Lactose, Sucrose, and Glucose: How Many Sugars are in Your Smoothie?
AbstractDo you enjoy drinking smoothies packed full of berries and other tasty fruits? Or maybe you like drinking a creamy milkshake with peanut butter, chocolate, and bananas. Smoothies and milkshakes are often tasty to us because of the sugar in them. But did you know there are different kinds of sugar? Some ingredients in a smoothie can have more than one kind of sugar in them, and our bodies process each kind of sugar differently. In this science project, you will measure the concentration of three sugars (glucose, sucrose, and lactose) in common smoothie and milkshake ingredients by investigating how sucrose and lactose are converted into glucose with the help of digestive enzymes in your body.
Teisha Rowland, PhD, Science Buddies
Thanks to Andrew Bonham, PhD, Metropolitan State University of Denver, for feedback with testing this science project.
Recommended Project Supplies
Investigate how digestive enzymes convert sucrose and lactose into glucose, and use this information to evaluate the glucose content of your own smoothie recipes.
Do you like smoothies packed full of fruit, or tasty chocolate milkshakes? Smoothies and milkshakes are often appealing because of their sweetness, which is due, of course, to the sugar in them. If you ever look up the nutritional information on some of the ingredients that go into a homemade smoothie or milkshake, you may be surprised to find that some of them have a lot of sugar: a tablespoon of honey can have 17 grams (g) of sugar and a whole banana has around 15 g of sugar! But other ingredients have a lot less sugar; for instance, a tablespoon of ice cream often has less than 2 g of sugar, and the same amount of whole milk has nearly 0 g of sugar. 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).
Figure 1. Your taste buds care about which ingredients go in to your smoothie, but your body cares more about what nutrients and sugars the smoothie contains. (Photo taken by Ralf Kabelitz and used under CC 3.0 Unported license)
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. In the human body, sucrose is broken down to create two different kinds of sugar: glucose and fructose. Both glucose and fructose are also commonly found in foods. 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 a digestive enzyme. Enzymes are proteins that help speed up many different chemical reactions. In the human body, the digestive enzyme that catalyzes the reaction turning sucrose into glucose and fructose 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 Equation 1.
But sucrose is not the only sugar that our bodies break down into different, more "simple" sugars. The sugar lactose can be broken down to create glucose and galactose (another sugar that is easily absorbed directly in the intestines because it is a monosaccharide). This reaction is shown in Equation 2. Lactose is a key constituent of breast milk, so it is essential that babies are able to digest it, and they do. Babies are able to digest lactose from breast milk because they make lactase, which is a digestive enzyme that catalyzes the breakdown of lactose into glucose and galactose. For reasons that are unclear, most people in the world stop producing lactase after about age 2. Once the production of lactase stops, drinking milk or eating milk products, such as cheese, can cause uncomfortable digestive problems because the lactose passes through the digestive system undigested or partially digested. This inability to digest lactose is called lactose intolerance. Overall, if someone is lactose intolerant, a very unpleasant reaction can take place in response to the presence of lactose in the digestive system, characterized by cramps, bloating, gas, and diarrhea.
However, some people are lactose tolerant, meaning they can digest dairy products. Though it might surprise you, a minority of the world's population are lactose tolerant due to a genetic change that occurred a few thousand years ago in Europe and resulted in maintaining lactase production into adulthood. Consequently, lactose tolerance is associated primarily with people whose ancestry is derived from certain parts of Europe. Most people in the United States are lactose tolerant, with 30–50 million people being lactose intolerant (of about 317 million people total).
Something you may have noticed that sucrose and lactose have in common is that they can both be broken down in the body to create glucose. Glucose is a simple sugar that is important, biologically, because it is the primary 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 and lactose, glucose is also made in the body by the breakdown of other carbohydrates, such as starch (foods that are rich in starch include bread, cereals, pasta, etcetera). Because sucrose, lactose, and carbohydrates 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 main types of diabetes: type I and type II.
