Microbiological Quality of Different Yogurt Brands


02 Apr 2018

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Andrea Roberta Martinez Zepeda


Which yogurt brand consumed in Nicaragua is healthier for the human body?


Believing that we are germ-free is an antiquate way of thinking. When you ask someone if they are free from germs one out of four people will answer yes.[1]Truth is that out body contains more than ten trillion germs in our intestinal tracks. There are more than 500 types of bacteria found in our intestinal tracks and there is no way to eliminate them so there is a constant war between these bacteria and beneficial microorganisms. To fight these bacteria we need beneficial organisms to help restore or maintain our health. There are foods that contain these beneficial organisms, such as fermented foods. According to the Merriam Webster Dictionary, fermentation is an anaerobic (without oxygen) breakdown of energy-rich component.[2] Fermentation implies the use of microorganisms to complete the process (zymology which is the science applied in this process), and can also be used as a preservation technique with the usage of lactic acid. Fermented foods are foods that after going through fermentation, its bacteria feed on the sugar and starch creating lactic acid. Fermentation creates many types of beneficial enzymes such as; vitamins, omega-3 and many others.

These organisms are called probiotics. The prefix word pro means forward & forth, therefore assuming it is in favor of our health. The suffix –biotic stands for caused by living organisms. The United Nation Food and Agricultural Organization (FAO) defines probiotics as “living microorganisms, which, when administered in adequate amounts, confer a health benefit on the host”[3] As the definition given says, probiotics have to be controlled in certain quantities to be effective on the person consuming them, so, where can they be found? Probiotics can be found in supplements and fermented foods such as yogurts, and dry sausages.

Yogurt as mentioned before goes through fermentation process but more specifically with the help of lactic acid bacteria lactobacillus bulgaricus and streptococcus thermophilus[4]. Theoretically the manufacture of yogurt should follow this process:

“The milk is firstly heat treated, homogenized and is then cooled to allow the addition of bacteria or starter culture. Given the right conditions, i.e. correct temperature and moisture, the bacteria are able to ferment the milk sugar (lactose), producing lactic acid. The milk proteins then coagulate and set, to form yogurt. A colorless liquid called acetaldehyde is also produced during fermentation and gives yogurt its distinct flavor “ (Danone Ireland)

As we already now yogurts are rich in probiotics and many other nutritional components. Three types of yogurt are going to be used; probiotic yogurts, bio yogurts and Nicaraguan homemade yogurts. Probiotic yogurts are those that contain cultures that aid body processes such as digestion. Some cultures this yogurts might contain are bifidus and acidophilus which produces body’s flora. Bio yogurts have a creamier and milder flavor. They might also contain probiotics such as BB-12. Nicaraguan homemade yogurts are made with milk and are left unrefrigerated at the environment's temperature. Since it is really easy to make, during this lab I will make my own to make sure it goes through the precise process and then test its microbiological features to find out whether it is the healthiest to consume or not. All types of yogurts are good since they are easier to digest than milk. Because of its bacteria they are a good source of phosphorus and calcium which is good for teeth and bones. But, how do we know which one is the healthiest to consume? As we speak of healthiest we refer to the yogurt with the adequate amount of probiotics, lactic acid and pH level and coliforms (bacterial indicator of sanitary quality[5]) We need to know some things about coliform bacteria to understand their importance in the manufacture of yogurt:[6]

  • Coliforms grow in aerobic conditions unless you give them the opportunity to grow in anaerobic conditions such as fermentation.
  • As they ferment lactose, they will ferment glucose as well. (if coliform ferments a sugar it is assumed it at least ferments glucose)
  • There are no genus or species classified as coliforms
  • Coliform bacteria such as lactobacillus bulgaricus and streptococcus thermophilus belong to the positive strains of Escherichia coli.
  • Bacteria that belong to negative strains of coliform and causes illness do not ferment lactose.

Due that yogurt consumption has increased since 1980, there have been created many machines to produce yogurt. During this lab we will be observing which yogurt brand is better for the human body. To determine which yogurt is healthier, we have to consider the storage, transportation and commercialization of the product. To determine which brand is healthier we will use microbiological standards established by FAO in association with World Health Organization are going to be used to verify the yogurt’s pH level, coliforms quantities and lactic acid bacteria.

The objective of this lab is to evaluate the microbiological quality of different yogurt brands available in Nicaragua’s market. The yogurt brands being tested are Eskimo, Yes, Dos pinos, and a Nicaraguan homemade yogurt. In order to find out which yogurt brand is healthier to consume I will leave yogurts incubating for five days at a 35 degree C temperature. After the five days pass, with the help of a microscope I will test how much coli form bacteria yogurt has. As mentioned previously, coliform bacteria can ferment lactose at a certain temperature which the result is yogurt. This happens due to anaerobic respiration since glycolysis breaks down molecules of glucose into two molecules of pyvurate in the cytoplasm. As we know cell respiration releases energy from carbohydrates and lipids[7]. If yogurt does not have the right type of coliform belonging to Escherichia coli, it may cause a disease which will be bad for the human body. This factor will be tested by coliform bacteria testing which will be done in a lab and then I will compare quantity results. Yogurt has to have a certain amount of yeast to consider it healthy and hygienic to consume, if it has more yeast than expected it is considered to be unhygienic to consume since its bacteria are starting to die. Since its bacteria die, the good effects caused by probiotics are no longer present, making no difference with yogurt and regular milk.

