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Sue Balala
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Have you ever noticed the warning on a JELL-O package not to use fresh or frozen pineapple? Today we are going to put the fruit into gelatin and see what happens. What are some possible results?

BACKGROUND: The enzymes in some tropical fruits can break down
protein. For example meat tenderizers have the enzyme, papain,
that breaks down some of the fiber. We use it to soften up a
tough piece of meat. The papain comes from the papaya fruit.
Pineapple has a digestive enzyme called bromelin.

MATERIALS: Four Test Tubes Fresh Pineapple
Hot Gelatin Canned Pineapple
Ice Water Bath Frozen Pineapple
Glass Marker Single-edged Razor Blade
Test Tube Rack

l. With the razor blade carefully cut equal sized pieces of fresh canned, and frozen pineapple.
The pieces should be just small enough to slide into your tubes.

2. Label the test tubes l-4.

3. Pour 3 ml of liquid gelatin into each of the four tubes.

4. Place the different pieces of pineapple into the first three tubes.
See the table below to match up the contents. Notice that test tube #4 contains only gelatin.

5. Mix the contents of the tubes by rolling them upright betweenthe palms of your hands.

6. Place all four test tubes into the ice water bath.

7. Every few minutes check to see if the gelatin is setting in the tubes. When test tube#4 has gelled firmly you can remove all the tubes and compare the consistencies

8. Record you observations in the table below.


1. Gelatin and Fresh Pineapple

2. Gelatin and Canned Pineapple

3. Gelatin and Frozen

4. Gelatin


1. Why did test tube #4 contain only gelatin?

2. What could account for the different results in the tubes?

3. How could the canning process change bromelin?

4. What could you do to fresh pineapple that would allow the salad to gel?

5. Design an experiment to find a temperature at which a meat tenderizer works the best?

We usually do this lab when we are discussing digestive enzymes and temperature dependence of enzymes. The students like the application of biochemistry to something they eat.

Here are some suggestions that have helped make the lab more smoothly.
Preparing the gelatin: Stir two envelopes of KNOX unflavored gelatin into 800 ml of hot water. This should be plenty for three classes. Store it in a warm water bath when the students are using it so it will pour easily.

Remind the students to rinse of the razor blade between types of pineapple. Clean up is easier if they cut the fruit on paper plates.

Canned Pineapple: Use the chunky style.

Fresh Pineapple: You will probably have to buy a whole pineapple and most of it will be left after the labs. You and the students might enjoy eating it.

Ice baths made in beakers or cans will eliminate too much movement through the room.

The name of the digestive enzyme you were working with is bromelin. It is named after the group of plants to which the pineapple belongs - the Bromeliads.

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