In this food science project, you will investigate the concentration of glucose, sucrose, and lactose in different foods commonly used in smoothies and milkshakes, and how the conversion of sucrose and lactose to glucose (using the enzymes invertase and lactase, respectively) changes how much glucose we actually digest from these drinks. If someone has hypoglycemia and needs a fast glucose boost, you will figure out what would be the best drink to make using the ingredients you test. Which foods should be avoided? (Hint: While sucrose and lactase can be converted to glucose, this takes some time to happen, so they probably are not good to use if a fast glucose boost is needed.) If someone has type II diabetes, which foods should be eaten in moderation, not only because they are high in glucose, but also because they are high in sucrose and/or lactose? On the other hand, which foods may be safe for someone with type II diabetes to eat since 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 glucose levels (by measuring the amount of glucose in their urine). When you dip the test strip into a liquid, such as orange juice, it will change color if glucose is present. The degree of color change depends on the concentration of glucose. After you treat each food item with invertase, and then with lactase, you will be able to use the glucose test strips to figure out relatively how much glucose, sucrose, and lactose is in each ingredient and how much glucose may end up in our bodies.
What ingredients do you think could be combined to make a tasty milkshake or smoothie that does not change someone's blood levels much, if at all? What about making a delicious drink that gives someone an immediate glucose boost, or, alternatively, does not give a quick glucose boost but instead gives a glucose boost over time? Get ready to test some ingredients and design some delicious milkshake or smoothie recipes to answer these questions!
Terms and Concepts
- Lactose intolerant
- Lactose tolerant
- Blood glucose level
- Insulin resistance
- Positive control
- Negative control
- Dilution series
- What are some foods commonly used in smoothies and/or milkshakes?
- What foods commonly used in smoothies and/or milkshakes do you think have a high level of glucose? What about sucrose and lactose?
- Which foods commonly used in smoothies and/or milkshakes have low levels of glucose, sucrose, and/or lactose?
- What is the concentration range of glucose in healthy people? What is the range used to diagnose someone with diabetes?
- What is the difference between invertase and lactase? How are they similar?
- Horn, R. S. (n.d.). What is so special about carbohydrates? Medbio.info. Retrieved July 2, 2013.
- NutritionData.Self.com. (n.d.). Foods highest in sucrose. Retrieved July 2, 2013.
- NutritionData.Self.com. (n.d.). Foods highest in lactose. Retrieved July 2, 2013.
- Novo Nordisk. (2018). Diabetes care. Retrieved May 22, 2018.
- American Diabetes Association. (n.d.). Medication Management: Blood sugar. Retrieved November 5, 2020.
- Khan Academy. (n.d.). Glucose insulin and diabetes: The basics of type I and type II diabetes. Retrieved July 2, 2013.
These specialty items can be purchased from our partner Home Science Tools:
- Sugar Metabolism Kit (1). You will need the following items from the kit:
- Graduated cylinder, 100 mL (1)
- Invertase powder (1 g), makes 25 mL (2)
- Glucose powder (30 g) (1)
- Urinalysis test strips that measure glucose (100)
- Graduated transfer pipettes, 3 mL (4)
You will also need to gather these items (not included in the kit):
- Disposable cups, 8 oz. or larger (at least 25)
- Permanent marker
- Optional: Knife and spoon
- Optional: Food coloring (color does not matter)
- Spoons for stirring (at least 20; you may need to clean the spoons and reuse them during the Procedure)
- Distilled water, available at most grocery stores
- Room-temperature tap water
- Measuring spoons
- 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 down to 4 g. A digital scale accurate to at least 1 g (the Fast Weigh MS-500-BLK Digital Pocket Scale) is available from Amazon.com.
- Bottle caps (at least 5)
- Lactose (6 g); available online at Amazon.com
- Lactase drops (7 mL); available at some drug stores or grocery stores, or online at Amazon.com
- Foods to test that are common ingredients in smoothies and/or milkshakes. Try at least three different liquids and three different common additives. Here are some examples, but you may want to do some research on your own to find ingredients you would like to test:
- Common liquids: Milk, soy milk, lactose-free milk, cream, fruit juice
- Common additives: Fruits (such as strawberries, bananas, raspberries, etc.), ice cream, honey, cocoa powder, malted milk powder, peanut butter
- Blender, if testing fruits
- Lab notebook
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Testing the Glucose Strips
In this part of the science project, you will create controls, which are 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 test strips are not working properly, then the rest of this experiment will not be valid. The positive controls will contain different concentrations of glucose. The negative control will be a sample without glucose.
