Reminder on Examination

Examination starts at 7:00pm to-night and takes 2 hours.

7 pm to 9 pm

Last minute question from student

Dear CCCCCC

They are discussed in the lecture and may be found in the Mindmaps.

Neurotoxin: Botulinum toxin is sensitive to heat

Stable toxin: heat stable toxins from Staphylocuccus aureus, in fact the toxins denature when heated but the denatured forms are more toxic

Most toxic toxin: Botulinum toxin is the most toxic natural toxin

Best,

HS Kwan

On Tue, Nov 4, 2014 at 10:08 AM, CCCCC wrote:

Dear professor,

      I have some questions about toxin. What is relate to neurotoxin sensitive to heat ?
What is heat stable toxin causing quick toxification?
And what is the most toxic toxin?

I can't find them in the notes and web. Thank you so much.

Regards ,

Microorganisms to know well for the Final Examination 20141030

Salmonella enterica
Salmonella Typhi
Salmonella Typhimurium
Salmonella Enteritidis
Escherichia coli

• -EAEC, EHEC, EIEC, EPEC, ETEC, DAEC 

• and the German "hybrid" of EAEC/EHEC

Vibrio cholerae
Vibrio parahaemolyticus
Campylobacter jejunii
Shigella species
Listeria monocytogenes
Clostridium perfringenes
Clostridium botulinum
Bacillus cereus
Staphylococcus aureus
lactic acid bacteria

Saccharomyces cerevisiae

Norovirus
Hepatitis A virus

You should know their biological characteristics, e.g. pH range, temperature range, and so on.

Answer to questions from a student 20141030

Dear ZZZZZ,

Answer to your question are placed under each question.

Best,

HS Kwan

From: ZZZZZ
Sent: Thursday, October 30, 2014 11:38 AM
To: hoishankwan@cuhk.edu.hk
Subject: questions about the FNSC5110 exam

Dear Prof.Kwan:

    Sorry to bother you.

    I would like to ask several questions about our mid-term exam of FNSC5110.

    1.whether we need to memorise the food-borne disease outbreak events，aerobic/anaerobic metabolism diagram and the disease flow diagram?

A: you should know the important outbreak events. You should also be familiarize with all materials discussed in the lectures.

    2.Will the topic of HACCP be covered in exam?Because little is mentioned in lectures.

A: No

    3.What topics of lectures will be the emphasis of exam that we need pay close attention to?

A: See list of important Foodborne disease causing microorganisms on the blog. Also the effect of various parameters on microbial growth and survival.

    Thank you.

Yours appreciatively,

Answer to questions from a student 20141029

Dear YYYYYYY,

There will be 2-4 short questions, and 2-3 long questions. Students can have a choice of long questions to answer.

Reading past papers helps you to know the style of the exam papers, but since the past papers are those of the course FNSC4180, some of the questions may not be covered in FNSC5110.

Understanding the materials covered in lectures, PPT, mindmaps and notes are important.

Best,

HS Kwan

From: YYYYYYY
Sent: Wednesday, October 29, 2014 2:31 PM
To: hoishankwan@cuhk.edu.hk
Subject: About the Final Examination 2014

Dear Professor Kwan,

Sorry to bother you again. 

Can you tell us how many short questions and how many long questions for this exam?

Also, if I look over the past paper, is it enough for cope with the examination?

Just worry about I don't have time to revision. 

Can you tell us main point for focusing?

I look forward to hearing from you.

Thanks & Regards,

Answer to the question from a student 20141029

Dear Professor Kwan,

Sorry to bother you.I am a student of MSc NFST.

Can you post the model answer for the following question? 

I think that we don't have tutorial in our lecture and don't know the correct answer. Thank you so much!

9. You are the senior technical manager of an apple cider bottling factory.  You are responsible for food safety management system ISO22000 based on HACCP.  The following happened last week: i.          On Tuesday, your technician rushed into your office and informed you that the quality control laboratory have made a mistake in measuring the pH of the apple cider  delivered yesterday for bottling.  The actual pH of the food was 4.5 and the laboratory used a malfunctioning pH meter and reported a pH value of 4.0.  ii.         Some of the apple cider was bottled and pasteurized already, using the pasteurization process designed for apple cider of pH4.0. iii.        The technician thought that the pasteurization process was not sufficient and suggested a corrective action that the bottled apple cider should be processed one more time for 10 minutes at 105°C. iv.        He provided you with the information from the quality control laboratory as described below.  v.         You had to judge whether the technician’s decision was correct or not and answer the questions below.
			Approximate microbial flora in apple cider (Number/ml)				Acceptable cell density in bottled apple cider(Number/ml)
Spoilage bacteria			1000				less than		0.0000001
Bacterial spores			100				less than		0.000001
Fungal spores			100				less than		0.000001

The problematic pasteurization process:     10 minutes at 105°C.

