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Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food

Difficulty
Time Required Average (6-10 days)
Prerequisites None
Material Availability The invertase for this science project needs to be specially ordered. See the Materials and Equipment section for more details.
Cost Low ($20 - $50)
Safety No issues

Abstract

Maple syrup on pancakes, ripe bananas, and soft drinks are all foods that are tasty to us because of the sugar in them. But did you know there are different kinds of sugar? One food can have multiple kinds of sugar in it, and our bodies actually process the different types of sugars differently. In this science project, you will measure the concentration of two sugars, glucose and sucrose, in different foods and investigate how sucrose is converted into glucose with the help of an enzyme called invertase.

Objective

To investigate how an enzyme converts sucrose into glucose and how this changes the amount of glucose we digest from different foods.

Credits

Teisha Rowland, PhD, Science Buddies

Andrew J. Bonham, PhD, Metropolitan State University of Denver

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Last edit date: 2013-11-16

Introduction

We are often confronted by tasty sweet foods. The appealing sweetness of these foods is due, of course, to the sugar in them. And if you read the nutrition labels on sweet foods, you will find that they are often bursting with sugar: a 12 ounce (oz.) soft drink can have about 40 grams (g) of sugar, an 8 oz. glass of orange juice can have around 25 g of sugar, and just ¼ cup of pure maple syrup (a suggested serving size) can have 50 g of sugar! (For reference, a new penny weighs 2.5 g.) There are actually several different kinds of sugars, which are all technically carbohydrates (chemical compounds that only have carbon, hydrogen, and oxygen, and are mostly made by plants).

The sugar you probably see most often is sucrose, the white granules of sugar used for baking cookies or making lemonade. Sucrose is extracted from sugar cane or sugar beets. Glucose is another kind of sugar commonly found in foods. In the body, sucrose is actually broken down to create glucose and another kind of sugar, fructose. Glucose and fructose are the most basic type of carbohydrates (called monosaccharides) and, during digestion, are absorbed directly in the intestines. The process of breaking down sucrose into glucose is catalyzed, or made faster, by an enzyme. Enzymes are proteins that help make many different chemical reactions faster. In the human body, the enzyme that catalyzes this reaction is called sucrase. Researchers who want to study this reaction often use similar proteins and enzymes made by other organisms because it can be expensive to use human proteins and enzymes. For example, in plants and yeast, an enzyme called invertase catalyzes the same reaction as sucrase does in humans. This reaction is shown in Figure 1 below.

The reaction between sucrose and invertase that produces glucose and fructose.
Human Biology science project
Figure 1. Sucrose can be converted to glucose and fructose by the enzyme invertase.

Glucose is a simple sugar that is important biologically because it is the primary fuel, or energy source, used by cells, such as brain cells, muscle cells, and cells in other tissues of the body. In addition to being made by the breakdown of sucrose, glucose is also made in the body by the breakdown of other carbohydrates, such as starch (foods rich in starch include bread, cereals, pasta, etc.). Because sucrose and carbohydrates in food are broken down to form glucose, the level of glucose in a person's blood (commonly referred to as the blood glucose level) usually goes up after he or she eats.

Like most of the chemicals in your blood, glucose must be tightly controlled. The level of glucose in your blood is regulated by insulin, a hormone made by the pancreas. When blood glucose levels rise after eating a meal, the pancreas releases insulin, which causes cells in the body (such as liver, muscle, and fat cells) to take up glucose, removing it from the bloodstream and storing it to use for energy. When the blood glucose levels start falling, the pancreas stops releasing insulin, and the stored glucose is used for energy.

Dangerous medical conditions can develop if there is either too little or too much glucose in a person's bloodstream. If there is too little, the brain and other organs will not have the energy they need to function, a condition called hypoglycemia. This can be a serious, life-threatening condition; to treat it, a person with hypoglycemia must raise his or her blood glucose levels, usually by eating large amounts of foods rich in glucose or carbohydrates.

If there is too much glucose in the blood (hyperglycemia), it can be a sign of diabetes, which is a serious and incurable—and growing—health problem. If a person's pancreas does not make enough insulin, or his or her body does not respond to insulin (called insulin resistance), this can result in high blood glucose levels and diabetes. This is why a person with diabetes may need daily insulin injections. However, a complication of treating diabetes is that it can actually cause hypoglycemia in certain circumstances. Watch this video to see how glucose is normally taken up from the bloodstream by cells, and how problems with this process define the two types of diabetes: Type I and Type II.

