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Lab 6 Food Microbiology BIO250L”

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“Pre-Lab Questions”

1. Escherichia coli is one of the most common causes of foodborne illness, yet it is also a common microorganism found within the human gut. What explains this disparity?
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2. There are several foods and beverages listed in this lab that are created through the actions of microorganisms. Name five of the foods and the specific microorganisms that are used to make each of them.
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3. Using an online research tool such as the A-Z index on the CDC website, explain why Listeria monocytogenes is a major threat to pregnant women and their developing fetuses, who are ten times more likely to get sick than other demographic groups.
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“EXPERIMENT 1: Assessing the Bacterial Load of Milk with Methylene Blue

Results Tables

Table 1: Time Required for Methylene Blue Color Change

Milk Sample

Start Time/Date (Step 10)

End Time/Date (Step 11)

Time Elapsed

(End Time-Start Time)

0 hours

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1 hour

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3 hours

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4 hours

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Post-Lab Questions

1. On average, which sample took the least time to become white? Why do you think this was the case?
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2. On average, which sample took the most time to become white? Why do you think this was the case?
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3. How does refrigeration affect the number of bacteria present in milk?
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4. How does pasteurization affect the number of bacteria present in milk?
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5. What differences, if any, would this assay show if performed using raw (unpasteurized) milk?
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6. What differences, if any, would this assay show if performed using milk that was past its expiration date and had an off-putting odor?
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“EXPERIMENT 2: Yogurt Preparation

Data Tables

Table 2: Yogurt pH Results

Sample (Step #)

pH

2

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6

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10

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14

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15

Post-Lab Questions

1. Make a graph of the pH changes over the course of the experiment. Insert it below. How does the pH change at each step? Why?

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2. What attributes does lactic acid confer to yogurt?
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3. How does the consistency of the milk change during the production of yogurt? What facilitates this change?
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4. What are the breakdown products of lactose?
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Insert a photo of your pH strips. Include your name and access code handwritten in the background of your photo.