The Effect of Various Pasteurization Temperatures on Bacteria Growth

The experimenter

Researched by Michelle U.
2004-05





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.


RESEARCH REPORT


Nutrients in Milk

Milk is very good for your body. It has a lot of nutrients that are good for your health. Milk was nicknamed “The Nearly Perfect Food” because it is nearly perfect. Some nutrients in milk are water (about 88%), carbohydrates (which provide energy; about 4.9%), fats, proteins (about 3.5%), minerals (about 0.7%), vitamins A, D, F, and K. Another item that is in milk is lactose. Lactose is ONLY in milk. Lactose gives milk its sweet taste. The rich flavor in milk comes from the fat. Milk fat appears in tiny ‘globules’.

Uses for Milk
Milk is used in a lot of other dairy products such as cheese. It’s also used in yogurt, ice cream, butter, cultured buttermilk, cream, evaporated milk, and sour cream. Some kinds of milk are 0%, 1%, 2%, 4%, skim/nonfat, low fat, and whole milk. For an adult you need to drink one glass per day and a child you need three glasses a day.

Kinds of Milk
There are many different kinds of milk. For example, in central Asia they drink camel milk and goat milk. Some kinds of milk are sheep milk (Greece, Iran, Turkey), goat milk (parts of Europe, Latin America, Africa, Asia), camel milk (central Asia, Northern Africa, Arabia) and many others. In America and Canada we drink cow milk. Those are some kinds of milk.

Processing Milk
The steps of processing milk are:
  • Get milk from farmers
  • Separate and standardize the milk
  • Kill the bacteria in the milk by pasteurizing it
  • Bottle and homogenize the milk
That is what each bottle of milk goes through before being put on a store shelf and being bought.

Summary
Milk is very nutritious for human’s bodies. It’s got a lot of nutrients good for our body. It is known as the nearly perfect food because it’s great for your body’s health.

Classification of Bacteria
Bacteria are simple one-celled organisms. Bacteria are the smallest living things known. They measure about 2 tenths to 3 tenths microns (one micron= one milliliter or 1/25,400 inch) in diameter. Most bacteria are microscopic. Scientists classify bacteria “prokaryotes”. Some scientists classify bacteria plants because some kinds can make food from sunlight, as green plants do. Many scientists say bacteria belong to a separate kingdom of living things called “monera kingdom.” There are thousands of kinds of bacteria. Most bacteria are harmless to humans.

Where Bacteria Live
Bacteria live in breathing passages of human’s and animals, soil, hair, air, water, intestines, skin, and your mouth. Bacteria actually live almost everywhere. Not all bacteria are harmful. There are some un-harmful bacteria that protect you from harmful bacteria. The ones that live in your body protect you germs that are harmful, so you don’t get sick. Some bacteria produce vitamins. Bacteria in your body help recycle carbon, nitrogen, sulfur, and other chemicals.

Why Food Spoils
Bacteria grow in some spoiled foods and drinks. That is why eating food that is spoiled is bad for you. The bacterium in it is harmful and can make you sick. Bacteria are used to make alcoholic beverages, cheese, some drugs, and other food. That proves that bacteria are not always bad to your body.

Harmful Bacteria
Sadly, there are harmful bacteria. The ones that are spherical can cause pneumonia, boils, blood poisoning, sore throat, or scarlet fever. Rod shaped bacteria can cause tuberculosis, tetanus, or typhoid fever. The spiral bacterium can cause cholera.

Summary
As you can see bacteria are helpful and harmful. Without bacteria we couldn’t live. Bacteria are very important in our life.
BIBLIOGRAPHY

Brain, Tony, and Parker, David. Young Scientists, Volume 5. Chicago: World Book Inc, 1997. Pp 24-25.

Hutjens, Michael F. “Milk” The World Book Encyclopedia. 2004.

Linda. Personal Interview. December 2004. Spokane Washington.

Marquis, Robert E. “Bacteria” The World Book Encyclopedia. 1995.

Mueller, Michelle "Bacteria: The Good, The Bad, and the Itchy,” Weekly Reader, September 2002: Pg 1-2

Shlessinger, David “Bacteria” World Book Online Reference Center. 2004.



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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