Food Microbiology & Biotechnology Enzymes 代写

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  • 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:
     
     
     
         /10 marks
    Q2 By what percentage did pasteurisation reduce the count? Show your calculation.
     
     
         /4 marks
     
    Q3 Discuss the results you obtained in relation to the mean obtained for the class.
     
     
         /10 marks
     
     
    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.
     
         /8 marks
     
    1. In the context of this experiment, explain the role of each of these media in the enumeration and identification of coliforms and E. coli.
     
         /8 marks
     
    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.
     
     
     
         /10 marks
     
     
     
    Q6. Explain how the methods used selected for mesophilic and thermophilic spore-forming bacteria.
     
     
         /10 marks
     
    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.
     
     
         /6 marks
     
    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).
     
     
         /10 marks
     
    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 37oC 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.
                                                                                                        
     
    /10 marks
     
          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.
     
     
    /4 marks
     
    1. 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.
     
         
         /10 marks                                     
    Fig 1 gamma radiation

    Food Microbiology & Biotechnology Enzymes  代写