- First, make the positive controls using water and the glucose powder. To do this, make a dilution series using sequential twofold dilutions to create the following concentrations: 2%, 1%, 0.5%, 0.25%, 0.125%, and 0.0625%.
- Label six cups: 2%, 1%, 0.5%, 0.25%, 0.125%, and 0.0625%.
- Add 4 grams (g) of glucose to 200 mL of water in the cup labeled 2% and stir until the glucose dissolves.
- Optional: Add 2–5 drops of food color to the 2% glucose solution. The color does not matter. Note: The food coloring will allow you to keep track of your dilution levels as the color of each dilution will get less intense. It does not interfere with the glucose measurements.
- Add 100 mL of water to the other five cups.
- Measure 100 mL of the 2% solution and add it to the cup labeled 1% to make a 1% solution. Stir well.
- Measure 100 mL of the 1% solution and add it to the cup labeled 0.5% to make a 0.5% solution. Stir well.
- 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.
- Repeat this process for the remaining dilutions.
- When you are done, each cup should have 100 mL of liquid, except for the 0.0625% solution, which should have 200 mL.
- 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.
- If you used food coloring for your dilution series, you should now have seven cups that look similar to the ones in Figure 2.
Figure 2. If you used food coloring (in this picture red food coloring was used), 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. A seventh cup, serving as the negative control, should only contain water (on the far right in this picture).
- Dip a test strip into each of the seven cups, one at a time. After 1–2 seconds, remove the test strips from each solution and watch them for 30 seconds (which should be the time recommended in the test strip instructions). Then match the color of the glucose marker on the test strip to the color on the bottle shown in Figure 3. Do the colors match what you would expect? Write down your observations in your lab notebook. Note: For high glucose concentrations, it might take up to 60 seconds until the color matches the actual concentration. Therefore it is recommended that you dilute your samples once they approach a glucose concentration of 1%.
- See the Technical Note for guidance on matching the color of the glucose test strips to the color on the bottle.
- 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.
- If you do not have a clear color change for any of the positive control solutions with a concentration greater than 0.0625%, repeat the procedure. If the second time it is still problematic, you might have to buy new test strips. It is ok to have a slightly lower reading for the pure glucose solutions. Remember, these test strips were designed for measuring low concentrations of glucose in a urine sample, so the results might be slightly different for pure glucose solutions. If the test strips for the glucose solutions at 30 seconds are 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%), you could adjust the readout time accordingly (for example to 60 seconds). However, you have to make sure that throughout the experiment, you keep the same readout time for all of your samples.
- Tip: If you would like additional help with reading the glucose test strips, check out the Frequently Asked Questions (FAQ) for this science project.
When matching the color of a glucose test strip to a color on the bottle, keep these helpful tips in mind:
- 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%, 0.25%, 0.5%, 1% and 2% glucose solutions, as shown in Figure 3.
- Some test strip colors may fall between two of the colors on the bottle; for example, between 0.5% 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 Procedure, you may need to then perform a 1:10 dilution and re-test the sample. You will get more accurate results if you start diluting your samples once the glucose concentration is getting close to 1%. There are two ways in which you may perform a 1:10 dilution, and the preferred way will be specified in the text:
- Use a transfer pipette to add nine drops of water and one drop of the test solution on a bottle cap. Rinse the transfer pipette in between each sample.
- 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.
