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What Is The Growth Rate of Mold Among Protein, Fat, and Carbohydrate Food Products

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Purpose

To determine which food type will form mold the fastest under different conditions.

Hypothesis

When food loses its freshness, it begins to break down and decay. One of the ways this happens is through the growth of mold on the food. Moldy food is no longer edible and must be discarded. Knowing the average length of time foods remain fresh and when they ought to be replenished can help a household budget and manage its supply of fresh food more efficiently. To this end, it would be helpful to determine the growth rates of molds on certain foods in different environments.

Materials Needed

  • fresh strawberries
  • fresh cucumber
  • cheddar cheese
  • 3 eggs
  • potato
  • bread
  • slice of raw roast beef
  • sour cream
  • 24 sterile plastic petri dishes
  • labels
  • plastic bags
  • refrigerator with a produce storage compartment
  • large shoebox
  • large plastic storage bin
  • gloves
  • surgical mask (to use when observing petri dishes)
  • camera

Experiment

Sterile plastic petri dishes will be filled with various food types representing carbohydrates, proteins, and fats and will be stored in a refrigerated temperature environment, a damp room temperature environment, and a dry room temperature environment. Observations will be made daily on all specimens to determine the rate at which mold forms on each food type in different environments and in all environments in general.

Procedure

  1. Cut the strawberries, cucumber, cheese, potato, bread, and roast beef into pieces. Layer the strawberries into 3 separate petri dishes and do the same with the other cut food items. Separate the egg yolks from the egg whites and lay each egg yolk in a separate petri dish. Scoop out 2 tablespoons of sour cream and layer evenly into 3 petri dishes. When finished, you should have 3 petri dishes of each food item. Be sure to cover each petri dish with its plastic lid and label each one for the food type present in each dish and the location where it will be stored.
  2. Take a petri dish of each food type (group 1) and place each dish in a separate clear plastic bag. Place the plastic-covered dishes carefully into the vegetable storage compartment of a refrigerator, or another part of the refrigerator that can be used for the experiment that will not interfere with other foods in the refrigerator. An empty refrigerator (if available) would be best. Be sure that the temperature in the refrigerator is set to the normal mean temperature that your family uses to keep food cold.
  3. Take the second group of petri dishes of each food type (group 2) and place them each in separate clear plastic bags. Place the plastic-covered dishes carefully in a large shoebox and store them in a dry room at room temperature.
  4. Take the last group of petri dishes of each food type (group 3) and place them each in separate clear plastic bags. Place the plastic-covered bags carefully in a large plastic bin and store them in a damp environment, such as a basement area.
  5. Put on the gloves and observe the petri dishes daily to carefully note how each food type in each environment begins to mold and the order in which each food type in each environment begins to mold. Photograph the mold in each petri dish as soon as it becomes visible and continue to photograph the dishes until all of them fully display mold.

Results

  1. Which group of petri dishes had the most mold overall? What factor in the environment of this group may have accounted for this result?
  2. Which food item formed mold the quickest? Was this food a carbohydrate, protein, or fat? Was this food item also the first to form mold of all the different food types in all three environments?
  3. Which type of foods seemed to form mold the fastest overall—carbohydrate, protein, or fat-concentrated foods? What factors may be responsible for this?
  4. Based on your results, which types of foods should a household plan to replenish more frequently (in order to maintain freshness)?
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