Lab-8-Food Microbiology

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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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Experiment 2 Results Table Table 2: Yogurt pH Results (10 points) Sample (Step #) pH 2 6-7 6 8 10 7 14 4-5 15 4 Food Microbiology

Experiment 2 Post-Lab Questions 1. Make a graph of the pH changes over the course of the experiment (from Table 2) and insert it here. Explain what causes the pH to change at each step? Why does the pH change at each of the steps? (15 Points) Step 2 Step 6 Step10 Step 14 Step 15 0 1 2 3 4 5 6 7 8 9 pH Levels of Each Step Column2 Experiment Steps pH Level The milk was initially measured at a pH roughly between 6 and 7 in the beginning. After the first session of being heated It rose the pH slightly to 8 because of the pasteurization process bacteria is destroyed , After the addition of yogurt, the microbes we reintroduced and slowly fermentation began causing the ph to drop towards normal. During the incubation process microbes underwent a huge growth phase converting lactose into lactic acid. This causes the ph level to significantly drop. 2. In the protocol you used to make yogurt from milk, why was it necessary to raise the temperature of milk to 85 degrees for two full minutes? (5 points) Heating the temperature to 85 degrees for 2 full minutes is important for multiple reasons: Pathogen elimination: Harmful microorganisms including pathogenic bacteria are eliminated this way. Denaturation of proteins: High temperatures also cause denaturation of proteins in milk including the unfolding of proteins. This contributes to the geletain like structure of yogurt. Creates an optimum environment for yogurt cultures Food Microbiology

3. How does the consistency of the milk change during the production of yogurt? What facilitates this change in the pH? Is this related to the breakdown products of lactose and what about the taste? (10 points) As the bacteria consumes lactose, lactic acid is produced which drops the pH creating a more acidic mixture. Denaturation of proteins occur and casein protein in milk coagulates and thickens the milk to the yogurt gel like texture. References Food Microbiology

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