Figure 3. This is the color chart for glucose on the test strip bottle. After a glucose test strip is dipped in a glucose solution and removed, its color should change and 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 Activity of Invertase and Lactase
In this next part of the science project, you will test the activity of the invertase and lactase enzymes. It is important for you to do this step so that you know how long you should test your selected foods with the digestive enzymes. You will test the activity of the invertase enzyme by investigating how long it takes to turn a known amount of sucrose (in solution) into glucose. Similarly, you will test the activity of the lactase enzyme by investigating how long it takes to turn a certain amount of lactose (in solution) into glucose. When invertase is added to the sucrose solution, or when lactase is added to the lactose solution, the concentration of glucose should increase over time as the sugars are 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. 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 from making more product.) In this section, you will determine how much time is needed for the invertase enzyme to convert the sucrose in a 10% solution, and how much time is needed for the lactase enzyme to convert the lactose in a 10% solution.
- Make a solution containing 10% sucrose.
- Fill a cup with 60 mL of room-temperature water.
- Add 6 g of sucrose to the cup of water. Mix until all the sucrose dissolves.
- Put 15 mL (1 Tbsp) of this solution into a new cup.
- How many grams of sucrose are in 15 mL of the 10% solution?
- In your lab notebook, make a data table in which to record your data. You will be taking glucose readings over time to see how much sucrose has been converted to glucose by the invertase enzyme.
- Starting at zero, plan on taking glucose readings every 5 minutes (min) for the first 30 min, and then every 10 min after that. Plan on taking readings for 90 min total.
- Use a glucose test strip to determine the concentration of glucose in the sucrose solution, as you did in step 4 of the "Testing the Glucose Strips" section, above. Write your result in the data table in your lab notebook under "0 minutes."
- There should be 0% glucose in the sucrose solution.
- Set a timer for 90 minutes or make sure a clock is nearby.
- Get one of the bottles from the sugar metabolism kit that contains 1 g of powdered invertase and prepare it for the experiment. Note: You can prepare the invertase solution right before you start the experiment, however, the invertase works better if you prepare the solution one day in advance. You do not have to prepare both of the invertase bottles at the same time. You can keep the second bottle for future experiments or prepare it once you run out of invertase in this experiment.
- Fill the measuring cylinder with 25 mL of distilled water.
- Open the invertase bottle and add the water to the invertase powder.
- Then close the lid and shake the bottle until all the powder has dissolved.
- Important: Once rehydrated, the invertase solution needs to be kept in the refrigerator when not used.
- Add 15 drops (about 0.75 mL) of invertase to the sucrose solution. Quickly mix the solution with a clean spoon.
- Start the timer or write down the exact time in your lab notebook.
- Use the glucose test strips to take glucose readings of the solution over time, as described in step 2 of this section.
- Write your results in the data table in your lab notebook.
- See the Technical Note, above, for guidance on matching the color of the glucose test strips to the color on the test strip bottle.
- Remember that the glucose readings are most accurate if you dilute your sample once the glucose concentrations reach about 1%. 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 on the third bullet point) to determine the actual percentage of glucose in the sample. Take a glucose reading of the 1:10 dilution.
- When the glucose reading has remained the same for at least 20 min (3 readings spaced 10 min apart), you can stop taking readings.
- Now make a solution containing 10% lactose.
- Repeat step 1 using new, clean cups and lactose instead of sucrose.
- If you have trouble dissolving the lactose in the water, you could try using warmer water. Important: If you do this, be sure to let the solution cool to room temperature before testing it because temperature can affect enzyme activity.
- Test the activity of the lactase enzyme using the lactose solution by repeating steps 2–8 of this section with the following changes:
- Substitute lactase for invertase.
- Use 15 mL of the lactose solution.
- You will only need 3 drops of the lactase enzyme (as opposed to the 15 drops you used with the invertase enzyme).
- Just like the invertase enzyme solution, be sure to store the lactase enzyme in the refrigerator immediately after you are done using it.
- Optional: You may graph your results to more visually represent and analyze your data. To do this, make one graph for invertase and one graph for lactase. On both graphs, put the time on the x-axis and the glucose concentration on the y-axis.
- You should end up with graphs that roughly look similar to Figure 4, below.
Figure 4. The enzymes should initially convert the sugars 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 enzymes may still be converting some sugars to glucose, they are doing it at an extremely reduced rate. The red asterisk marks where the glucose concentration first leveled off. If you create graphs, they may only roughly match the line in this graph.
