Enzymes in Food...


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Experiment 1: Enzymes in Food
Amylase is used by humans to facilitate digestion. Specifically, it is an enzyme
which breaks down starch molecules into sugar molecules. This is why people
sometimes observe a sweet taste after sucking on a starch-containing food for
an extended period of time. Amylase is found naturally in human saliva and
the pancreas. However, it is also present in some of the common plant foods
consumed by humans.
This experiment tests for the presence of amylase in food by using IodinePotassium Iodide, IKI. IKI is a color indicator used to detect starch. This
indicator turns dark purple or black in color when in the presence of starch.
Therefore, if the IKI solution turns to a dark purple or black color during the
experiment, one can determine that amylase is not present (because
presence of amylase would break down the starch molecules, and the IKI
would not change color).
(1) 2 oz. Bottle (Empty)
(1) 100 mL Graduated
30 mL Iodine-Potassium
Iodide, IKI
Permanent Marker
2 Spray Lids
30 mL Starch (liquid)
*Cutting Board
*2 Food Products (e.g., ginger
root, apple, potato, etc.)
*Kitchen Knife
*Paper Towel
*Saliva Sample
*Tap Water
*You Must Provide
Remove the cap from the starch solution. Attach the spray lid to the
starch solution.
Rinse out the empty two ounce bottle with tap water. Use the 100 mL
graduated cylinder to measure and pour 30 mL of IKI into the empty two
ounce bottle. Attach the remaining spray lid to the bottle.
Set up a positive control for this experiment by spraying a paper towel
with the starch solution. Allow the starch to dry for approximately one
hour (this time interval may vary by location).
In the mean time, set up a negative control for this experiment. Use your
knowledge of the scientific method and experimental controls to
establish this component (hint: what should happen when IKI solution
contacts something that does not contain starch?) Identify your negative
control in Table 1.
Note: Be sure to space the positive and negative controls apart from
each other to prevent cross-contamination.
When the starch solution has dried, test your positive and negative
controls. This step establishes a baseline color scale for you to evaluate
the starch concentration of the food products you will test in Steps 7 11. Record your results in Table 1.
Select two food items from your kitchen cabinet or refrigerator.
Obtain a kitchen knife and a cutting board. Carefullycut your selected
food items to create a fresh surface.
Figure 3: Sample set-up.
Gently rub the fresh/exposed area of the food items on the dry, starchsprayed paper towel back and forth 10 - 15 times. Label where each
specimen was rubbed on the paper towel with a permanent marker
(Figure 3).
Provide a saliva sample by spitting in a separate bowl and rubbing the
paper towel in the saliva. Be sure not to spit on the paper towel directly
as you may unintentionally cross-contaminate your samples. Repeat
this step until you are able to adequately moisten the paper towel.
Wait five minutes.
Hold the IKI spray bottle 25 - 30 cm away from the paper towel, and
mist with the IKI solution.
The reaction will be complete after approximately 60 seconds. Observe
where color develops, and consider what these results indicate. Record
your results in Table 1.
Table 1: Substance vs. Starch Presence
Resulting Color
Presence of
Positive Control: Starch
Negative Control: Student Must Select
Food Product
Food Product
experiment 2: Effect of Temperature on Enzyme Activity
Figure 4: Catalase catalyzes
the decomposition of
hydrogen peroxide to water
and oxygen.
Yeast cells contain catalase, an enzyme which helps convert hydrogen
peroxide to water and oxygen. This enzyme is very significant as hydrogen
peroxide can be toxic to cells if allowed to accumulate. The effect of catalase
can be seen when yeast is combined with hydrogen peroxide (Catalase: 2
H2O2 2 H2O + O2).
In this lab you will examine the effects of temperature on enzyme (catalase)
activity based on the amount of oxygen produced. Note, be sure to remain
observant for effervescence when analyzing your results.
(2) 250 mL Beakers
3 Balloons
30 mL 3% Hydrogen
Peroxide, H2O2
Measuring Spoon
Permanent Marker
3 Test Tubes (Glass)
Test Tube Rack
Yeast Packet
*Hot Water Bath
20 cm String
*You Must Provide
Use a permanent marker to label test tubes 1, 2, and 3. Place them in
the test tube rack.
Fill each tube with 10 mL hydrogen peroxide. Then, keep one of the test
tubes in the test tube rack, but transfer the two additional test tubes to
two separate 250 mL beakers.
Find one of the balloons, and the piece of string. Wrap the string around
the uninflated balloon and measure the length of the string with the
ruler. Record the measurement in Table 2.
Create a hot water bath by performing the following steps
Determine if you will use a stovetop or microwave to heat the
water. Use the 100 mL graduated cylinder to measure and pour
approximately 200 mL of water into a small pot or microwave-safe
bowl (you will have to measure this volume in two separate
If using a stovetop, obtain a small pot and proceed to Step 4c. If
using a microwave, obtain a microwave-safe bowl and proceed to
Step 4e.
If using a stove, place a small pot on the stove and turn the stove
on to a medium heat setting.
Carefully monitor the water in the pot until it comes to a soft boil
(approximately 100 C). Use the thermometer provided in your lab
kit to verify the water temperature. Turn the stove off when the
