen?
  • For a more advanced project on glucose in foods, see: Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food.

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