Instructor Side
JCE Classroom Activity: #17
Soup or Salad? Investigating the Action of Enzymes in Fruit on Gelatin Erica Jacobsen, Journal Editorial Staff
fold here and tear out
About the Activity Most enzymes are proteins that have evolved to function as catalysts for chemical reactions in living systems. Some fruits contain proteases, a group of enzymes that catalyze the cleavage of peptide linkages in proteins. This can have an undesired effect in a gelatin salad containing fruit, because proteases in the fruit can cleave the proteins that make up the structure of gelatin so that it will not set. This is the reason for the warning on many gelatin packages “Do not use with fresh or frozen pineapple.” Other fruits may also be included in the warning. Fresh pineapple, papaya, kiwi, and figs contain the proteases bromelain, papain, actinidin, and ficin, respectively. When the enzymes are denatured, which can result from heating during the canning process, they lose their ability to cleave proteins. In this activity, students observe gelatin samples treated with substances that may or may not have an enzymatic effect on the protein in the gelatin. Substances used are fresh pineapple, canned pineapple, fresh pineapple that has been frozen and microwaved, and meat tenderizer. If the cost of fresh pineapple is prohibitive, kiwi can be substituted. Canned kiwi is uncommon, so cup #4 could be omitted. One four-serving package of gelatin makes approximately 16 ounces when prepared according to package directions. This divides well into six 3-oz. paper or plastic cups filled 3/4 full, with a small amount left over. When food is used in the lab, there is temptation for students to taste or eat it. If the activity is done in a kitchen setting using clean kitchen containers and utensils, students may eat the gelatin and fruit after completing their observations. If the activity is done in a chemistry laboratory or with glassware and other items used previously in the lab, students should not taste or eat any of the items.
Integrating the Activity into Your Curriculum Enzyme kinetics experiments are commonly done in undergraduate chemistry and biochemistry courses (1, 2). This activity introduces enzymes on a simpler, hands-on level and emphasizes the fact that we come into contact with chemistry on an everyday basis. Students often encounter items that illustrate the action of enzymes. For example, enzymes are commonly found in food products. Other enzyme activities with food include tasting the difference between ripe papaya seeds with and without their gelatinous coating (3) and curdling milk with rennin (4, 5). This activity could be used as a cross-curricular activity with a life skills class. An advanced version of this activity tests the effect of pH and enzyme inhibitors (6). The activity also provides an entry point into the science of HIV. A current treatment uses proteases to help stop the spread of HIV particles to other cells in a body infected with HIV (7 ).
perforated
Answers to Questions 1. In cups containing meat tenderizer, fresh pineapple, and frozen pineapple the gelatin surface is watery. There may be a deepening outline of the pineapple chunk where the gelatin is breaking down. In the cups that contain only gelatin and gelatin with canned pineapple and microwaved pineapple, the gelatin surface remains firm. 2. The canning process involves heating. Heat denatures the enzyme that would break down the gelatin structure. 3. Heating pineapple in the microwave has the same effect as canning: it denatures the enzyme. 4. Freezing the fresh pineapple does not denature the enzyme and therefore does not change its effect on the gelatin. 5. Meat tenderizer contains a protease that breaks down protein in the meat fibers. 6. Gelatin, meat, and the residue on contact lenses all contain protein. 7. The enzyme in the pineapple can break down proteins in skin, causing irritation. 8. If fresh or frozen pineapple is added to gelatin before it has set, the gelatin will not set when it is chilled. Fresh pineapple contains an enzyme that breaks down the structure of gelatin. You can use cooked or canned pineapple in gelatin because the enzyme is deactivated by heating.
References, Additional Information, and Related Activities 1. Hamilton, T. M.; Dobie-Galuska, A. A.; Wietstock, S. M. J. Chem. Educ. 1999, 76, 642–644. 2. Cornely, K.; Crespo, E.; Earley, M.; Kloter, R.; Levesque, A.; Pickering, M. J. Chem. Educ. 1999, 76, 644–645. 3. Tang, C. J. Chem. Educ. 1970, 47, 692. 4. Alyea, H. N. J. Chem. Educ. 1958, 35, A172. 5. Rennin is available in supermarkets under the trade name Junket. It is used in making ice cream, jelly, and cheese. 6. Reigh, D. L. J. Chem. Educ. 1976, 53, 386. 7. Jacobsen, E.; Jacobsen, J. J.; Wright, J. M. HIV-1 Protease: An Enzyme at Work. J. Chem. Educ. Software 1996, SP13. More about Enzymes: How Do Enzymes Work?: http://raven.umnh.utah.edu/new/projects/pineapple/expert.html (accessed Mar 1999) • Enzyme Labs Using Jello: http://www.woodrow.org/teachers/bi/1991/enzymes.html (accessed Mar 1999).
