Bacterial fungi lab

Published on March 9, 2010

Purpose: To demonstrate how fast food decays and supports bacterial and fungal growth. (Which is more prevalent, bacteria or fungi?)

Method: Bacterial fungi lab was set up on March 4th, 2010 at 9:30pm.
Four individual plastic containers received two (1-2 inch) slices of bread, apple, chicken, or potato. One teaspoon of water was added to each (by able lab assistant). Each container was closed, and then sealed with plastic masking tape. It was very fun to do!

Initial lab set up date: March 4th, 2010
Two week observation date: March 18th, 2010
Three week observation date: March 25th, 2010
Four week observation date: April 2nd, 2010
Five week observation date: Appril 9th, 2010

Apple container observations
2 weeks: Yellow and brownish coloring, some darkened areas, some black areas.
On side of apple, what appears to be whitish, greenish growth.
No odor
3 weeks: More brown than yellow, has almost turned to mush. There is a lot of liquid in the container.
Slight odor
4 weeks: Mostly black with brown portions. Package seems to have exploded but most of the contents remain in the container. I don’t know how it got out. All of the containers are now in a holding plastic bag due to the smell. I am glad I did this as the apple seems to have covered the bag! Slight odor.
5 weeks: All black, mostly liquid. Slight odor.

Potato container observations
2 weeks: Potato has turned almost completely brown, very thin white hairish growth on surface of apple. Some blackened areas.
No odor
3 weeks: Has turned almost all black. Some moldy patches, but not much change from two weeks.
No odor
4 weeks: Mostly black and white. Appears rather hairy in areas. No odor.
5 weeks: All black, more fungus than before. Seems stuck to bottom of container. Slight odor.

Chicken container observations
2 weeks: Yellowish film covers surface, although no moldy appearance such as with bread, potato and apple. Very strong odor (have to keep all the samples in the other room because of the stink of the chicken sample)
3 weeks: Appearance is almost the same as at two weeks. Some white growths present, and more liquid than before. No real color change is observable.
It has a terrible odor. I had to place it in an area where it was closed off from living area because the smell is intoxicating (even though it is sealed!).
4 weeks: Surprised to see that it has not changed so much except that it is rather milky in appearance, guessing that bacteria is beginning to transform it? Also, seems to have expanded.
It now stinks very strongly. I have had to hide the experiment deeper in my house as the stink seems to seep out easily.
5 weeks: Almost unrecognizable, very white, watery, extremely strong odor. Quite a lot of the contents has exploded out. I am glad it was in another protective bag.

Bread container observations
2 weeks: Green, white and yellowish growth over surface, seems to have expanded within container.
3 weeks: The bread is almost unrecognizable, and has expanded almost to the entire container. It’s colors are orange, yellow and brown, and some green.
No odor.
4 weeks: The bread no longer had a bread shape. It has expanded fully and sticks to the side of the container. It is mostly brown, and green.
Slight odor.
5 weeks: There is no sign of bread left, just big globs of and brown. Slight odor.

2 weeks: About a week ago, I came home and noticed that there was a strange smell in the apartment, but could not recognize it. I threw out all of the garbage, and checked the apartment for the cause, but could not imagine where it had come from. Sitting down to review my biology assignments, I realized what it must be! Even after only a week, the chicken had started to smell so bad. For the other samples, however, there was no change that I could see. I am not sure of the outcome of this experiment. Also, while I think I can recognize fungal growth, I don’t think I can “see” bacterial growth. It will be interesting to watch what happens in the coming weeks.
3 weeks: I have been looking at the containers trying to guess whether fungi or bacteria are growing. If I were to guess, I would say that the chicken does not have and fungi on it. The apple also does not have any fungi. However, the bread and potato seem to have fungi on them
4 weeks: As written above, the samples have really started to change drastically as the breaking down process continues. The chicken is very scary to approach, as the smell is quite intoxicating. I wonder how long it will take for them to disappear? I also wonder how any air got into the containers?
5 weeks:
It seems that the change in the samples has reached its climax, and I have tried to imagine what will happen next. If they are exposed to air, I am guessing that they will start to disappear? The chicken is definitely the most interesting, and being made of similar material, makes me wonder what happens to dead humans who are found after some time.

1. Explainin the decay progression from setup to Week 5.
The decay process took place largely because of the presence of water. Although natural components of the food would slowly break down the food in natural air, the addition of water made the process happen much faster.

2. Which is prevalent, bacteria or fungi?
Fungi was more prevalent than bacteria. It grew on the potato, the bread and the apple. Speaking as a layman, I am surprised that anything could get in there to break it down. I thought the containers were completely airtight, except for what was in there at the time of sealing. The chicken was amazing. I am guessing that the natural living processes of the chicken were broken down by the water, and the air over time, causing such a terrible smell. I am interested to learn the actual process in which this happened.

3. Which food substrate decayed more quickly?
The quickest decay was seen in the bread, after only a few days. The slowest was the potato.

4. How would food preservatives slow the decay process? Why?
I don’t think I have ever taken the time to think about food preservatives. I have heard that they may not be good for you, but never taken the time to investigate their properties. According to Wikipedia, food preservatives or additives aim to stop the growth of bacteria and fungus by blocking their natural breakdown process. One of these additives is antioxidants (oxygen absorbers). Antimicrobial agents inhibit the growth of bacteria. It is interesting to learn that the US does not require fruit producers to label the preservatives on their produce.

All foods contain in them natural substances which cause their slow decay over time (acids, enzymes, alcohols). Food preservatives aim to make food stay attractive, and maintain their natural taste and shelf life.

One of the first natural preservatives, which are still used today are salt and sugar. Salt uses the process of osmosis to deny bacteria an essential component to the breaking down process. Salt also stops yeasts and molds. Well salted meat can last for years.

Sugar is another natural preservative. It also uses the process of osmosis to draw water out of bacteria to help to stop the growth of microorganisms.

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