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The Effect of Various Pasteurization
Temperatures on Bacteria Growth |
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Researched by Michelle U.
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PURPOSE
The purpose of this experiment was to compare the spoilage rate of non-pasteurized, pasteurized, and ultra-pasteurized milk at two different temperatures.
I became interested in this idea when I read an article about milk and then talked to an Inland Northwest Dairies employee about how they keep milk from spoiling.
The information gained from this experiment could help society by showing parents, restaurant owners, food service managers in schools or hospitals, and consumers what kind of milk will last for the longest time at various temperatures.
HYPOTHESIS
My first hypothesis was that ultra-pasteurized milk would last longer than pasteurized at room temperature.
My second hypothesis was that pasteurized milk would last longer than non-pasteurized milk at room temperature.
My third hypothesis was that milk of all types would spoil more quickly at warmer temperatures.
I based my hypothesis on a statement by an Inland Northwest Dairies employee, Ron Underwood. “The higher the temperature the milk is pasteurized at, the longer it will last.”
EXPERIMENT DESIGN
The constants in this study were:
- The amount of milk tested.
- The containers the milk is kept in.
- The temperature the milk is kept in.
- The percent of fat in milk.
- The brand of milk tested.
- Where the milk is tested.
- How the milk is tested for spoilage.
- Types of vials the milk is tested in.
The manipulated variable was the kind of milk tested.
The responding variable was the amount of bacteria in the milk.
To measure the responding variable I will count the bacteria.
MATERIALS
| QUANTITY | ITEM DESCRIPTION |
| 4 pints | Non-pasteurized milk |
| 10 pints | Pasteurized milk |
| 10 pints | Ultra-pasteurized milk |
| 1 |
1 ml. pipette |
| 25 |
Pipes for pipette |
| 1 |
Colony counter (Magnifier
for counting colonies) |
| 24 |
Petri Dishes |
| 1 |
Jar of agar |
PROCEDURES
1. Get non-pasteurized milk.
2. Get pasteurized milk
3. Get ultra-pasteurized milk.
4. Sterilize the pasteurized milk using sterilized water.
5. Put one milliliter of non-pasteurized milk into the plate with one-milliliter pipette. Throw away the disposable plastic pipe.
6. Put one milliliter of pasteurized milk that has been kept in a refrigerator in the plate with your one-milliliter pipette. Throw away the disposable plastic pipe.
7. Put one milliliter of ultra-pasteurized milk that has been refrigerated in the plate with one-milliliter pipette. Throw away the disposable plastic pipe.
8. Pour in the agar (just enough so that the bottom is completely covered).
9. Mix the milk by gently swirling the plate slowly (with the lid closed) and let the milk and the agar mix.
10. Place in an incubator at thirty-two degrees Fahrenheit.
11. Put one milliliter of non-pasteurized milk that has been kept at 60 degrees Fahrenheit using your 1-milliliter pipette. Throw away your disposable plastic pipe.
12. Put one milliliter of pasteurized milk that has been kept at 60 degrees Fahrenheit using your 1-milliliter pipette. Throw away your disposable plastic pipe.
13. Put one milliliters of ultra-pasteurized milk that has been kept at 60 degrees Fahrenheit using your 1-milliliter pipette. Throw away your disposable plastic pipe.
14. Repeat steps 8-10.
15. Do steps 4-10 using one-tenth milliliter pipettes and 4,11-14 using one tenth.
16. Repeat steps one through 15 three times again.
RESULTS
The original purpose of this experiment was to compare the spoilage rate of non-pasteurized, pasteurized, and ultra-pasteurized milk at two different temperatures.
The results of the experiment were that all types of milk grew more bacteria colonies in warmer temperature, except the ultra-pasteurized milk, which grew no colonies at all.
See the table and graph below.
CONCLUSION
My first hypothesis was that ultra-pasteurized milk would last longer than pasteurized at room temperature. My second hypothesis was that pasteurized milk would last longer than non-pasteurized milk at room temperature. My third hypothesis was that milk of all types would spoil more quickly at warmer temperatures.
The results indicate that my first hypothesis should be accepted because the ultra-pasteurized milk had less bacteria colonies than the pasteurized. My second hypothesis should be accepted because the pasteurized had less colonies than non-pasteurized milk. My third hypothesis should be accepted because all types of milk grew more colonies at room temperature.
Because of the results of this experiment, I wonder how long it would take for the ultra-pasteurized milk to grow colonies, since it grew none in a week at either temperature.
If I were to conduct this project again I would do longer trials, conduct more trials, and do more research about why bacteria makes food spoil or why it grows. I would also find out what kind of bacteria grew.
ACKNOWLEDGEMENTS
- I would like to thank the following people for helping make my project possible:
- My mom for helping me and supporting me with my project.
- My dad for helping me and supporting me, driving me to Spokane, and taking me to Tree Top every Tuesdays and sometimes Thursdays, and for getting the milk samples.
- Mr. Newkirk for making my project as good as it could get, and also for pushing me to try as hard as I could.
- Mrs. Helms for helping me with what I didn’t know or understand.
- My sister, Rachel, for giving me ideas for picking my project and then for helping me find books and suggesting some for studying.
- My mentor, Jeanette Green, for helping me with my project.
- Linda for letting me interview her in Spokane.
- Janyn for helping me with my display board.
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