Video ProjectIdea Glucose Khana Academy
This video shows how glucose is normally taken up from the bloodstream by cells, and how problems with this process can cause diabetes.
Watch this Khana Academy video https://www.khanacademy.org/science/healthcare-and-medicine/endocrinology-and-diabetes/v/glucose-insulin-and-diabetes that shows shows how glucose is normally taken up from the bloodstream by cells, and how problems with this process can cause diabetes.

In this science fair project, you will investigate the concentration of glucose and sucrose in different common foods, and how the conversion of sucrose to glucose (using the enzyme invertase) changes how much glucose we actually digest from different foods. If someone has hypoglycemia and needs a fast glucose boost, which foods are good to eat? Which foods should be avoided? While sucrose is converted to glucose, this takes some time to happen. If someone has diabetes, which foods are good to eat in moderation not only because they are high in glucose, but also because they are high in sucrose? Which foods may be safe for someone with diabetes to consume because they do not change blood glucose levels much?

To measure glucose concentrations, you will use glucose test strips. These strips were developed to help people with diabetes monitor their level of blood glucose (by measuring the amount of glucose in their urine). 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. After you treat each food item with invertase, you will also be able to use the glucose test strips and some knowledge of enzyme kinetics, which will be discussed later, to calculate how much sucrose is in each food and how much glucose may end up in our bodies.

Terms and Concepts

  • Sugar
  • Carbohydrates
  • Sucrose
  • Glucose
  • Monosaccharides
  • Catalyst
  • Enzymes
  • Sucrase
  • Invertase
  • Cellular energy
  • Blood glucose levels
  • Insulin
  • Hypoglycemia
  • Hyperglycemia
  • Diabetes
  • Insulin resistance
  • Enzyme kinetics
  • Controls
  • Positive control
  • Negative control
  • Dilution series
  • Product inhibition
  • Linear relationship

Questions

  • Which typical foods have a high level of glucose, sucrose, or both?
  • Which typical foods are low in glucose, sucrose, or both?
  • What is the concentration range of glucose in healthy people? What is the range used to diagnose someone with diabetes?
  • Besides invertase, what other enzymes convert carbohydrates into glucose?
  • The enzyme in humans that converts sucrose to glucose and fructose is actually called sucrase, but invertase is used because it is much cheaper and easier to purchase. How is sucrase different than invertase? What organisms make invertase?
  • Why is invertase used in baking?

Bibliography

These resources are a good place to start gathering information about glucose, sucrose, and diabetes:

Materials and Equipment

  • Disposable cups, at least 8 oz. (at least 25)
  • 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 milliliter [mL] volume); available online at amazon.com.
  • Diastix® glucose test strips for urinalysis (at least 60); available at drug stores or online at amazon.com.
  • Kitchen measuring spoons, half-teaspoon and tablespoon
  • Timer or clock with a second hand
  • Sucrose, also known as table sugar or granulated sugar, commonly used in baking (6 g)
  • Scale, must be able to accurately measure 6 g. A digital scale accurate to at least 1 g (the Fast Weigh MS-500-BLK Digital Pocket Scale) is available from amazon.com.
  • LorAnn Oils Invertase (1 oz.); available at some gourmet stores (it is used in baking) or online at LorAnn Oils or amazon.com. Be sure to keep it refrigerated.
  • Bottle caps (at least 5)
  • Foods to test (must be in liquid or mushy form). Try at least five different foods. Here are some examples:
    • Drinks: Milk, silk soy milk, soft drinks (diet and/or regular), fruit juice (such as orange juice)
    • Baby food: Meat, starchy vegetables, squash, bananas, pineapple, oranges, carrots, yams, cherries, beans
    • Miscellaneous: Maple syrup, honey, ice cream (melted), molasses, peanut butter, salad dressing
  • Medicine dropper
  • Lab notebook

