Top Banner
The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class. I encourage you to have some great discussion with you students about the results. I love drawing conclusions from results; it is the thinking part of the investigation. Please don’t be offended by my notes. As scientists, we need to be critical of the experimental procedure and the results obtained. We are the checks and balances of the scientific method. Without our ability to think and reason, the experiment/data mean very little. Remember, the interpretation of results may lead to modification of the experiment, not necessarily answers!!
15

The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Dec 14, 2015

Download

Documents

Ross Watson
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

The Effect of Cooking Temperature on the Amount of Bacteria in Ground

Beef(8/13/2009)

The results are exactly what you can expect to happen in class. I encourage you to have some great discussion with you students about the results.

I love drawing conclusions from results; it is the thinking part of the investigation. Please don’t be offended by my notes. As scientists, we need to be

critical of the experimental procedure and the results obtained. We are the checks and balances of the scientific method. Without our ability to think and

reason, the experiment/data mean very little.Remember, the interpretation of results may lead to modification of the

experiment, not necessarily answers!!

Page 2: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.
Page 3: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

What happened here?Teachable moment!

I love it when this happens!!!!!!

Page 4: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Notice the lack of uniformity in the plating process. This results in differing number of colonies due to procedure, not bacteria present.

Page 5: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Nice results!!!!!However, notice the writing

covers some results.Again, the plating/swabbing is

not uniform on all plates.

Page 6: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

These guys had a great time!Observations were recorded directly on the plates…probably would be better to

record in lab journal.

Page 7: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Explain the lack of difference between 120 and 140 o F…we

need more trials don’t we.

Page 8: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Quantifying Data: Counting Colonies

• From the back/bottom of the sealed plate, count each colony (spec) of bacteria

• As you count mark the colony with permanent marker

• I count the first 100 colonies, then I let my partner count the next 100. We trade off until all colonies are counted.

Page 9: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

The black dots are the colonies I counted. Using the marker is essential to keep track of counted colonies.

Note: It is important to remind students that not all of these bacteria here are pathogenic. If you purchase meat at your local supermarket, the facility where the meat was processed and the supermarket are inspected for pathogens and/or bad practices. Sometimes the meat even goes through an irradiation process to kill the bacteria. However, we all know that finding E coli 0:157 is like finding a needle in a haystack. It could be in your burger.

Page 10: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

1 bacterium after 24 hours of incubation at 37oC = 1 colony of bacteria

Results: 0 colonies (interpretation: no bacteria on TSA plate)

Page 11: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Results: 500 colonies (interpretation: WOW, there’s a lot of bacteria in ground beef. I hope none of them are pathogenic!) note: you’re right, I didn’t really count them ;-)

Page 12: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Results: 400 colonies (interpretation: 120oF is not very effective at killing bacteria) (Practical application: If any of these bacteria are pathogenic, I am at risk of ingesting a food-born pathogen when I eat this rare burger.)

Page 13: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Results: 70 colonies (interpretation: 140oF is relatively more effective at killing bacteria when compared to 120oF.) (Practical application: Nick Adams, colleague here at West, says he would eat this burger. There is still the potential for food-born illness if the bacteria are pathogenic…Salmonella or E coli 0:157.

Page 14: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

160oF

Results: 0 colonies (interpretation: ????)(Practical application: ????)

Page 15: The Effect of Cooking Temperature on the Amount of Bacteria in Ground Beef (8/13/2009) The results are exactly what you can expect to happen in class.

Have a great year of discovery, intrigue and enlightenment

through scientific investigation.