Another factor to be considered to determine which yogurt is healthier for the human body is the pH level the yogurt has after being incubated for five days. Plain yogurt has a pH level between 4 and 4.5, it is considered to be low acidic. The problem is when sugars are added to it because it increases its acidic level which makes it dangerous for the human body. Sweetened yogurt’s pH should stay between 6 and 7 to maintain a balance of the body and pH level. I will test this factor by using pH strip test on yogurts. If the yogurt surpasses pH 7 then it would not be recommended to take since it might hurt your organs since it has a higher pH level than the one it can take.

Now that we know all the background information about what aspects will be evaluated, what will be considered healthy? To be healthy it must have min 107 colony-forming unit per gram. [8]Since we are going to test 15 g, it should have 15x107 colony forming. As well, yogurt must have min. 106 labelled microorganisms (probiotics) per gram. These standards apply for only the fermented milk. As we speak of microbiological aspects, I will follow standards established by principle for the establishment and application of microbiological criteria for foods.[9] I will consider production date, conservation and as mentioned before colony forming. pH level will also be measured and it will be considered healthy a yogurt with a pH level between 4.5 and 6.

Hypothesis: If we test yogurt to obtain healthy microbiological results then Nicaraguan homemade yogurt will have the healthiest results because it has a controlled pH level, and goes through a natural fermentation process without the involvement of artificial procedures. Variables: Independent variables: Different yogurts to be tested

  • Probiotic Yogurt, strawberry flavor from Eskimo
  • bio yogurt, strawberry flavor from Yes
  • natural yogurt, plain, from dos pinos
  • homemade Nicaraguan yogurt a.k.a "leche agria"

Dependent variable: Microbiological results

Controlled Variable: When incubating yogurts:

  • same fridge temperature
  • same amount of time left on the freezer
  • same amount of yogurt
  • same production date

When making homemade yogurt:

  • Same environment temperature through fermentation process
  • Same container
  • Accuracy when placing milk
  • Measure time left (6 to 8 hours) Materials:
  • 150 g of Yogurt (different brands: eskimo, yes, dos pinos)
  • 150 g of homemade Nicaraguan yogurt
  • Pipette
  • Thermometer
  • Teaspoon
  • Kitchen burner
  • Light microscope
  • petri dish
  • pH strips
  • goggles
  • gloves
  • coliform test
  • Freezer
  • Containers
  • Balance
  • saucepan
  • Yogurt starter
  • Crock pot
  • beaker


To make homemade yogurt:[10]

  1. Turn crock pot on at a low temperature, this is because it has to be at the right temperature when you place the milk. During this step also take out the yogurt starter so it can warm a little before mixing it with the milk.
  2. Pour 1 liter of milk into a sauce pan at medium temperature, stirring occasionally until it reaches 185 degree Celsius. (Check temperature with a thermometer to make sure it reaches 185 ºC)
  3. Once milk reaches 185º C bubbling (meaning it is boiling), remove from the burner and put it in a sink half full of cold water.
  4. Let the milk cool down, and stir it occasionally.
  5. Measure yogurt starter in a bowl and then pour 1 cup of milk, mixing it. (use two teaspoon per 4 cups of milk)
  6. Put the rest of the milk and yogurt starter in the crock pot.
  7. Put the lid on, and put a heavy towel on top. Leave it there for around for 6 to 8 hours.
  8. After the milk placed in the crock pot stops culturing, put the pot in the freezer and let it cool. Make sure not to shake or mix the yogurt since it will not help it maintain its shape.
  9. After the yogurt is cool, you can put it a jar and refrigerate it up to 14 days.

When incubating yogurt for five days:

  1. Measure 200 g of the different types of yogurts in the beaker
  2. Once measured, put 150 g of yogurt in glasses and put them at a freezer with a temperature 15 ºC.
  3. Leave the yogurt there for five days; make sure the temperature remains constant.
  4. After the five days, re measure the 150 g in the beaker.
  5. Prepare for pH strip testing.

Word Count: 1819

Work Cited

[1]Survey in 11th IB students from Notre Dame School

[2]Merriam Webster English dictionary, Fermentation, <http://www.merriam-webster.com/dictionary/fermentation>

[3]Taken from book “probiotic foods for good”

[4]Bacteria, responsible for milk fermentation

[5]Merriam Webster English dictionary, coliforms, http://www.merriam-webster.com/dictionary/coliforms.

[6] Facts taken from http://www.splammo.net/bact102/102coliforms.html

[7] Taken from Cambridge University Press, Biology for IB diploma

[8] Standards taken from World Health Organization see the table in Appendix 1

[9] Standards found in Appendix 2

[10] Process taken from


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