Iki indicator

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Experiment 1: Enzymes in Food

Amylase is used by humans to facilitate digestion. Specifically, it is an enzyme that breaks down starch molecules into glucose 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 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).

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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., sweet potato, apple, potato, corn, etc.)

*Ginger Root *Kitchen Knife *Paper Towels (non-starch containing) *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. Use a permanent marker to create four quadrants of equal size by drawing two perpendicular lines that intersect in the center of the paper towel (Figure 3).

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Figure 3: Paper towel set-up.

4. Spray the sectioned paper towel and another blank paper towel with the starch solution. Allow the starch to dry for approximately one hour (this time interval may vary by location).

5. Once the paper towels are completely dry, label the blank paper towel “saliva” and set it aside to be used in Step 14.

6. Use the permanent marker to label the top left quadrant of the sectioned paper towel “positive control” and the top right quadrant “negative control”.

7. Select two food items from your kitchen cabinet or refrigerator, and obtain a fresh ginger root sample.

Note: If ginger root is not available, use banana as a positive control. Be sure to adjust data tables and labels accordingly.

8. Obtain a kitchen knife and a cutting board. Carefully cut your two selected food items and the ginger root to expose the internal surfaces. Clean or rinse the knife between cuts.

9. Set up a positive control for this experiment. Use the permanent marker to add the label “ginger root” under the positive control label. Carefully rub an area in the positive control quadrant with the fresh surface of the ginger root (which is known to contain amylase). Ensure a good application by firmly pressing the exposed surface of the root onto the paper towel. Let the area rest.

10. Set-up a negative control for this experiment in the “negative control” quadrant. Use your knowledge of the scientific method and experimental controls to establish this component. Identify your negative control in Table 1.

Hint: What result would you expect if amylase was not present when tested with IKI solution?

11. Use the permanent marker to label the bottom two quadrants with the name of the two food items you chose to test for amylase.

12. Carefully, but firmly, rub the fresh/exposed area of the food items on the paper towel in their designated quadrants back and forth 10 - 15 times.

13. Allow the areas to dry for at least five minutes.

14. While you wait, provide a saliva sample by spitting into the center of the paper towel labeled “saliva” that you prepared with starch in Step 5. Spread the saliva out by gently rubbing the halves of the paper towel together.

15. After your food samples and controls have rested for at least five minutes, test them with IKI solution.

Note: Use caution when spraying the IKI solution. Hold the IKI spray bottle 25 - 30 cm away from the paper towel, and mist the IKI solution over each quadrant.

16. Allow the IKI solution to dry. Observe where and what 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: Ginger Root

Negative Control: Student Must Select

Food Product:

Food Product:

Saliva:

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 infant’s 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 don’t these enzymes digest the stomach and small intestine, which are partially composed of protein?

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