Food Microbiology & Biotechnology Enzymes  代写


Laboratory Worksheet (100 marks)
 
Student Name:
Matriculation Number:
 
Section 1:
This section is based on Experiment 1.1 - The effect of pasteurisation on the total count of milk
Q1 Complete the following Table

	Your Individual/Group Results
	Dilutions (giving 30-250 colonies)	Colony count	Viable Plate Count (CFU/ml)*	Mean + S.D. (based on class results)
Raw milk
Pasteurised milk

*You should have just one final calculation for the viable plate count for raw milk and for pasteurised milk.
 
For raw milk only, provide all the calculations here:
 
 
 
Q2 By what percentage did pasteurisation reduce the count? Show your calculation.
 
 
 
Q3 Discuss the results you obtained in relation to the mean obtained for the class.
 
 
 
 
Section 2:
This section is based on Experiment 2.1 –Enumeration of coliforms/E.coli in mussels/shellfish
Q4 This experiment involves the use of three types of culture media: Differential Medium, Selective medium, and Selective & Differential Medium.

1. Explain the difference between these categories of media, and for Minerals Modified Glutamate Medium, Brilliant Green Bile Lactose Broth and Tryptone water with MUG, explain to which category they belong.

 
 

2. In the context of this experiment, explain the role of each of these media in the enumeration and identification of coliforms and E. coli.

 
 
For Q4, you will be expected to undertake some independent research and to cite the sources of your information.
 
Section 3:
This section is based on Experiment 2.2–Endospores of spoilage organisms in raw sugar
Q5. The objective of this experiment was to determine the presence of endospores of mesophilic and thermophile spoilage bacteria present in raw sugar or molasses. Briefly comment on the results you obtained.
 
 
 
 
 
 
Q6. Explain how the methods used selected for mesophilic and thermophilic spore-forming bacteria.
 
 
 
Section 4:
This section is based on Experiment 4.1–Thermal destruction of Escherichia coli in beef and chicken
Q7Present the data that you/your group obtained for this experiment in the form of a Table.
 
 
 
Q8 Use the dataobtained, to determine the D-value for the meat samples/temperatures that you have tested and comment on the significance of the data obtained. Please ensure that you clearly demonstrate how you determined the D-value (you have covered this in tutorials in weeks 2 and 4).
 
 
 
Q9The effect of gamma radiation on survival of endospores of Clostridium botulinum.
The use of gamma radiation is of interest in the sterilisation of foods that are sold raw (uncooked), for example prawns, vegetables and fruit.
Experiments were performed to examine the effect of gamma radiation on the death of endospores of Clostridium botulinumduring gamma radiation treatment in fish sauce. Samples of heat sterilised fish sauce, cooled to 23 ^oC and saturated with sterile nitrogen gas, were inoculated with endospores of Clostridium botulinum at a level of 1.0 x 10⁵ endospores ml^-1 and irradiated with various intensities of gamma radiation for up to15 minutes. After irradiation viable counts were performed by plating replicate 0.1 ml volumes of suitable dilutions of the sauces onto Clostridial Agar plates and counting colonies after 24h incubation at 37^oC in an anaerobic atmosphere. Viable counts were expressed as colony forming units (cfu) ml^-1. Results were as follows:

Radiation intensity 0.40 kGy min-1	Viable Count CFU.ml-1		Radiation intensity 0.55 kGy min-1	Viable Count CFU.ml-1		Radiation intensity 0.70 kGy min-1	Viable Count CFU.ml-1
0	1.0 x 105		0	9.9 x 104		0	1.0 x 105
5	2.4 x 104		5	5.4 x 103		5	4.4 x 102
10	5.2 x 103		10	3.8 x 102		10	2.3
15	1.5 x 103		15	2.5 x 101		15	Not detectable

                               

Radiation intensity	D-values
0.40 kGy min-1	7.5
0.55 kGy min-1	4
0.70 kGy min-1	2.1

 
             i) What is the relationship between gamma radiation dose and death rate of endospores of Clostridium botulinumduring gamma radiation treatment in fish sauce?
                Give a clear and complete explanation of your answer.
                                                                                                    
 
 
      ii) By what percentage is the population of viable endospores reduced after 5 minutes irradiation at intensity 0.40 kGy min^-1? Show your calculation.
 
 
 

3. Experiments were performed to examine the combined effect of oxygen and sodium chloride on the death of endospores of Clostridium botulinumduring  gamma irradiation. Normal fish sauce saturated with nitrogen gas and fish sauce containing 1.0% (w/v)  sodiumchloride and saturated with oxygen were inoculated with endospores of Clostridium botulinum at a level of 1.0 x 10⁵ ml^-1. The sauces were then irradiated with gamma radiation at an intensity of 0.40 kGy min^-1 for up to 15 minutes. After irradiation viable counts were performed as described above. Viable counts were expressed as colony forming units (cfu).ml^-1. The results are shown in Fig. 1 below.

                Would it be valid to conclude from the results shown in Fig. 1 that oxygen increases the death rate of endospores of Clostridium botulinum during gamma irradiation?  If your answer is that such a conclusion is not valid, what additional experiments would need to be performed in order to make such a conclusion valid? Give clear explanations of your answer.
 
     


Food Microbiology & Biotechnology Enzymes  代写