Questions from a student

-----Original Message-----

From: LLLLLLLL

Sent: Sunday, 22 April 2018 7:12 PM

To: HS Kwan, Prof. (SLS) <hskwan@eservices.cuhk.edu.hk>

Subject: FNSC3180 questions

Dear Mr Kwan,

         I would like to ask some questions.

1. From Past paper 2014-15, are these answers correct? If not, what are the answers?

    B1(b)(vii) Microaerophilic pathogenic bacteria commonly found to be related to poultry: Campylobacter jejuni

             (x)  Endospors germinate in overnight rice before frying:  Bacillus cereus 2. 'There is no universal STERILIZATION process.The time/temperature specified for a given food depends on which microbe you are trying to kill and the details of its heat resistence in that food.'' Is this statement correct?

3. From Past paper 2016-17, are these answers correct? If not, what are the answers?

     A2(C)Why is the growth inhibitor used during the recovery period at 37  °C?

               Growth inhibitor inhibits growth so as to ensure that cells counted are not due to cell growth. We want to count cells that are not killed and those recover from injury. Without growth inhibitor, more cells will be counted and the answer will be overestimated.

4. A3(iii) Add salt to 10% AND store food at 40  °C: Clostridium perfringens:  K because salt concentration is too high for it.

          (iv)Dry food to water activity of 0.85 AND store food at 25  °C:Clostridium perfringens: NG and S. Because it grows when food is held very warm (45-50 °C)for several hours,it does not grow at 25°C.

5. A4 Soy sauce chicken: Samonella enterica(common in chickens)

          Ground beef salted:Listeria monocytogenes(salt tolerant and psychrophile)

          Stuffing of roasted chicken:Clostridium perfringens(common in turkey)

          Bagel: Saccharomyces cerevisiae(yeast in fermentation of bread)

          Pickled Pork Knuckle:None(high salt con., very low pH) 6. B2 Is the microorganism involved Norovirus??? Pizza has the highest attack rate difference and incubation period of Norovirus(12-24 hrs)is more consistent with that of disease(lunch:25-52hrs and dinner:18-45 hrs). Incubation period of Staphylococcus aureus and  Clostridium perfringens are too short for the disease in this case. Am I correct?

   Please answer these questions as they are very important. Sorry for bothering you. I look forward to receiving your reply. Thank you.

Answers

1. Correct

                2. Usually we just refer to pasteurization: . 'There is no universal PASTEURIZATION process. The time/temperature specified for a given food depends on which microbe you are trying to kill and the details of its heat resistance in that food.'' STERILIZATION should be the same.

                3. Correct

                4. A3(iii) Add salt to 10% AND store food at 40  °C: Clostridium perfringens:  K because salt concentration is too high for it.---K is incorrect, should be S

          (iv)Dry food to water activity of 0.85 AND store food at 25  °C: Clostridium perfringens: NG and S. Because it grows when food is held very warm (45-50 °C)for several hours, it does not grow at 25°C.

                           Incorrect, should be G and S. C. perfringens is a thermophile.

                5.  A4 Soy sauce chicken: Samonella enterica(common in chickens)--Should be None

          Ground beef salted:Listeria monocytogenes(salt tolerant and psychrophile)---correct

          Stuffing of roasted chicken:Clostridium perfringens(common in turkey)---correct

          Bagel: Saccharomyces cerevisiae(yeast in fermentation of bread)--incorrect, should be Aspergillus

          Pickled Pork Knuckle:None(high salt con., very low pH)--correct

                 6. B2 Is the microorganism involved Norovirus??? Yes