can growth of mold on food be slowed

[thiltz]

I,m doing a science fair project on the growth of mold. I have dipped potato cores in liquids such as alcohol, bleach, apple juice, milk, vinegar, water, etc. I put the cores in small glass jars with wet cotton balls, ten cores in a dark, warm place and ten cores in a lighted area. It has been 2 weeks and the vinegar core in the dark area is the only mold present. The other cores are dark, but I believe it is just discoloration, not mold. Is this possible?

[donnahardy2]

Hi Thiltz,

Two weeks is plenty of time for the mold to grow. You would be able to identify mold growth, because it looks like white fur when it starts to grow. So, if you don't see any white fuzz on your potatoes, you don't have mold growth. Lack of moisture doesn't sound like a problem because you added the wet cotton balls. You have a suitable food source with the potatoes with the apple juice and milk, and the control piece of potato. From your description, it's not obvious what the problem is, but here are a couple of ideas:

1. What temperature did you use? Most molds grow well at room temperature, which is 20 to 22 degrees Centigrade or 68 to 72 degrees Fahrenheit. Heating the environment above 30 degrees Centigrade (86 degrees Fahrenheit) would inhibit mold growth. (Remember when you write up your results to use metric measurements). Do you think the temperature you used was too hot, or could have been hot enough to kill the mold at some point?

2. Mold spores are floating around in the air. Did you leave your samples open to the air, at least for a few hours so some mold spores could drop in?

If your project is due on the 28th, you just have time to set this up again today and see what will happen. However, you should go ahead and write the content of your board with the results of your first experiment, and plan to add the results of the second experiment if it will help the presentation. I have seen some really good project write-ups where the results were unexpected; so don't worry about your lack of results. You can compensate for that with a brilliant explanation of what may have happened. And, if you have discovered something that will keep mold from growing, then your results are very significant.

If you do set up the experiment again today, in addition to the potato, include another food with a higher sugar content, such as oranges, papaya, any real fruit juice or (wet) cat food. You need fast results and these food items will mold quickly. Also, you can compare the fruit results to the potato results.

Now, my most important advice here is to start writing up the various sections of your board today; don't wait until next weekend if your project is due on the 28th. Please let us know if you have any questions.

Good luck!

Donna Hardy

[thiltz]

Donna,

Hi, thank you for the information. I looked at the potato cores today and I still don't see any signs of mold other than the white vinegar core. It's fuzzy, soggy, and has green mold all over it. The other cores look nothing like this. They're a little discolored, which to me looks like they're decomposing. Here's exactly what I did. About two weeks ago, I put wet cotton balls in the bottom of 20 jars. I wrung a lot of the water out of the cotton balls, they were damp, but not soaked. Maybe that was the problem. I dipped each potato core in 9 different liquids and left one undisturbed. I put each core in a jar on top of the wet cotton balls, covered with plastic wrap and poked 6 pin size holes in them. I put 10 of the jars in room temperature ( 70 degrees fahreheit ) exposed to natural sunlight. Then, I put the other 10 jars at the same temperature in a dark cabinent. I watched them everyday and recorded the results, but there wasn't much to record because the results were so slow progressing. It's so aggrevating because I expected to see a lot more mold growth. I don't know what happened. Also, I think the potato cores were a bad idea to use because they brown naturally. In the beginning of this experiment, I thought the browning was mold but as time went on I realized this was not true because the browning really did'nt get any worse. This is the first science fair project that I've done that has been a total mess. I don't know even where to begin because not much has happened. Another strange thing is that the potato core that was left undisturbed has no signs of mold on it. So, not only did I not discover anything that will keep mold from growing, the core that had nothing on it, shows no signs of mold. Strange, I have no idea where to begin. Thanks for your input, I appreciate anything that can help.

[donnahardy2]

Hi Thiltz,

The additional information is very helpful. You have done a reasonable experiment here and you expected mold to grow. You have mold growing on just one sample. You need to analyze your experiment and explain why mold did grow on the one sample, but didn't grow on the rest of the samples.

Here's where to begin. Go though step-by-step and analyze your experimental set-up and try to identify the most cause of no mold growth.

1. Potatoes are a good growth medium for mold. The potato blight in Ireland in the mid 1800's was caused by a mold; the medium microbiologists use to grow cultures of fungi is called potato dextrose agar and is made from potatoes. Potatoes have a slightly acidic pH and low nitrogen content, and this is definitely compatible with growing mold. Here is a site that includes the composition of potatoes:
http://www.fineli.fi/food.php?foodid=162&lang=en
(I would recommend including historical and composition information in your background section to support your use of potato as a sample.)

The only thing I can think of that would be a problem (for growing mold) is the presence of an inhibitor in the potatoes you used. Where did you get your potatoes? You should track the source of the potatoes, contact the distributor or grower, and find out if anything was added to the potatoes that would inhibit mold growth. I know that fungicides are added to papayas, but I don't know about potatoes. Maybe you can find out. If something was added, get the exact chemical name of the product.

