Section 2: Resources

Reinforcement Activity

Learning about Preservatives: Bakery Bread Versus Store Bought Bread

By comparing slices of store-bought bread containing preservatives to bread from a bakery that contains no preservatives, children learn about the role of preservatives in food and how they act to slow down decomposition.

Ask students if they have heard of preservatives and if they know what preservatives do in food. Explain that some food is prepared without preservatives, such as bread from a bakery or bread made at home. Tell students that in order to see how preservatives work, they will be testing out the differences between bread with and without preservatives. Discuss the importance of treating both kinds of bread the same in this experiment.

Ask students to make predictions about what will happen to both kinds of bread when moistened and sealed in a bag. Record their predictions. Proceed with the experiment by giving each student or each group of students a slice of store bought bread and bakery bread. Be sure to check the ingredients of the store bought bread to make certain that it contains preservatives. Likewise, inquire about the ingredients of the bakery bread to be certain that it does not contain preservatives. Using a water dropper, have the students dot both pieces of bread with 10 drops of water, reminding students to be careful to drop the same amount of water on each slice of bread. Seal each slice of bread in its own plastic resealable bag. Direct them to put a piece of masking tape on the outside of the bag and write their name on it, and to label each bag as "preservatives" or "no preservatives" accordingly. In order to help students not to mix up the breads, hand out one type of bread at a time and go through all the steps with that bread first. Once it is sealed and labeled, proceed with the other type of bread. The bags should be pinned up (on the very top edge of the bag so as not to puncture the sealed part) or taped up in a place that does not receive direct sunlight. A hallway is an excellent choice as long as the bags are pinned up high enough so that students unfamiliar with the project will not open them. Tell the students not to open them.

Every few days, have students observe their bread samples (through the bag, they should not open it) carefully with hand lenses and describe what they see. They should record their observations in a journal, by describing what they see and/or drawing pictures. Ask students to think about how what is happening to the two slices of bread is similar and how it is different, and to think about the role of the preservatives in what is happening. After approximately 2-3 weeks (or whenever there is sufficient mold growth on the bread), review the students' predictions and observations, and discuss the effect of preservatives and no preservatives on the bread samples. Students should understand how preservatives relate to decomposition and how they slow down the rate of microbe growth. Ask students to think about why people put preservatives in food, particularly food that is made and shipped to stores where it sits on a shelf waiting to be bought. Ask them to consider the pros and cons of adding preservatives.