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Experimental Procedure

Testing the Glucose Strips

In this part of the science project, you will create controls, or samples with known ingredients that should give clear, expected results. You will do this to make sure that the glucose test strips are working properly. If the strips are not working properly, then the rest of this experiment will not work. The positive controls will contain different concentrations of glucose. The negative control will be a sample without 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: 4%, 2%, 1%, 0.5%, 0.25%, 0.125%, and 0.0625%.
    2. Add 8 grams (g) of glucose to 200 mL of water in the cup labeled 4% 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 (for instance, by using the back of a spoon).
    3. Add 100 mL of water to the other six cups.
    4. Measure 100 mL of the 4% solution and add it to the cup labeled 2% to make a 2% solution. Stir well.
    5. Measure 100 mL of the 2% solution and add it to the cup labeled 1% to make a 1% solution. Stir well.
      1. Between each dilution, make sure to rinse and shake the excess water from the graduated cylinder or container you are using to transfer the 100 mL volumes. Also, use a clean stirrer.
    6. Repeat this process for the remaining dilutions.
      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. Fill an extra cup with 100 mL water. Do not add any of the glucose solutions to it. Label it 0%. This 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 2 below.
Dilution series of glucose in water.
Human Biology science project
Figure 2. 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. See the Technical Note below for guidance on matching the color of the glucose test strips to the color on the bottle.
    2. If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%"). You do not need to perform a dilution.
    3. 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 and repeat the procedure.
    4. Tip: If you would like additional help with reading the glucose test strips, check out the Frequently Asked Questions (FAQ) for this science project.
Technical Note

When matching the color of a glucose test strip to a color on the bottle, keep in mind these helpful tips:

  • The colors on the bottle will not exactly correspond to the percent glucose solutions you made. 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 3 below.
  • 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.
  • If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%"). Depending on where this happens in the Experimental Procedure, you may need to then perform a 1:10 dilution and re-test the sample. There are two ways in which you may perform a 1:10 dilution, and the preferred way will be specified in the text:
    • On a bottle cap, add 9 drops of water and 1 drop of the test solution.
    • Mix 1/2 teaspoon (tsp.) (2.5 mL) of the sample with 22.5 mL water to make a 1:10 dilution. (Note: You will only test 15 mL of this dilution.)

Remember that if the 1:10 dilution reading reports 1% glucose, then the glucose in the sample is really 10%, because it was diluted tenfold.

color chart on a glucose test strip bottle
Human Biology science project
Figure 3. 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 Invertase Activity

In this next part of the science project, you will test the activity of the invertase enzyme. It is important for you to do this step so that you know how long you should test your selected foods with the invertase enzyme. You will test the activity of the invertase enzyme by investigating how long it takes it to turn a known amount of sucrose (in solution) into glucose. You can look at Figure 1 above to see the chemical reaction. When invertase is added to the sucrose solution, the concentration of glucose should increase over time as the sucrose is converted to glucose. However, after some amount of time, the concentration of glucose will appear to remain the same, or plateau. For an example, see Figure 4 below. Although the invertase may still be converting sucrose to glucose, it is doing it at an extremely reduced rate. This is probably partly due to product inhibition, which is when the product of a reaction (glucose in this case) stops the enzyme (invertase) from making more product. Here you will determine how much time is needed for the invertase enzyme to convert some, but not all, of the sucrose in a 10% solution, before product inhibition occurs and the reaction clearly slows down. This part of the project is an example of the study of enzyme kinetics.

