Unit 6 Assignment 3: Safely undertake the project, collecting,
analysing and presenting the results, Review the investigative
project using correct scientific principles:
Project implementation and review
How does the rate of bacterial growth become affected by different fat
contents in milk?
Testing the spoilage of milk in different fat contents:
Abstract: When the petri dishes were made using molten agar and adding
different dilutions of different types of milk to grow bacteria in. This was to
identify which type of milk grew the most bacteria to see if the fat contents of
the milk had an affect on the bacterial growth. It was found that from the
results semi-skimmed milk had the highest bacteria colonies. Skimmed milk
had the lowest number of colonies. The issue found with this method of
experiment was that it cannot be determined that the different amount of
bacteria colonies was due to the fat content of the milk as there is no official
test for that and the varied amount could have been by chance. This
experiment is to the public for people to know what milk they want to buy
based on how long they last with the fat contents if they are struggling what to
buy.
Introduction:
Hypothesis: The milk with the highest fat content will have the lowest number
of bacteria in it and the skimmed will contain the highest amount of bacterial
growth.
The hypothesis was incorrect as the semi-skimmed milk had the highest
bacteria colonies. Skimmed milk had the lowest number of colonies.
The new method was effective in how efficient it was. The change made this
method from the previous one was to add more equipment. They were small
things that would not change the results to the experiment, but they were
important changes as the test tube was needed for the pH meter’s probe and
three beakers were needed to pour the three different milk types into them. to
use the pH meter in them to record the pH before the milk was spoiled to
record if there was any difference in the three types of pH. The pH of the milk
could not be recorded after it had spoiled like hoped as this could be
dangerous opening bacteria filled milk petri dishes. Also, the fact that the
samples were in petri dishes meant that they would make it unable to record
,the pH of the different milk types as they were already diluted with the
distilled water and completely untraceable when the molten agar was added.
The method of using a probe to record the pH was not a good idea because of
this. If the method was changed, Using another method of recording the pH of
the milk after it had grown bacteria would be better, but it would have to be
completed in a separate experiment. In the new method the procedure was
completed in one day and reviewed the bacterial count on the fifth day
because there was realisation that the previous would gain too many numbers
of results counting the amount of bacteria each day so it was decided to count
them on one day which ended up being the fifth. They were counted on the
fifth day to allow enough time for bacterial growth fully.
https://newprairiepress.org/cgi/viewcontent.cgi?
referer=&httpsredir=1&article=3226&context=kaesrr#:~:text=in%20raw
%20milk.-,Milk%20fat%20content%20did%20not%20affect%20bacteria
%20counts.,protein%20degradation%20became%20more%20pronounced.
A comparison of results with published data:
This was an investigation completed by S. Zimmerman, I.J. Jeon, L. McVay who
studied Bacterial degradation of milk components is affected by storage
temperature and time. This relates to the investigation as they also tested if
the different fat contents had any effect on bacterial growth. The main
difference in their investigation was that the milk they used was raw which
mean it has not been pasteurised whereas the milk used in investigation was
pasteurised. This can have an effect to the results they achieved in their
investigation compared to the investigation as they could have a different
outcome to the investigation. In their investigation it was concluded that the
fat contents in the milk did not have any effect on how much bacterial growth
there was during the bacterial count. Another difference in their investigation
was that they stored the milk at a different temperature to what was done.
They had the temperature to 3.9 degrees Celsius for 4 days. They then
completed the bacterial count at the 8th day. In the investigation the petri
dishes were put in a 25 degrees Celsius incubator for 5 days. The reason for
them to use raw milk was due to its great ability to produce more bacteria
than pasteurised milk. From this study they suggest that the bacterial growth
rate was influenced by the time and temperature. The longer they left the milk
to spoil the more bacteria was produced. When the temperature of the milk
being stored in was increased more bacteria was produced. Bacterial counts
were done throughout the experiment but in the investigation, only one
bacterial count was completed at the end of the investigation which was the
fifth day. In their report they stated that the milk after day 2 when it was kept
, at 3.9 C degrees it could still be pasteurised and drank safely as any bacteria
produced was not harmful at that time. The milk that was kept at a higher
temperature on the second day would not be accepted as there would be
bacteria that can be considered dangerous to humans. The different fat
contents used in the experiment where different to the fat contents chosen for
the experiment. This can have an impact on the results to whether fat content
has an impact on the bacterial growth rate. From this we would not be able to
conclude if the fat content does impact it and this is comparable to the
experiment as they can only go as far to say that in the experiment, it was
found that it did or did not impact the bacterial growth rate. This means it
could not ultimately conclude the different fat contents in milk increases or
decreases the bacterial growth of the milk.
Another reference:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4095770/
This is information linked to the bacteria that was found in the experiment that
was completed. It tells what E.coli is and how it can be found in milk after it has
spoiled, it shows that lactic acid and fatty acid found in the milk is the cause to
the E.coli growing.
Methods:
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