Biology 代写 不同类型牛奶发酵率

CONCLUSION:

When I began the experiment I assumed that if I started measuring the pH changes of the milk WITHOUT the Thermophilic starter culture then measure the pH of the milk WITH the Thermophilic starter culture and use the time interval between the next reading as a scope that would be able to eliminate the chance of any bacteria/ Thermophilic starter culture to be caught in the probe as I would make sure that I sterilized the probe with distilled water each time after I took pH values of the milk and note the expected pH of the distilled water (when I placed the pH probe in the distilled water).

The inconsistency of the results obtained during the experiment and the assumptions made before came from the rate at which the individual milk types ferment. I had previously assumed that the rate of fermentation of each individual milk type would be fastest in the Unpasteurized milk then the Pasteurized milk and then followed by the UHT milk due to their different (or lack thereof) heat treatments they had undergone through. My experimental results contradicted the theory behind it leaving my experiment with a number of flaws that could have caused this contradiction.

From research, when UHT milk is left in open air it will spoil and this is actually a condition the UHT milk processors state on their packaging and as long as the UHT milk is sealed it will not spoil. However this probably doesn’t explain why it fermented as fast as it did. The only possible explanation for this would have been that there was contamination between the samples caused by the use of the pH probe, ineffective sterilization or very rapid entry of bacteria from the air. I could distinguish between these possibilities by repeating with a more effective sterilization technique.

I will now look at the possible weakness and improvements that could be used to improve this experiment.

WEAKNESSES AND LIMITATIONS

IMPROVEMENTS

Distilled water was used to clean the pH during the experiment and this could have proved inefficient this is because the bacteria/culture that was on the pH probe wouldn’t have been killed in between pH measurements.

Use of alcohol/ ethanol as a form of sterilization. One would need to use 70% ethanol mixed in 30% water because the water helps to penetrate the bacteria cell wall around the pH probe. If one uses 100% ethanol, the bacterial cell wall could resist the effect of the ethanol.

Use of 1 pH probe during the experiment due to the fact that the laboratory only had 1 that I could use at the time. This made taking pH readings and measurements difficult as I had to keep sterilizing the probe all the time. This also increased the chances of contamination in the milk.

The use of at least 6 pH probes so as to find the pH changes for the 3 milk samples with the culture and the 3 milk samples without the culture. This would avoid contamination of the culture to the milk samples without the culture and also cross contamination between the different types of milk. These pH probes would need to be calibrated using the same standard solution so as to increase result accuracy. Or running the trials successively which would greatly reduce the chances of contamination

Lactose content wasn’t stated on the different types of milk and this proved to be a problem because lactose content does affect the rate at which milk ferments. Higher lactose content in one of the milks results in the increase in the rate of fermentation and vice versa and this could have had a clear effect on my results.

Use milk types that have an indication of the lactose content in them. Also if the lactose content isn’t specified I could measure the lactose content by the use of a polarimetry.

The different milk types were taken from 3 different dairy plants. This could affect my results in the experiment as these milk types would have gone through different methods of heat treatments some more extreme than others and also using different types of cows to produce these milks

I could have obtained the different milk types from the same dairy plant making sure that the same cow was used to obtain the milk before any kind of heat treatment occurred. Also I could have done the heat treatment myself and be as accurate as possible to heat to the accepted temperatures. The only limitation with that is that the UHT milk goes through such a high heat treatment that it would be difficult to heat the milk that high temperature.

Immediately the culture was added it was difficult to take the pH measurements and it meant that some of the milk samples had a ‘head start’ in the fermentation process.

This would have been improved with the use of the 6 pH probes I mentioned earlier.

There were some successes during the experiment such as how I managed to keep the temperature of all the milk samples the same using a water bath. Also the general prediction that milk would ferment fastest with the addition of the culture was supported

However some questions remain unanswered even after the amount of research I did, eg, was there contamination? Where did it come from and how did it affect my results. I couldn’t find a good enough explanation for the fluctuation of pH during the experiment. During my research the process of putrefaction came up as a cause for the fluctuations but I didn’t understand how the decay process could be involved in the fermentation processes as I would assume that it would only occur after the fermentation process is complete. This is one of the phenomena’s that I didn’t understand and I’m hoping that with this Extended Essay I could inspire someone to explore the possible answers for it.

Biology 代写 生物论文代写