  1. Make a solution containing 10% sucrose.
    1. Fill a cup with 60 mL of water.
    2. Add 6 g of sucrose to the cup of water. Mix until all the sucrose dissolves.
    3. Put 15 mL (1 Tbsp) of this solution into a new cup.
      1. How many grams of sucrose are in 15 mL of the 10% solution?
  2. In your lab notebook, make a table for recording your data. You will be taking glucose readings over time to see how much sucrose has been converted to glucose by the invertase enzyme.
    1. Starting at zero, plan on taking glucose readings every five minutes for the first 30 minutes, and then every 10 minutes after that. Plan on taking readings for 90 minutes total.
  3. Use a glucose test strip to determine the concentration of glucose in the sucrose solution, as you did in the "Testing the Glucose Strips" section above in step 4. Write your result in the table in your lab notebook under "0 minutes."
    1. There should be 0% glucose in the sucrose solution.
  4. Set a timer for 90 minutes or make sure a clock is nearby.
  5. Right before using it, remove the invertase from the refrigerator.
    1. Do not let the invertase stay outside of the refrigerator long. Enzymes can degrade over time, but keeping them cool helps to prevent them from degrading. Make sure to return the invertase to the refrigerator quickly after adding it to the sucrose solution.
  6. Add 10 drops (about 0.5 mL) of invertase to the sucrose solution. Quickly mix the solution.
  7. Start the timer or write down the exact time in your lab notebook.
  8. Use the glucose test strips to take glucose readings of the solution over time, as described in step 2 above.
    1. Write your results in the table in your lab notebook.
    2. See the Technical Note above for guidance on matching the color of the glucose test strips to the color on the test strip bottle.
    3. If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%") and quickly perform a 1:10 dilution using 1 drop of your test solution (as described in the Technical Note above on the third bullet point) to determine the actual percentage of glucose in the sample. Take a glucose reading of the 1:10 dilution.
    4. When the glucose reading has remained the same for at least 20 minutes (3 readings spaced 10 minutes apart), you can stop taking readings.
  9. Graph your results. Put the time on the x-axis and the glucose concentration on the y-axis.
    1. You should end up with a graph that roughly looks similar to Figure 4 below.
Graph of invertase reacting with sucrose to creating an increased concentration of glucose over time.
Human Biology science project
Figure 4. Initially, the invertase enzyme converts sucrose to glucose at a roughly constant rate, creating a linear, or nearly straight, line. However, after some amount of time, the concentration of glucose appears to remain roughly the same, or plateau. Although the invertase may still be converting sucrose to glucose, it is doing it at an extremely reduced rate. The red asterisk marks where the glucose concentration first leveled off. The green asterisk, which we will call the linear time point, marks the time point at which the glucose concentration was half what it was at the red asterisk. Your actual data may only roughly match the line in this graph.
  1. Analyze your results.
    1. When the glucose concentration first leveled off, what was the glucose reading?
      1. For example, in Figure 4 above, this point is marked with a red asterisk.
    2. Divide this concentration in half. At about what time was this glucose reading taken? Write this time in your lab notebook as the "linear time point."
      1. For example, in Figure 5 above, this point is marked with a green asterisk.
  2. The "linear time point" you determined in step 10b is the time you will use to test your selected foods.
    1. This is because this time point is when the invertase enzyme is clearly making the reaction occur at a roughly constant rate (it is a point on a linear, or nearly straight, line). Also, it is well before the reaction starts slowing down, which can cause inaccuracies in measuring the glucose concentration.

Testing the Foods for Glucose Concentration Before and After Adding Invertase

Now that you have determined your linear time point, you are ready to test your selected foods. In this part of the science project, you will first test the glucose concentration of your selected foods and then react each with invertase to determine how this changes their glucose concentrations.

  1. In your lab notebook, make a table for recording your data.
    1. For each food sample, you will take two glucose readings: one before adding the invertase and one after, at the linear time point you determined in the "Testing Invertase Activity" section above in step 10b.
    2. Test at least three different samples of each selected food.
      1. Multiple trials help scientists make sure that their results are accurate and reproducible.
  2. Label the cups with the food samples you will test.
  3. Let all of the food samples you will test come to room temperature before testing them.
    1. The activity of an enzyme is affected by temperature. It is important that all of the test foods are about the same temperature, so that any differences you see in your data are not because the foods were of differing temperatures.
  4. For foods with high amounts of sugar, such as soda (not diet), or viscous substances, such as syrup, molasses, baby food, or peanut butter, dilute the samples 1:10 in water before testing them. Make the 1:10 dilution using 1/2 tsp. of your sample (as described in the Technical Note above, in the third bullet point).
  5. To each cup, add 1 Tbsp. (15 mL) of the food that you will test.
  6. Use a glucose test strip to determine the concentration of glucose in each food sample, as you did in the "Testing the Glucose Strips" section above in step 4.
    1. See the Technical Note above for guidance on matching the color of the glucose test strips to the color on the bottle.
    2. If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%") and perform a 1:10 dilution using 1/2 tsp. of your sample (as described in the Technical Note above, in the third bullet point). Use the diluted sample for all tests.
  7. Write the glucose concentration for each sample in your table.
  8. Set a timer for the linear time point you determined or make sure a clock is nearby.
  9. Add 10 drops (about 0.5 mL) of invertase to each food sample. Quickly mix the samples.
    1. Start only a few samples at a time so it is easier to manage them.
    2. Other than taking it out to quickly add to the samples, the invertase solution should remain in the refrigerator.
  10. Start the timer or write down the exact time in your lab notebook.
  11. At the linear time point, use a glucose test strip to determine the concentration of glucose in each sample. Write this in your table.
    1. See the Technical Note above for guidance on matching the color of the glucose test strips to the color on the bottle.
    2. If the color changes to the maximum range (2%) before 30 seconds, list it as greater than 2% (">2%") and perform a 1:10 dilution using 1 drop of your test solution (as described in the Technical Note above, in the third bullet point). Take a glucose reading of the 1:10 dilution.
  12. Graph your results. Make a bar graph and put the food names of the samples on the x-axis and the glucose concentration on the y-axis. Include both glucose readings for each sample (before adding invertase and at the linear time point).

