Enzymes

Experiment 1: Enzymes in Food

This experiment tests for the presence of amylase in food by using Iodine-Potassium 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).

concept_tab_2

Materials

(1) 2 oz. Bottle (Empty) (1) 100 mL Graduated Cylinder 30 mL Iodine-Potassium Iodide, IKI Permanent Marker Ruler 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

Procedure:

1. Remove the cap from the starch solution. Attach the spray lid to the starch solution.

2. 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.

3. 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).

4. 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.

5. 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.

6. Select two food items from your kitchen cabinet or refrigerator.

7. Obtain a kitchen knife and a cutting board. Carefully cut your selected food items to create a fresh surface.

Figure 3: Sample set-up.

Figure 3: Sample set-up.

8. Gently rub the fresh/exposed area of the food items on the dry, starch-sprayed paper towel back and forth 10 – 15 times. Label where each specimen was rubbed on the paper towel with a permanent marker (Figure 3).

9. Wash your hands with soap and water.

10. Take your finger and place it on your tongue to transfer some saliva to your finger. Then, rub your moistened finger saliva into the paper towel. Repeat this step until you are able to adequately moisten the paper towel. Note: You should always wash your hands before touching your tongue! Alternatively, if you do not wish to put your hands in your mouth, you may also 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.

11. Wait five minutes.

12. Hold the IKI spray bottle 25 – 30 cm away from the paper towel, and mist with the IKI solution.

13. 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

Substance

Resulting Color

Presence of Starch?

Positive Control: Starch

Dark Purple

Yes

Negative Control : Cellulose

Brownish red color

No

Food Product: Apple

Dark Purple

yes

Food Product: Potato

Dark Purple

yes

Saliva: Amylase

Brownish red color