2. Temperatures: The temperature of 70 degrees F (21 degrees Centigrade-remember to use metric for your Science Fair board) is ideal for mold growth. I can't think of anything about this temperature that would inhibit mold growth.

3. Moisture. Fungi require moisture for growth. Excess water is not required, but a relative humidity of at least 50% is required. You say you removed most of the water from the cotton balls, so maybe there wasn't enough moisture to support mold growth in the jars. And you said you put pinholes in the lids, so if the relative humidity was lower than 50%, moisture in the jars may have evaporated. What was the weather like when you did your experiment? If it was rainy during the two-week experiment, then lack of moisture was probably not the problem. If it was dry, however, maybe this could be the reason. Why don't you research the local weather reports for the time of your experiment and determine if the relative humidity was less than 50%. This might explain your results. If this were a possibility, then I would recommend including a plot of time (x-axis) vs. relative humidity (y-axis) to support your theory.

4. Why did mold grow on one sample? You do apparently have mold growth on growth on one sample, and no mold growth on the control. What was the difference between the two samples? One difference was pH, because vinegar would lower the pH of the sample. Do you have any way to test the pH of your potato samples? If you can get some pH paper or access to a pH meter, you can measure the pH of the potatoes you used. Science fair judges love seeing measurements, so please do this if you can. You should measure the pH of a potato core and a potato core dipped in vinegar. Potato dextrose agar is pH 5.5 and ideal for most fungi. Which of your samples (potato, or vinegar-dipped potato) is closer to pH 5.5?

The other possibility is a difference in moisture. Do you think it is possible that you added a couple of drops of vinegar to the sample that molded? Did it look any wetter than the other samples? If this sample did look wetter than the others, the the reason for the difference in results is due to moisture differences.

5. Presence of mold spores. One thing about the sample that did grow mold is that it confirms that mold spores were present in the environment. With mold projects, you always assume that mold spores are present in the air and that the spores will land on a suitable food source, germinate, and start growing. So the failure of the other samples to support mold growth was not due to an absence of mold spores. Mold spores were definitely around, but something about the environment in the other jars kept them from growing. (I recommend including a paragraph about fungal spores, where they are found, and how they start growing in your background section).

The browning reaction you observed is a natural enzymatic reaction due to exposure of the potato to air (and a possible topic for another science fair project), and although it made your samples look less attractive, it did not affect the growth of the mold. So please don't worry about this.

So, you don't have time to worry about the lack of results. You actually do have results; you just have no mold growth. You have lots of work to do to investigate and explain what happened in your project.

Do you have any other questions?

Donna Hardy

[thiltz]

Donna,

Thank you so much for the information, it was very helpful. I'm going to get busy writing my results and conclusion. Thanks again!

[thiltz]

Donna,

I have one more question. One of the potato cores I tested, I rubbed it on a piece of dirty, worn clothing that was in my dirty clothes pile before placing it in the jar. That core looked the best out of all of the cores. Could this be because of the salt from the body or do you have any explanation why this core looks the best? Also, before throwing away my test jars, I took the cores out of the jars and examined them more closely. I did find traces of mold on almost all of them after viewing them close up. I'm so glad I did this, but my respitory system was'nt to happy. The bleach core had orange spots on it. Which after doing some research, I found out that this was a form of mold. I'm sorry to trouble you again, but I can't find anything on this and the only explanation I can come up with is relating to the salt or perspiration on the body. Thanks again for all the helpful information.

[carolinethorn]

Hi,

Skin naturally has lots of bacteria and fungi on it. Can you come up with another reason now to help explain the growth on the potato that was rubbed on the clothes?

-Caroline

[donnahardy2]

Hi Thiltz,

Caroline has given you a really good hint about your results. When you exposed the potato cores to your fingers and clothing, you were transferring other organisms onto the potatoes. It sounds like what you grew was a mixed culture of microorganisms, not just mold. Were the orange spots furry? Molds always start out as white fuzz and then develop colored spores later. If not, then this could have been yeast. Yeasts can come in pink, orange, and other colors and usually are a little shiny in appearance. Or it could have been a bacterium. Lots of microorganisms have pigments that protect them from ultraviolet light, kind of like a built-in sunscreen. The microorganisms that you grew would be classified as mesophilic aerobes (liking medium temperatures and able to grow in the presence of oxygen). You could do your experiment at a lower or higher temperature and with or without oxygen present and grow completely different types of microorganisms, but you can save that for next year's project.

Microorganisms have the role of recycling carbon, nitrogen, and other elements so other organisms can reuse them. It sounds like your microbes were doing their job and producing aromatic breakdown products. You should always avoid breathing in when examining mold cultures that have developed spores.

Did you see any difference in the type of microbes growing on the different samples? I think it was great that you spent some more time and carefully observed the results of your samples.

Donna Hardy