- Look at your data and figure out at what time point the enzyme activity started to level off. (Figure this out separately for each enzyme.) For example, in Figure 4, above, this point is marked with a red asterisk.
- For each enzyme, add 10 minutes onto the time you figured out in step 12 (further explained in 13.a.). Write these times down for each enzyme somewhere in your lab notebook. These are the times you will use to test your selected food items.
- At the plateau times you figured out in step 12, the enzymes should be mostly done converting the sugars to glucose, based on your data. You are adding an extra 10 minutes to this time just to make sure the enzymes are nearly completely done with this process.
Testing Smoothie and/or Milkshake Ingredients for Glucose, Sucrose, and Lactose
Now that you have determined how long it takes each enzyme to finish converting its sugar into glucose, you are ready to test your selected smoothie and/or milkshake ingredients. In this part of the science project, you will first test the glucose concentration of your selected foods. Then you will react each with invertase and, by determining how this changes their glucose concentrations, you will figure out how much sucrose was in the food. Lastly you will react the ingredients with lactase and, again by determining how this changes their glucose concentrations, you will figure out how much lactose was in the food.
- In your lab notebook, make a data table for recording your data.
- For each food sample, you will take three glucose readings: one before adding any digestive enzymes, one after adding the invertase, and one after adding the lactase.
- You will use the times you determined for each enzyme from step 13 in the "Testing the Activity of Invertase and Lactase" section, above. Specifically, after measuring the glucose of each sample, you will add the invertase to each and measure the glucose levels again after the time you determined for invertase has passed. Finally, you will add the lactase (to the same samples) and measure the glucose levels after the time has passed for lactase.
- Test at least three different samples of each selected food. You may want to test these at different times because of the amount of time the tests require.
- Multiple trials help scientists make sure that their results are accurate and reproducible.
- Label the cups with the ingredient samples you will test.
- Important: Let all of the ingredient samples you will test come to room temperature before testing them. 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 differing temperatures.
- You may need to specially prepare some of your ingredients for testing (Important: If you have to use water to make dilutions, make sure that the water is at room temperature):
- For testing viscous ingredients (like peanut butter or honey), dilute the samples 1:10 (or 10%) with water. Do this dilution using ½ tsp. of your sample (as described in the third bullet point of the Technical Note, above).
- For testing fruits, dilute the samples 1:5 (or 20%) with water and blend them in a blender. To do this you will want to weigh out the fruit to make a 1:5 dilution with enough water to blend.
- For example, you could use 47.4 g of a fruit and 237 mL (1 cup) of water. (47.4 g divided by 237 mL is 0.2, or 20%.)
- For testing powders (like malted milk powder or cocoa powder), dilute the powder 1:5 (20%) with water by dissolving 3 g in 15 mL (1 Tbsp.) water.
- To each cup, add 15 mL (1 Tbsp.) of the ingredient (diluted or undiluted) that you will test. Important: If you have to use water to make dilutions, make sure that the water is at room temperature.
- Use a glucose test strip to determine the concentration of glucose in each food sample, as you did in step 4 of the "Testing the Glucose Strips" section, above.
- See the Technical Note, above, for guidance on matching the color of the glucose test strips to the color on the bottle.
- If the color changes to the maximum range (2%) before 30 sec, list it as greater than 2% (">2%") and perform a 1:10 dilution using ½ tsp. of your sample (as described in the third bullet point of the Technical Note, above). Use the diluted sample for all tests.
- Write the glucose concentration for each sample in your data table.
- Set a timer for the time you determined for invertase (in step 13 of the previous section) or make sure a clock is nearby.
- Add 15 drops (about 0.75 mL) of invertase to each ingredient sample. Quickly mix the samples. Always be sure to use a clean, new spoon for each different solution you mix.
- Start only a few samples at a time so it is easier to manage them.
- Other than taking it out to quickly add to the samples, the rehydrated invertase solution should remain in the refrigerator.
- Start the timer or write down the exact time in your lab notebook.
- When the time you determined for the invertase enzyme has passed, use a glucose test strip to determine the concentration of glucose in each sample. Write this in your data table.
