Question

Experiment #13 -         Mold Growth on Bread and Fruit

What are Optimal Conditions for Fungal Growth?

Purpose

To describe the growth requirements of fungi.

To determine the optimal conditions for fungal growth

To determine the effects of pH on fungal growth

Materials

2 tsp. Lemon juice         

1/2 C. Sugar                      

2 tsp. White vinegar     

Plastic bags                       

Measuring spoon           

2 - 250 mL Beaker         

Permanent marker

*3 Slices of bread

*Apple

*Sharp utensil to cut apples and bread

*Sauce pan

*Stove or microwave oven

*Water

Procedure

Add 120 mL of water to a saucepan or large microwaveable bowl and mix in 1/2 cup of sugar.

Gently heat the water/sugar mixture on the stove or in the microwave, stirring occasionally until all of the sugar is dissolved. Use caution when removing the solution from the microwave/stove as it will be hot. Allow the solution to cool.

Label the plastic bags with these titles: “bright, control”, “bright, water”, “bright, sugar”, “bright, lemon”, “bright, vinegar”, “dark, control”, “dark, water”, “dark, sugar”, “dark, lemon”, and “dark, vinegar”.

Cut the three slices of bread into 12 total pieces (4 pieces from each slice).

Cut the apple into 10 slices. Cut slices of the same thickness approximately the same size as the ¼ piece of bread.

Place one piece of bread and one slice of apple into a plastic bag. Repeat this process until you have 10 bags, each with one piece of bread and one slice of apple.

Measure a small amount of water into a 250 ml beaker

Add 1 tsp. plain water to the bags labeled as water; add 1 tsp. of the sugar-water solution (prepared in Step 1) to the bags labeled sugar; add 1 tsp. of lemon juice to the bags labeled lemon; add 1 teaspoon white vinegar to the bags labeled vinegar. Do not add anything to the bags labeled control.

Find a well-lit, warm location in which to place the bags labeled bright (for example a windowsill or under a lamp).

Find a dark, warm location in which to place the bags labeled dark (for example a warm closet).

Examine the bags every 1 - 2 days for 2 weeks and look for mold formation on the bread and apple pieces. Take particular note to which environmental condition(s) mold formed in first and last. Also, make sure to note which environmental condition(s) grew the most and least mold. Use the following scale to assess the extent of mold growth

0 = none

1 = little/some (1-25%)

2 = moderate (26-50%)

3 = heavy (51-75%)

4 = extensive (76-100%)

Record your results in Table 1.

Do not open the bags when you are finished with the experiment. This will disperse mold spores and contaminate your work/living area. Dispose of the sealed bags in the trash and remove the trash bag.

Table 1 – Growth Results
Condition	Extent of Growth		Pigmentation of mold
	Week 1	Week 2
Bright, Control
Bright, Water
Bright, Sugar
Bright, Lemon
Bright, Vinegar
Dark, Control
Dark, Water
Dark, Sugar
Dark, Lemon
Dark, Vinegar

Questions

Which condition produced the most mold growth? The fastest? The least? The slowest?

Based on your results, what conditions are most favorable for mold growth on bread and apples?

How would changing the type of bread (fresh from a bakery, no preservatives versus prepackaged with preservatives) affect the results?

How would changing the temperature at which the bags were incubated affect the results?

How would you test this hypothesis?

Look up the pH of lemon juice and vinegar. Based on your results and your knowledge of favorable environmental conditions for fungal growth, what can you conclude about the effect of pH on growth? How would making the pH more basic affect growth?

Answer 1

Table 1 – Growth Results
Condition	Extent of Growth		Pigmentation of mold
	Week 1	Week 2
Bright, Control	None	None	none
Bright, Water	None	None	none
Bright, Sugar	Moderate	Heavy	white
Bright, Lemon	moderate	heavy	Green
Bright, Vinegar	None	None	None
Dark, Control	None	None	None
Dark, Water	None	Moderate	White
Dark, Sugar	Moderate	Heavy	Green
Dark, Lemon	Heavy	Extensive	Dark green/black
Dark, Vinegar	None	None	none

1. The most mold growth will be obtained in lemon and sugar because acidic condition enhance the fungal growth.

          The fastest growth will be in lemon dark and the least will be in vinegar in each bag.

          Vinegar is antifungal, it will not allow the growth of fungus.

2. The dark conditions with slightly acidic nature and sugar is favorable.

3. A bread with preservative will be protected against fungus for some more days as compared to the fresh b read.

4. The higher and lower temperature will decrease the growth of fungus while a moderate temperature of 20 to 25 degree celcius is favorable.

5

We will incubate the fungus with all the necessary ingredients at different temperatures and observe the growth.

6. The pH of both vinegar and lemon is around 2.0, it helps in enhancing the growth of fungus. but vinegar is antifungal. A pH towards basic pH will decrease the growth of the fungus.