This Activity Sheet may be reproduced for use in the subscriber’s classroom. JChemEd.chem.wisc.edu • Vol. 76 No. 5 May 1999 • Journal of Chemical Education
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JCE Classroom Activity: #17
Student Side
Soup or Salad? Investigating the Action of Enzymes in Fruit on Gelatin Erica Jacobsen, Journal Editorial Staff Most enzymes are proteins that function as catalysts for chemical reactions in living systems. Like all catalysts, enzymes increase the rate of a reaction. Without an enzymatic catalyst, many important chemical reactions in living systems would not be completed within days or even years, and most organisms—including people—could not survive. One type of enzyme is a protease. Proteases catalyze reactions that break down (or cut apart) certain protein molecules. Some fruits contain proteases; for example, pineapple, papaya, kiwi, and figs contain the proteases bromelain, papain, actinidin, and ficin, respectively. Since gelatin contains a network of protein molecules, the preparation of a gelatin–fruit salad offers the opportunity to observe the action of a protease. Will fruit containing a protease break down the gelatin to form something more like fruit soup than fruit salad? Can anything be done to the fruit to denature (or disrupt) the protease so that it no longer functions?
Try This
CAUTION: If you are working in a chemistry laboratory, or using any glassware or other equipment from a laboratory, do not taste or eat any of the items used.
You will need: A four-serving package of any brand of flavored or unflavored gelatin, water, mixing bowl, spoon, measuring cup, toothpicks, marker, six small cups, meat tenderizer, fresh pineapple, canned pineapple chunks, and access to a microwave oven, freezer, and refrigerator. __ 1. Label the cups with the numbers 1 through 6. __ 2. Prepare the gelatin according to the directions on the package (either the quick-set method or regular method). Divide the gelatin into six equal portions in the six small labeled cups. Allow the gelatin to set or solidify in the refrigerator. You can speed up the process by placing the cups in the freezer. __ 3. Place a piece (about a 1-inch cube) of fresh pineapple in the freezer for 30 minutes. Microwave another piece of fresh pineapple of about the same size on the oven’s highest setting for one minute. Allow both pieces of pineapple to return to room temperature. __ 4. Remove the cups from the refrigerator after the gelatin has set. You can test to see if it has set by poking the surface with a toothpick. __ 5. Place the following on the surface of the gelatin in each of the cups: Cup 1: add nothing Cup 2: sprinkle a spoonful of meat tenderizer Cup 3: a piece (about 1-inch cube) of fresh pineapple Cup 4: a chunk of canned pineapple Cup 5: the piece of pineapple microwaved in step 3 Cup 6: the piece of pineapple frozen in step 3 __ 6. Examine the cups every five minutes. Push each piece of pineapple aside with a toothpick to observe its effect on the gelatin, then return the piece to its original position. Record your observations. After 15 minutes (three sets of observations), return the cups to the refrigerator. Make a final observation an hour or two later, or the next day. After completing your observations, ask your instructor what to do with the fruit and gelatin.
Questions __ 1. Summarize in a table your observations of the gelatin in each of the cups. __ 2. What does the canning process do to the pineapple? __ 3. Does microwaving the pineapple for a short time have the same effect as the canning process? Why/why not? __ 4. Does freezing the fresh pineapple make any change in its effect on the gelatin? Why/why not? __ 5. Based on your observations, how do you think meat tenderizers work? __ 6. Soft contact lens cleaners contain proteases. How is the residue on contact lenses similar to gelatin and meat? __ 7. Your mouth may become irritated after eating fresh pineapple. What is a possible chemical reason for this irritation? __ 8. Many gelatin labels list the warning “Do not use with fresh or frozen pineapple.” Imagine you work at the gelatin company and a consumer writes to you asking about the reason for the warning. Write a response to the consumer that describes the effect of fresh and frozen pineapple on gelatin and a brief explanation of the chemistry behind it.
Information from the World Wide Web 1. You Can & Gelatin (Where does gelatin come from?): http://www.youcan.com/jello/jello.html (accessed Mar 1999). 2. Bromelain Enzyme: http://www.deerland-enzymes.com/bromelain.htm (accessed Mar 1999). 3. How to Grow Pineapple: http://agrss.sherman.hawaii.edu/pineapple/pinegrow.htm (accessed Mar 1999). This Activity Sheet may be reproduced for use in the subscriber’s classroom. 624B
Journal of Chemical Education • Vol. 76 No. 5 May 1999 • JChemEd.chem.wisc.edu