water begins to boil. Immediately proceed to Step 5.
CAUTION: Be sure to turn the stove off after creating the hot
water bath. Monitor the heating water at all times, and never
handle a hot pan without appropriate pot holders.
If using a microwave, place the microwave-safe bowl in the
microwave and heat the water in 30 second increments until the
temperature of the water is approximately 100 C. Use the
thermometer provided in your lab kit to verify the water
temperature. Wait approximately one minute before proceeding to
Step 5.
Place Tube 1 in the refrigerator. Leave Tube 2 at room temperature, and
place Tube 3 in the hot water bath.
Important Note: The water should be at approximately 85 C when you
place Tube 3 in it. Verify the temperature with the thermometer to
ensure the water is not too hot! Temperatures which exceed
approximately 85 C may denature the hydrogen peroxide.
Record the temperatures of each condition in Table 2. Be sure to
provide the thermometer with sufficient time in between each
environment to avoid obscuring the temperature readings.
Let the tubes sit for 15 minutes.
During the 15 minutes prepare the balloons with yeast by adding tsp.
of yeast each balloon. Make sure all the yeast gets settled to the bulb of
the balloon and not caught in the neck. Be sure not spill yeast while
handling the balloons.
Carefully stretch the neck of the balloon to help ensure it does not rip
when stretched over the opening of the test tube.
Attach the neck of a balloon you prepared in step 8 to the top of Tube 2
(the room temperature test tube) making sure to not let the yeast spill
into the test tube yet. Once the balloon is securely attached to the test
tube lift the balloon and allow the yeast to enter the test tube. Tap the
bulb of the balloon to ensure all the yeast falls into the tube.
As quickly and carefully as possible remove the Tube 1 (cold) from the
refrigerator and repeat steps 9 - 10 with Tube 1 using a balloon you
prepared in step 8.
As quickly and carefully as possible remove Tube 3 (hot) from the hot
water bath and repeat steps 9 - 10 with Tube 3 using a balloon you
prepared in step 8.
Swirl each tube to mix, and wait 30 seconds.
Wrap the string around the center of each balloon to measure the
circumference. Measure the length of string with a ruler. Record your
measurements in Table 2.
Table 2: Balloon Circumference vs. Temperature
1 - (Cold)
2 - (RT)
(Uninflated, cm)
(Final, cm)
3 - (Hot)
To conduct your laboratory exercises, use the Laboratory Manual located under
Course Content. Read the introduction and the directions for each exercise/experiment
carefully before completing the exercises/experiments and answering the questions.
Save your Lab 4 Answer Sheet in the following format: LastName_Lab4 (e.g.
You should submit your document as a Word (.doc or.docx) or Rich Text Format
(.rtf) file for best compatibility.
Pre-Lab Questions
1. How could you test to see if an enzyme was completely saturated during an experiment?
2. List three conditions that would alter the activity of an enzyme. Be specific with your
3. Take a look around your house and identify household products that work by means of an
enzyme. Name the products, and indicate how you know they work with an enzyme.
Experiment 1: Enzymes In Food
Data Tables and Post-Lab Assessment
Table 1: Substance vs. Starch Presence
Resulting Color
Presence of Starch?
Positive Control: Starch
Negative Control: Student Must
Food Product
Food Product
Post-Lab Questions
1. What were your controls for this experiment? What did they demonstrate? Why was
saliva included in this experiment?
2. What is the function of amylase? What does amylase do to starch?
3. Which of the foods that you tested contained amylase? Which did not? What
experimental evidence supports your claim?
4. Saliva does not contain amylase until babies are two months old. How could this affect
an infants digestive requirements?
5. There is another digestive enzyme (other than salivary amylase) that is secreted by the
salivary glands. Research to determine what this enzyme is called. What substrate does it
act on? Where in the body does it become activated, and why?
6. Digestive enzymes in the gut include proteases, which digest proteins. Why dont these
enzymes digest the stomach and small intestine, which are partially composed of protein?
Experiment 2: Effect of Temperature on Enzyme Activity
Data Tables and Post-Lab Assessment
Table 2: Balloon Circumference vs. Temperature
Temperature (C)
(Uninflated, cm)
1 - (Cold)
2 - (RT)
3 - (Hot)
Post-Lab Questions
1. What reaction is being catalyzed in this experiment?
2. What is the enzyme in this experiment? What is the substrate?
Balloon Circumference
(Inflated, cm)
3. What is the independent variable in this experiment? What is the dependent variable?
4. How does the temperature affect enzyme function? Use evidence from your data to support
your answer.
5. Draw a graph of balloon diameter vs. temperature. What is the correlation?
6. Is there a negative control in this experiment? If yes, identify the control. If no, suggest how
you could revise the experiment to include a negative control.
7. In general, how would an increase in substrate alter enzyme activity? Draw a graph to
illustrate this relationship.
8. Design an experiment to determine the optimal temperature for enzyme function, complete
with controls. Where would you find the enzymes for this experiment? What substrate would
you use?


Solution ID:351058 | This paper was updated on 26-Nov-2015

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