Lab-8-Food Microbiology

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American Military University *

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202

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Biology

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Dec 6, 2023

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Lab 8: Food Microbiology (100 points) Student Name: Sylvester Dass Student ID: 5671874 Course ID: Bio 202 -Each question on the lab worksheet must be answered completely, thoroughly, in complete sentences and correctly in order to be considered for full credit -If the question asks you to do research or find a source, a reputable, credible and/or scholarly source citation must be included in order to be considered for full credit -If a math formula is required to arrive to an answer, work must be shown otherwise, no credit will be awarded Pre-Lab Questions 1. What is the “danger zone” of bacterial growth that consumers are warned against about holding foods? (5 points) The danger zone refers to the themperature in which bacteria grows the most rapid on food. This range is typically between 40 degrees F (4 C) and 140 degrees F (40 C). 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 list the specific microorganisms, the genus and species, that are used to make each of them. (5 points) Yogurt: Lactobacillus bulgaricus and Streptococcus thermophilus Cheese: various bacteria and molds which depends on the type of cheese as well. Some of the more common ones at Lactococcus lactis and Lactococcus cremoris. Bread: Saccharomyces cerevisiae Food Microbiology
Experiment 1 Results Tables Table 1: Time Required for Methylene Blue Color Change (10 points) Milk Sample Start Time/Date (Step 10) End Time/Date (Step 11) Time Elapsed (End Time-Start Time) 0 hours 10:00 am 24 Nov 2023 9:00 pm 24 Nov 2023 11 hours 1 hour 10:00 am 24 Nov 2023 5:00 pm 24 Nov 2023 7 hours 3 hours 10:00 am 24 Nov 2023 2:30 pm 24 Nov 2023 4.5 hours 4 hours 10:00 am 24 Nov 2023 12:30 pm 24 Nov 2023 2.5 hours Food Microbiology
Experiment 1 Post-Lab Questions 1. Which sample took the least time to become white? Why was that the case? (5 points) The sample that took the longest to become white, was the four hour sample. This is because it spent the longest time in room temperature (danger zone). The growth of bacteria was already at a high state. 2. Which sample took the most time to become white? Why was that the case? (5 points) The sample that took the most time to become white was the 0 hour sample. Because of its limited time in room temperature it didn’t develop nearly enough active bacteria in the beginning. 3. How does refrigeration affect the number of bacteria present in milk? (10 points) Refrigeration is typically done at temperatures under 38 degrees Fahrenheit. This is below the danger zone temperature which creates an unsuitable environment for bacteria to grow. 4. How does pasteurization affect the number of bacteria present in milk? What differences would this assay show if performed using raw (unpasteurized) milk? (10 points) Pasteurization is a kind of sterilization technique. This is when milk is heated and then cooled immediately. Because of the drastic variation in temperature it creates a less than suitable environment that can not be tolerated by bacteria and they die, decreasing the presence of live bacteria in milk. If raw milk were used, it would show a higher bacterial load (both harmful and beneficial) . This would mean that the milk would have probably cause the Methylene blue to turn white faster. 5. What causes the methylene blue to change from the blue color back to the color of white, the usual color of milk in the assay? What is responsible for this change? (10 points) The change from blue to white is because of the amount of active bacteria that is present. As the bacterial populations grow in the milk, they use the oxygen and the methylene blue begins to lose its color. The more there are the faster the color change to white is. Food Microbiology
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