How Does the Ability of Calcium Propionate to Inhibit Bread Mold differ with Types of Bread Flours?

Category: Biology—Food Science

Project Idea by: Alana Davicino and Arielle Lewen

Fungi are single-celled or multicellular organisms that obtain food by the direct absorption of nutrients. Fungi include such things as mushrooms, athlete's foot, and mold. Mold is a fungus that produces a fuzzy, cobweblike growth on moist materials, including food. Black bread mold, Aspergillus niger, is one of the most familiar molds. This mold begins as a microscopic, airborne spore (a reproductive cell) that germinates (begins to grow) on contact with the moist surface of a food source, such as bread. It spreads rapidly, forming a netlike mass called mycelia (fungal bodies). Mycelia are tangled masses of threadlike structures called hyphae. (The singular form of mycelia is mycelium.) Spores are produced at the top of hyphae. The spores are stored in cases. When the cases break, hundreds of spores that are small and easily carried by any air movement are released. If the spores land in a suitable place, they grow and the cycle begins again.

Molds must have a warm, moist environment, oxygen, some light, and food to produce their spores. Most molds grow well on starchy foods (bread), the rind of some fruit (lemons and oranges), and materials high in cellulose, such as wood, hay, and paper products such as cardboard.

Food preservatives, such as calcium propionate in breads, inhibit the growth of mold. Breads are made from different kinds of flour, including rye, wheat, and corn. A project question might be, "What effect does the type of flour have on the ability of calcium propionate to inhibit bread mold?"

Clues for Your Investigation

Design a method of testing different kinds of bread made with different kinds of flour. All the breads should have the mold-inhibiting additive calcium propionate. The most common bread is made with white flour, so you could use this as a control. One way of testing the bread is to place a moistened paper towel inside a 1-gallon plastic reseal-able bag. Cut equal-sized pieces of each of the types of bread and place them side by side on top of the moistened paper inside the plastic bag. Close the bag and seal it with tape to prevent the bag from being accidentally opened. Use a marking pen to write the bread type above each bread piece on the outside of the plastic bag. Repeat this procedure, preparing four or more additional bags. Keep the bags at room temperature for two weeks or until each bread piece has mold. Using a magnifying lens, observe the surface of each bread piece daily by looking through the plastic. Determine when the bread will be considered to have mold such as the first sign of black hyphae. CAUTION: Do not do this project if you are allergic to mold. Even if you are not allergic, leave containers with mold closed so that you do not breathe in an excessive number of spores. Discard the closed containers when the project is finished.

Independent Variable: Types of bread flour

Dependent Variable: Growth of bread mold

Controlled Variables: Type of preservative, testing procedure, containers, temperature, size of bread pieces, environmental conditions

Control: White bread

Other Questions to Explore

1. What effect does temperature have on mold growth?
2. What effect does water have on mold growth?
3. What effect does the type of food have on mold growth?
4. What is pH and how does it affect mold growth?
5. Are there natural ingredients that inhibit mold growth? If so, how effective are they?

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