Analyzing Your Results

  1. Look at the graph you made in the "Testing the Foods for Glucose Concentration Before and After Adding Invertase" section (step 12). Do the glucose readings you took before adding the invertase match what you would expect for these foods?
    1. Which foods had the most glucose before adding the invertase? Which had the least? Did any have no glucose?
  2. Using the data you collected, you can determine the sucrose concentration in each of the foods you tested.
    1. Look at the graph you made in the "Testing Invertase Activity" section. At the linear time point, what was the glucose concentration? If you multiply the glucose concentration at the linear time point by the original sucrose concentration (10%), this will tell you what percentage of the total sucrose was converted to glucose at this time point. We will call this value "Percentage of sucrose converted." You can see this equation written out in Equation 1 below.
      1. For example, if at the linear time point the 10% sucrose solution had a reading of 2% glucose, then this means that 20% of the total sucrose (10% multiplied by 2%) had been converted to glucose.

        Equation 1.
        Original sucrose concentration × Glucose concentration at linear time point = Percentage of sucrose converted
    2. Look at the data you collected in the "Testing the Foods for Glucose Concentration Before and After Adding Invertase" section. To determine the original sucrose concentration of each of your food samples, use Equation 1 and divide the percentage of sucrose converted (which you just determined) by the glucose concentration at the linear time point.
      1. For example, if at the linear time point a food had a 2.5% glucose reading, and we calculated that the percentage of sucrose converted is 20%, then we could calculate that the original sucrose concentration of this food was 8% (20% divided by 2.5%).
    3. Which food(s) had the highest original sucrose concentration? Which food(s) had the lowest? Did any foods have no sucrose? Do your results match your predictions?
  3. How did the sucrose concentration in the different foods affect the glucose concentration at the linear time point?
  4. How might this experiment be different from what takes place in the human digestive system? Do you think that even more glucose might have been made at the linear time point due to other chemical reactions taking place?
    1. Hint: Re-read the Introduction.
  5. How do your results compare to the amount of sugar listed for these foods on their packaging?
    1. You can also take a look at the "Ingredients" to see what types of sugars might be in the foods. High-fructose corn syrup actually contains fructose and glucose.
  6. Knowing the sugar contents of different foods is particularly important for someone with diabetes. If someone has hypoglycemia and needs a fast glucose boost, which foods would you recommend eating? Which foods would you recommend avoiding? Which foods would you recommend eating in moderation not only because they are high in glucose, but also because they are high in sucrose? Which foods may be safe for someone with diabetes to consume because they do not change blood glucose levels that much?

Troubleshooting

For troubleshooting tips, please read our FAQ: Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food.

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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. How much of the different food samples you tested would need to be consumed to provide 4 g of glucose quickly? How much longer would it take for a food with relatively more sucrose to be converted into 4 g of glucose? Tip: You can find out more about blood sugar levels after eating a meal by watching this video: Khan Academy. (n.d.). Blood sugar levels. Retrieved March 16, 2012, from http://www.khanacademy.org/science/healthcare-and-medicine/v/blood-sugar-levels
  • You can build a typical "meal" out of different baby foods and test it with this experiment. How much glucose and sucrose is in a typical meal? What parts of the meal add the most glucose? What foods would be good to substitute for foods with high amounts of glucose?
  • Enzyme activity can be significantly affected by pH. Pick a food you tested that had a lot of sucrose, or just use a sucrose solution, and add acid or base to make it more acid or more basic. Check the pH of the solutions using pH test strips and then test the invertase activity in each. At which pH did the enzyme work best? At which pH was it worst? How might this have affected your results in this project? For more information on acids, bases, and pH, see: Acids, Bases, & the pH Scale.
  • In this project you tried to mimic one type of chemical reaction that occurs in the human digestive system, but it can be very difficult to mimic an entire biological system. How could you make this project more similar to what happens in the human digestive system? What other reactions might be making glucose that you could also mimic?
  • For a less advanced project on glucose in foods, see: How Sweet It Is! Measuring Glucose in Your Food.

