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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...