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Detecting Microbes in Food

1231 words (5 pages) Essay in Biology

18/05/20 Biology Reference this

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Detecting Microbes in Food


In this experiment, the purpose was to detect the number of microbes in different food samples from the final dilution for each. The hypothesis was that the growth of many microbes will be determined with this experiment using the Plate Count Agar. Using the Plate Count Agar there will be two highest amounts of microbes and there will be more microbes in milk than frozen food. The instructional materials that were used in this experiment were consisted of sterile water blanks, Petri dishes, pipettes, your choice of food sample, bottles of molten Plate Count Agar, and a blender to blend the different food samples. The results of this experiment showed that Raisins had the most amount of microbes and the Grapes had fewer microbes. In conclusion, This experiment actually applies to everyday life because microbes are everywhere and this experiment shows how much microbes can be on one food sample




Food Microbiology is the scientific study of organisms in contaminated food. This covers the major areas of concern like food spoilage, foodborne illness, and food production. That may cause diseases if food is uncooked, these foods are used to produce fermented foods. Fermented foods are some of the oldest consumed, Fermentation may provide characteristics to foods like yogurt, bread, cheese, and beer. Traditional fermented foods play a major role in the diet of many communities worldwide(Diaz, A. 2014). However, the foodborne illness also known as food poisoning is a major foodborne illness that have affected thousands of people over time like Salmonella. Salmonella causes approximately 155,000 deaths each year (Tadesse, G. 2014). As stated above, this report will detect the number of microbes in a food sample from the final dilution from each with the test materials of sterile water, a Petri dish, pipettes, different food samples, bottles of molten Plate Count Agar, and Blender. As stated above, the hypothesis determined that there will be more microbes in milk than frozen food and there might be two highest amounts of microbes. Milk is made up of proteins, fats, carbohydrates, vitamins, and minerals, providing an ideal environment in the growth of organisms. Raw milk is usually complex microbial community containing diverse organisms (Li, N.2018). Milk should have the highest amount of microbes because of food spoilage and being left out for so long. 

Material and Methods


In this experiment, 20 grams of food types were added in the blender mixed with 180mL of sterile water for 5 minutes. Each blended mixtures was distributed to their own petri dish. The first blended mixtures were distributed to 0.1mL into the petri dish labeled 1:100. Some of the blended mixtures were transferred to 1.0mL into 99mL of sterile water to create the 1:1000 dilation. The rest of the blended mixture was distributed to 1.0mL and 0.1mL from a 99ml bottle into a petri dish label 1:1000 and 1:10,000. Secondly, a bottle of media was collected to pour the media on the bottom of each dish. Allow media to solidify. Lastly, the dishes were placed into the incubator for 24 hours. The dishes were later collected from the incubator.   






During this experiment, observations were made in regard to the final dilution in different food types using media. Based on the number of Colonies forming units in the different food types the Raisins showed the highest amount of microbes in it and the Grapes showed the lowest amount of microbes. Due to the raisins being kept for a long time and the grapes were fresh also the raisins are high in sugar probably had an effect on the results. This plate count would not be used to access the safety of fermented food because the test result does not show any harmful bacteria. The hypothesis was incorrect. Below in figure 1. 

      Figure 1

Food Type

CFU per plate

Final Dilution

CFU per 20 grams of the food

Frozen Broc.




Fresh blueberries




Frozen blueberries




Fresh Broc.
















In this chart, are the different food sample that was experimented using the Plate Count Agar.




The main objective of this experiment was to detect which food type would have the most amount of microbes in it. The hypothesis that was tested was using the Plate Count Agar there will be two highest amounts of bacteria in the food samples. Throughout the data in this experiment, the hypothesis was found to be incorrect and it was actually only one highest amount of microbes and the lowest amount of bacteria. and milk actually had the second-lowest amount of microbes.  Based on the chart, Raisins were showed as the highest and Grapes were showed as the lowest amount of microbes when compared to other food types. This may be due to the Raisins being high in sugar and the been kept for and long time and the Grapes were fresh. In this experiment, it was necessary to serial dilution in order to be able to count the number of microbes on the food samples.  A possible improvement to the experiment to help reduce the number of errors would be to carefully read the methods and listen to your professor. Another improvement is to make sure you are putting the right amount of chemicals in your experiment.  This experiment actually applies to everyday life because bacteria are everywhere and this experiment shows how much bacteria can be on one food sample.


Literature Cited


  • Brown, A. (2007) Benson’s Microbiological Applications: Laboratory Manual in General Microbiology (9th ed.) New York, NY: McGraw-Hill.
  • Diaz, A (2019) Comparison of the microbial composition of African fermented foods using amplicon sequencing.
  • Li, N. (2018) Variation in Raw Milk Microbiota Throughout 12 Months and the Impact of Weather Conditions
  • Tadesse, G. (2014) A meta-analysis of the prevalence of Salmonella in food animals in Ethiopia
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