- See the Technical Note, above, for guidance on matching the color of the glucose test strips to the color on the bottle.
- If the color changes to the maximum range (2%) before 30 sec, list it as greater than 2% (">2%") and perform a 1:10 dilution using 1 drop of your test solution (as described in the third bullet point of the Technical Note, above). Take a glucose reading of the 1:10 dilution.
- After taking these glucose measurements, set a timer for the time you determined for lactase (in step 13 of the previous section) or have a clock nearby.
- Then add 3 drops of lactase to each ingredient sample. Quickly mix the samples.
- Again, like the invertase, the lactase solution should remain in the refrigerator when it is not being used.
- Start the timer or write down the exact time in your lab notebook.
- When the time you determined for the lactase enzyme has passed, repeat step 11 to determine the glucose concentration in each sample.
- If you did not test all of your ingredients at the same time (or three different samples of each ingredient), you will want to repeat this process (steps 2–15) until you have tested all of them.
- You may want to test these at different times because of the amount of time the tests require.
- Graph your results. Make a bar graph and put the ingredient names of the samples on the x-axis and glucose concentration on the y-axis. Include all three glucose readings for each sample (before adding enzymes, after adding invertase, and after adding lactase); to do this, it may be easiest to cluster the three bars for each ingredient sample.
- Tip: If you diluted any of your samples when testing them, be sure to account for this in your graphs. The graphs should show the undiluted glucose concentrations.
Analyzing Your Results and Testing Smoothie and/or Milkshake Recipes
In this part of the science project, you will analyze your data, determine how much of the different sugars (glucose, sucrose, and lactose) are in each ingredient you tested, and come up with your own smoothie and/or milkshake recipes to give someone a high or low dose of glucose.
- Look at the graph you made in step 17 of the "Testing Smoothie and/or Milkshake Ingredients for Glucose, Sucrose, and Lactose" section. Do the glucose readings you took before adding the digestive enzymes match what you would expect for these foods? What about after adding each enzyme?
- Hint: Remember that invertase converts sucrose to glucose, so if you saw more glucose after adding invertase, then the ingredient had sucrose in it. Likewise, since lactase converts lactose to glucose, if you saw more glucose after adding lactase, then the ingredient most likely had lactose in it.
- Which ingredients had the most glucose before adding the enzymes? Which had the least? Did any have no glucose?
- Based on any change in glucose levels after adding invertase, which ingredients had the highest sucrose concentration, and which had the lowest? Did any foods have no sucrose? Do your results match your predictions?
- What about the lactose levels? Based on any change in glucose levels after adding lactase, which ingredients had the highest and lowest lactose concentrations? Do your results match your predictions?
- Note: If you saw a slight increase in glucose after adding the lactase enzyme and this was completely unexpected, this could be because the sample had a large amount of sucrose and the invertase is still converting sucrose to glucose, though at an extremely reduced rate. To check for this, you could re-test the ingredient but this time use a greater dilution (at least 1:5).
- Overall, after adding both enzymes, which food ingredients had the largest amounts of glucose? Which had the least?
- How do your results compare to the amount of sugar listed for these foods on their packaging?
- 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.
- Note: If you want to determine the actual sucrose and lactose concentrations in the ingredients you tested, see the Make It Your Own section for how to do this. For this science project, only the relative concentrations are being analyzed.
- 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 due to other chemical reactions taking place? Hint: Re-read the Introduction.
- 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 ingredients would you recommend he or she eat? Which ingredients would you recommend avoiding? Which ingredients would you recommend he or she uses in moderation, not only because they are high in glucose, but also because they are high in sucrose and/or lactose? Which foods may be safe for someone with diabetes to consume because they do not change blood glucose levels that much?
- Think about your answers to step 4 of this section, and devise three different smoothie and/or milkshake recipes, as described below. Include at least two or three ingredients in each milkshake (at least one liquid and one additive). The ratio of ingredients you use is up to you! Then make your drinks and test them (only 15 mL each) as you did in the "Testing Smoothie and/or Milkshake Ingredients for Glucose, Sucrose, and Lactose" section above. Do your predictions match your results? Which drinks would be best for each type of medical condition or situation? For what medical situation would some of these drinks not be good to use?