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Frequently Asked Questions (FAQ)

If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: I am getting unexpected results. The ingredients I am testing seem to have more or less glucose than I expect them to have. Why might this be?
A: There could be several reasons for this:
  • If you let the invertase enzyme sit out at room temperature long, this can quickly decrease its activity. Enzymes naturally degrade over time, but keeping them cool helps to prevent them from degrading. Always keep the invertase enzyme in the refrigerator when you are not using it, such as immediately after adding the drops to a test item.
  • If your readings are maxing out on the glucose test strips (they read 2% glucose), your results may be skewed such that it looks like your ingredients have less glucose than they actually do. If the color changes to the maximum range (2%) before 30 seconds, make sure to perform a dilution, as described in the Technical Note at the top of the Procedure, and re-test the diluted version of the ingredient.
  • The ingredients you tested (or the 10% sucrose solution you made) were not at room temperature. The activity of enzymes is affected by temperature, so if the temperature of your sugar solution and ingredients was not consistent (or, similarly, the water you used in your dilutions was not at room temperature), the invertase will behave differently so your results may be inconsistent or unexpected.
  • 15 mL of each sample was not tested. Since you initially test the enzyme activity with 15 mL of the 10% sugar solution, make sure to test the same amount (15 mL) of each ingredient. If you have to dilute an ingredient, be sure to use 15 mL of the diluted sample when testing it with the enzymes.
Q: I am having trouble reading the glucose test strips. What should I do?
A: Look at the Technical Note in the Procedure and the accompanying Figure 3 to see if that helps you figure out how to read your glucose test strips. Here are some tips:
  • Match the test strip to the color chart on the bottle when it has been exactly 30 seconds since you dipped the test strip in the sample. (You may see the test strip continually change colors, so it is important to check it at this exact end time so you are matching the right color.) It may help to hold the test strip next to the chart for the entire 30 seconds and during that time, try to match the test strip color to the color chart so that when it has been 30 seconds you will already have a good idea of which color on the chart your strip matches.
  • It is OK and common for a color on a test strip to not exactly match a color shown on the color chart on the glucose test strip bottle. If this happens, do your best to figure out which color on the chart it is closest to, or where it falls between two different colors on the chart.
  • If the color changes to the maximum range (2%) before 30 seconds, you will need to make and test a dilution of your sample if you are testing your ingredient samples. See the Technical Note in the Procedure for how to do this. If you do not do this, your results may be lower than expected.
Q: The glucose in my samples decreased after I added the invertase enzyme. What should I do?
A: The enzymes should not cause a decrease in the amount of glucose in the samples. The amount of glucose should either stay the same or increase. It is possible that the glucose test strips were read incorrectly or did not function properly. We recommend you re-test a new sample of your ingredient if you see this happen. You may also want to test dilutions of your sample if it looks like it might be maxing out the glucose test strips (in other words, the glucose readings are at 2% or above).
Q: I graphed the invertase activity on the 10% sucrose solution and it looks like there is less than 10% glucose in the solution when the enzyme activity plateaus. Should I be concerned?
A: It is normal to have less than 10% glucose in the solution after using the invertase on the 10% sucrose solution. This is because the invertase may not convert all of the sucrose to glucose due to product inhibition, the enzymes' activity leveling off, and the time restraints of the experiment. You should not be concerned if you see this. Because you are using the linear time point in your experiments, you should be able to determine the original sucrose concentrations of your food items by following the steps in the "Analyzing Your Results" section of the Procedure.
Q: I want to save a copy of my glucose test strips to put on my project display board. How can I do this?
A: You probably noticed that the glucose test strips change color over time (which is why it is important to read them at exactly 30 seconds after dipping them in the sample). Consequently, it is difficult to save them in a way that also shows your results. What you could do is try to take a picture of your glucose test strips (in full lighting), but it may be tricky because you will want to capture them at exactly 30 seconds. You should also consider taking a picture of the color chart on the bottle for reference.

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