Bacteria and Thawing Methods

Complexity level:	7
Project cost ($):	30
Time required:	2 day for preparation, 5 days for science fair project
Material availability:	Access to laboratory equipment (eg. petri dishes)
Safety concerns:	Always follow laboratory safety guidelines and always practice sterile technique when handling microbes. Never have any food or drink at your workstation and always thoroughly wash your hands with disinfectant soap or alcohol before leaving your workstation. Always dispose of used material in a biohazard bag. If none are available, the bacteria should be destroyed with bleach before being disposed of.

Hypothesis

Meat that is thawed in the microwave oven showed the least bacteria contamination.

Overview

Bacteria in the meat

Although most bacteria are harmless to humans, some of them are disease-causing. Pathogens are bacteria that can cause illnesses. Food-borne illnesses occur when pathogens enter our food. Bacteria can be found in any kind of food but they have a tendency to flourish in of protein rich foods like meat, poultry, eggs and dairy products.. The food that we purchase is commonly already contaminated by bacteria, but this problem is easily solved by properly cooking our food.

Meat can be kept in the freezer for long periods of time without getting contaminated. It needs to be thawed before cooking. The most common method of thawing is to leave the meat at room temperature for a few hours . However, the longer the meat is left outside the freezer for thawing, the more bacteria contamination it experiences. Other methods of thawing are by leaving the meat in the refrigerator or by using a microwave.

Scientific Terms

Bacteria, pathogens, food-borne diseases, contamination, microorganism

Materials

The materials required for this science fair project are:

-    3 agar Petri dishes
-    3 disinfected swabs
-    1 bottle of disinfected water
-    1 sterilized chopping board
-    1 sterilized knifes
-    1 refrigerator with freezer
-    1 microwave oven
-    1 piece of irradiated chicken part bought from the cold storage supermarket
-    3 beakers
-    1 Marker pen

Procedure

1.    The independent variable for this science fair project is the method of defrosting the chicken meat – at room temperature, in a refrigerator and using the microwave. The dependent variable is the size of the bacteria growth in the Petri dish. This is determined by measuring the size of the bacteria growth using a ruler. The constants (control variables) are room temperature, the amount of sunlight and the ingredients in the Petri dish agar.

2.    Prepare 3 Petri dishes are prepared using agar and store themin a refrigerator. The Petri dishes are brought to room temperature before the start of experiment by taking them out of the refrigeratorLabel the Petri dishes as “Room temperature”, “Fridge” and “Microwave”.

3.    Using a knife and a chopping board, cut out 3 equal cubes of irradiated chicken meat   Keep the chicken cubes inside the freezer for a day.

4.    The next day, the 3 pieces of frozen chicken cubes are removed from the freezer. Remove the 3 cubes of frozen chicken from the freezer the next day. Keep the 1st cube of chicken in the fridge for the next 12 hours to thaw . Leave The 2nd piece of chicken at the kitchen counter for the next 4 hours to thaw at room temperature. Use the microwave to thaw the 3rd piece of chicken

5.    Label the 3 beakers as “Room Temperature ”, “Fridge” and “Microwave”. Pour 100 ml of disinfected water into each beaker and soak the thawed meat in it, according to the labels on the beaker for ten minutes.

Wash the swab with sterilized water and dip it into the beaker. Swipe the swab at the center of the agar surface according to the label on the beaker and Petri dish

6.    . Cover the Petri dishes and keep them in a cool, shaded place for the bacteria to grow, for the next 5 days.

7.    Measure the diameter of the bacteria colony growth after 5 days and recordit in the table provided below.

food science fair project

Results

The results show that the meat thawed using the microwave had the least amount of bacteria contamination followed by the meat thawed in the fridge. The meat thawed at room temperature had the most bacteria contamination

Thawing method	Outside	Fridge	Microwave
Bacteria growth (mm)	53	22	17

The graph below represents the results of our science experiment:

raw meat science fair project

Conclusion

The hypothesis that the meat thawed in the microwave oven experiences the least bacteria contamination is proven to be true.

Bacteria will contaminate meat very quickly. Leaving meat to thaw at room temperature for too long can cause the food to be unsuitable for consumption. Thawed meat should always be cooked immediately. .

Also consider

The science fair project can be repeated by varying the types of food.

The experiment can also be repeated by using other thawing methods (eg. thawing the meat in a container filled with water, or in a disinfected plastic bag). .

References

The truth about irradiated meat - http://www.mindfully.org/Food/2003/Irradiated-Meat-TruthAug03.htm

Bacteria that cause food borne illness - http://www.infoplease.com/ipa/A0762206.html

What is the best way to thaw frozen meat? - http://www.wisegeek.com/what-is-the-best-way-to-thaw-frozen-meat.htm

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