- Make one milkshake or smoothie that should not change blood glucose levels much (if at all).
- Make a second milkshake or smoothie that should give someone a fast glucose boost.
- Make a third milkshake or smoothie that should not give much (if any) fast glucose boost, but will give a person a glucose boost over time.
For troubleshooting tips, please read our FAQ: Lactose, Sucrose, and Glucose: How Many Sugars are in Your Smoothie?.
Ask an Expert
- In this science project you determined the relative concentration of sucrose and lactose in each ingredient you tested. You could also try to calculate the actual concentrations, but this is more challenging. If you want to figure out how to do this, see the Procedure of the science project Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food. Specifically, read about the linear time point (discussed around Figure 4) and then go to the section on "Analyzing Your Results" and look at step 2. The most accurate way to calculate product concentrations based on enzyme activity is using the linear time point, as discussed in that science project idea, but in the current science project idea you can get a rough idea of the actual sucrose and lactose concentrations in your ingredients by using the time points you arrived at to take the glucose measurements. Keep in mind that this should be when the enzyme has reached a plateau of converting the sugars (sucrose or lactose) to glucose (not when only half is converted). Are the actual concentrations of sucrose and lactose what you would expect for the different ingredients?
- When a person with diabetes has low blood glucose, he or she needs to eat or drink something with glucose in it right away. How much of the different ingredients 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 or lactose to be converted into 4 g of glucose? Tip: Keep in mind that since 2 g of glucose in 100 mL of water would give a 2% glucose reading, 0.3 g in 15 mL would likewise give a 2% reading. You can find out more about blood sugar levels after eating a meal by watching this video: Blood sugar levels.
- Enzyme activity can be significantly affected by pH. Pick an ingredient you tested that had a lot of sucrose or lactose, or just use a sucrose or lactose solution, and add an acid or a base to make it more acidic or more basic. Check the pH of the solutions using pH test strips and then test the invertase or lactase (or both, as you did in this science project) activity in each. At which pH did the enzyme(s) work best? Which pH was worst? How might this have affected your results in this science project? For more information on acids, bases, and pH, see Acids, Bases, & the pH Scale. Alternatively, you could try varying the temperature, which can also affect enzyme activity.
- In this science 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 science project more similar to what happens in the human digestive system?
- Do some research on foods that people who are lactose intolerant should avoid, and then compare them with your results. Based on your results, can you figure out how little lactose is needed to trigger an unpleasant digestive response in most people who are lactose intolerant? Are you surprised by your results? In other words, is more or less lactose than you expected needed for such a response?
- Can you make the smoothie and/or milkshake recipes you devised at the end of this science project healthier, perhaps with less fat and/or fewer calories?
- For similar science projects on glucose, sucrose, and/or lactose, see:
- Sucrose & Glucose & Fructose, Oh My! Uncovering Hidden Sugar in Your Food.
- For a less-advanced science project, see I Love Ice Cream, But It Doesn't Love Me: Understanding Lactose Intolerance.
- For a less-advanced science project, see How Sweet It Is! Measuring Glucose in Your Food.
Frequently Asked Questions (FAQ)
- If you let the invertase or lactase enzymes sit out at room temperature long, this can quickly decrease their activity. Enzymes naturally degrade over time, but keeping them cool helps to prevent them from degrading. Always keep the invertase and lactase enzymes in the refrigerator when you are not using them, 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% lactose and sucrose solutions you made) were not at room temperature. The activity of enzymes is affected by temperature, so if the temperature of your sugar solutions and ingredients was not consistent (or, similarly, the water you used in your dilutions was not at room temperature), the enzymes 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 solutions, 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.
- Some foods contain compounds that can interfere with the chemical reactions that occur on the glucose test strips to change their color. Ascorbic acid (Vitamin C) is one example that is known to cause low glucose readings if present in high concentrations.
- 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 Procedure and Technical Note for how to do this. If you do not do this, your results may be lower than expected.
If you like this project, you might enjoy exploring these related careers:
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