Yogurt culture experiments can be done with safe household items. Although items
ID: 99499 • Letter: Y
Question
Yogurt culture experiments can be done with safe household items. Although items are generally regarded as safe, it is important to properly sanitize or disinfect equipment and surfaces after the experiment. Do not allow children or others to come into contact with aspects of the experiment, and never ingest any product of the experiment. Contact the instructor if there is a safety concern or any other reason an alternative lab is needed. This experiment is to culture yogurt from a commercial starter culture and observe changes in the milk medium. The protocol will mostly follow lab exercise 7-8. Variations can come from brand of starter yogurt used, milk type and quantity, temperatures used and method of measuring, containers, and option to take pH measurement. You may follow the lab book or example protocol. There are several examples on the internet if you need more examples, and you are required to have a minimum of two references in your report. You will need to take pictures of the observations and methods, and taking notes may be useful for writing the report. The grade of this lab is NOT dependent on expected results. However, it is affected by rationalizing methods, observations, and discussing your results.
II. INSTRUCTIONS 1) Read the lab book exercise 7-8, example outline, research the internet, and plan out your experiment. At a minimum, you will need yogurt with active cultures, milk, bowl, stirring utensil, and a heating source. Typically you would use a pot, stovetop, whisk, thermometer (of any kind, as long as there are no safety concerns), plastic wrap, measuring cup, and a clear plastic bag. Some students choose to measure pH (you could alternatively research the beginning and ending expected pH measurements for the report).
2)Plan out your methods. Decide the amounts, temperatures, and time periods you will use. You can follow one protocol or combine aspects, but remember to cite your sources and use detailed descriptions. For example, a student who does not have a measuring cup may use a standard size coffee mug to measure milk. A student who does not have a thermometer may combine a specific amount of hot tap water (usually around 65°C/149°F) with part cold tap water to estimate a temperature. Alternatives do not affect your grade, but lack of detail will
. 3) Execute your experiment. Do not forget to make observations at the start. If you plan to observe thickness in a plastic bag at the end, do the same at the beginning (and same thing if you plan to let it fall off a spoon or fork). If you do not see results, this is not a problem. However, the results, interpretation, and alternatives must be discussed in your report
. 4) Finish and write report. When your last observations are made, materials can be discarded and other items can be cleaned. Properly disinfect any working surfaces, and wash/sanitize any containers and utensils. A small amount of bleach is recommended, but not needed if you have other preferred methods. Do not ingest your experiment as part of this class.
III. SPECIFIC LAB REPORT & SUBMISSION INSTRUCTIONS General lab report instructions for a manuscript format are below in another section. If you are not familiar with this standard format, read those instructions first. These contain the second and third most common mistakes, which are not citing sources and not using paragraph format like listing items or using bullet points. Details remain important in this experiment, specifically on observations, and the interpretations by association. Having expected results is not a grading criterion for this activity, but discussing any problems or other alternatives is. Specific to this report, you must include at least two references. Below are other considerations specific to this report: Introduction-
1) What was the purpose of this experiment (i.e. what objective do you accomplish)? What bacteria are you trying to culture? What classification are these bacteria?
2) What conditions are optimal for this growth (temperature, pH, etc.)? What are potential variables you can change in the culture?
3) Briefly preview (summarize) what was done in the experiment and the end results.
Materials & Methods-
1) What materials did you use (sentences, no listing!)? What brands (as applicable)? Was there any preparation, such as letting the commercial yogurt incubate at room temperature?
2) Describe your methods as you did them. Do not personalize (I, my, we) and cover beginning to end (preparation, execution, and analysis of results). Specifically mention the observation method of beginning yogurt, mixture, temperature, pH, and incubation periods
- 1) Describe observations at the beginning of the experiment. What color, thickness, homogeneity, bubbles did you observe?
2) Describe all the changes in from the beginning of the experiment to the end. What were the temperatures? What was the pH or expected pH? Was there any color change in the solution? Was there a change in thickness or bubbles?
3) Focus only on observations, conclusions and interpretations belong in the next section. Discussion-
1) What conclusions can you make from your observations? Can this be interpreted as growth or no growth?
2) How did your results lead to your conclusion? Did you deviate or change something that helped or hurt the culture?
3) Was there anything unexpected in the results? Were there other parameters that could have been measured or measured better (e.g. pH strips or a thermometer)? Could your protocol be modified for an anticipated better result? References (Bibliography)
1) Reference each source you used in APA format. Then cite the references you used in the text of report, generally at the end of the sentence it applies to. There is a minimum of two references for this report. Refer to “General Lab Report Instructions” for information/links on APA citations.
Figures & Legends
1) Post each picture you took here, after the references. Refer to each figure in the appropriate section of your paper (such as the Results) by number based on when you discussed these (i.e. Picture 1, Picture 2, etc.). Write a short description below it (legend), usually 1 or two sentences. Activity submission: Save the report as one file (pictures embedded) and upload it to the submission folder on the course website (preferably Word file, .doc .docx .rtf .pdf). You are always welcome to email a backup copy to the instructor. Typical submission is about 3 pages single spaced
Explanation / Answer
Objectives of the Experiment:
Demonstration of microorganism usage as a food processing machine:
(Example: Yogurt preparation using bacteria)
Introduction
Yoghurt is prepared from milk with the help of lactose fermenting culture medium. This culture contains microorganisms which digest the lactose sugar of milk and converts them into lactic acid. This process generates glucose and galactose as a product. Bacterial strain commonly used is Lactobacillus acidophilus. These cultures are easily available in health food and drug stores.
Kingdom-Monera
Division-Firmicutes
Class-Bacilli
Order-Lactobacillales
Family-Lactobacillaceae
Genus-Lactobacillus
Species- L. Acidophilus
In short, commercial yogurt preparations need the following step like
Treatment of milk before preparation (standardization, fortification, lactose hydrolysis).
Heat treatment and then maintain at incubation temperature.
Inoculation with starter
Incubation for fermenting.
Post-fermentation treatment (pasteurization).
Materials:
Equipment
Reagents
Method:
This step helps to destroy the undesirable contaminant microorganisms present in milk.
Consistency reached after the incubation period. Mixture stops flowing as the container is tipped slowly confirms that yogurt preparation finished.
Observation:
Liquid milk converted to Semi solid yogurt after incubation period. There is no change in colour. The thickness of mixture changed completely from liquid to semisolid.
Discussions
The use of micro organism performs the production of lactic acid. The process is dependent on the temperature, pH, amount of starter culture added etc.
The temperature is highly important factor. At low temperature, the culture grows very slowly to adequately acidify milk and to achieve a good texture where as the culture is killed if the temperature is too high. The window of proper fermentation is small, (42 ºC to 44 ºC).The temperature is raised up to 44 ºC, the rate of culture metabolism is higher, and the yogurt is sweeter. Faster growth also prompts the yogurt to set faster. But higher temperature is harmful.
pH of mixture is gradually goes down with the culture grows but after formation yogurt it should be kept in 4 ºC, otherwise overgrowth of culture turns the yogurt more acidic and poisonous.
Based on amount of starter culture the time of yogurt formation changed. Higher amount of starter culture need less time to convert milk to yogurt.
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