For apple cider:                                                                                                     

D values and Z values of the microbes at pH4.0:
	D value at 105°C(minute)	Z value(°C)
Spoilage bacteria	0.001	2
Bacterial spores	0.1	10
Fungal spores	0.002	5

D values and Z values of the microbes at pH4.5:
	D value at 105°C(minute)	Z value(°C)
Spoilage bacteria	0.01	5
Bacterial spores	2	15
Fungal spores	0.02	10

Answer the following questions.  Show your calculations :

a.            Calculate the F values set in the pasteurization for these target microorganisms?                                                                                 (1 marks)   At 105°C Spoilage bacteria: from 1000/ml to 0.0000001/ml -->10D=0.01min Bacterial spores: 100/ml to 0.000001/ml -->8D=0.8 min Fungal spores: 100/ml to 0.000001/ml -->8D=0.016min

b.            Calculate the number of D’s that actually occurred in the problematic pasteurization process for these target microorganisms?                                                            (2 marks)   Spoilage bacteria: 10min/0.01min=1000D Bacterial spores: 10min/2 min=5D Fungal spores: 10min/0.02min=500D

c.             Calculate the cell densities of the microorganisms in the processed apple cider with actual pH of 4.5 after they were processed for 10 minutes at 105°C?                                                                                                                                (2 marks) Spoilage bacteria: 1000/101000=10-997 (per ml) Bacterial spores: 100/105=10-3(per ml) Fungal spores: 100/10500=10-498 (per ml)

d.            Was the proposed additional pasteurization process needed and if needed, was it sufficient for the processing of the one-time processed apple cider with wrong pH measurement?  Explain briefly.                                                                                       (1 mark) Needed. Reason: Bacterial spores-->10-3/ml, larger than the acceptable level of 10-6/ml.       sufficient or not: additional 10 minutes at 105°C Bacterial spores at 10-3/ml for additional 5D reduction --> 10-3/ml x 10-5 =10-8/ml Sufficient

e.             Was the technician correct in his suggestion of the additional remedial processing?  If he was wrong, fire him and suggest alternative pasteurization time to treat the problematic bottled apple cider at 105°C.  Explain briefly.                                (1 marks) According to above calculation. The remedial processing should be sufficient. The technician was correct.

f.              Suggest a new process with a combination of pasteurization temperature and time for the remaining batches of apple cider (pH4.5).  These data may be useful for your consideration: heating for 10 minutes at 105°C for ten bottles of apple cider costs HK$1 and heating for 1 minute at 120°C for ten bottles of apple cider costs HK$5. Explain briefly your process with justification.   The current cost: HK$1 per 10 bottles=HK$0.1/bottle if 10 min at 105°C. Need to do it twice. So cost for the remaining batches would be HK$0.2/bottle. If we adjust the If increased to 120°C, time for pasteurization will need to be: D value for bacterial spores: one log decrease-->2 min to 0.2 min For 8D reduction target, the time needed will be 0.2min x 8=1.6min The cost at 120°C for 1.6 min for 10 bottles would be around HK$8  -->HK$0.8/bottle The process should be maintained at 20 min at 105°C for a lower cost.

I look forward to hearing from you.

Answer to questions from students 20141029

Dear LLLLLLLLLL,

The Answers are put under each question below. These Q&A will be posted on the blog also.

Best,

HS Kwan

-----Original Message-----
From: LLLLLLLLLLLL
Sent: Wednesday, October 29, 2014 10:51 PM
To: hoishankwan@cuhk.edu.hk
Subject: FNSC 5110 questions

Dear Professor Kwan,

I have several questions about the sample midterm that I have been struggling with, and it’d be great if you could clarify the following for me:

1. Calculation for attack rates

      Is the attack rate just basically the # of ill / total #

A: We have not discussed this topic in the class. Not included in the exam.

2. Question on the exam is: What are the F values set in the canning process for these target microorganisms?) I know that for low acid canned foods (pH>4.5), the calculation for F values is F = 12D. However, the exam asks for F values at pH 4.0 and 4.5. What approach should I take?

A: The F values now is set as the number of D attained in the process. If the process was designed for pH4.0, use the D for pH4.0 to calculate F.

3. Question on the exam is: What are the number of D's that actually occurred in the problematic canning process for these target microorganisms?

      I am not too sure about what the question is asking for. Dose it mean how many fold-decrease for each of the microbial (spoilage bacteria, bacterial spores, and fungal spores) occurred for 20 minutes at 105 degree C of processing (10 min per one time of processing, and the canned pig knuckles with incorrectly reported pH were processed twice) ?

A: Yes.

4. Question on the exam is: What would be the cell densities of the microorganisms in the processed pickled pigknuckles with actual pH of 4.0 after they were processed for 10 minutes at 105 degree C?

      Do I basically just calculate the number of fold-decrease using the known D value for microbes at pH 4.0, and then divide the approximate microbial flora in picked pig knuckles by the fold-decrease?

e.g. Spoilage bacteria (D value at 105 degree C) = 0.001 minutes

      That means there’s a 10-fold decrease in 0.001 minutes. So in 10 minutes, there is a 100,000 fold-decrease.

        Approximate spoilage bacteria in pickled pig knuckles = 1000/mL

      So 100,000 fold-decrease results in 0.01/mL after 10 minutes treatment at 105 degree C I felt like the calculations are wrong, because it happened that none of the microbial flora decreased to an acceptable cell density after treatment. Please let me know if I have misinterpreted anything.

A: Your calculation approach is basically correct. But 10/0.001=10,000, not 100,000. The decrease is log decrease, not fold decrease. A 10,000 log decrease of 1000/ml-->1000x10<-10>=10<-997> definitely blow the acceptable cell density. You need to know how to calculate.

Thank you very much for you attention, and I hope to hear back from you soon!

Best Regards,

Question on accessing the Univ Library exam paper link

Dear YYYY,

The link works well for me. Maybe you have to use computer on campus or use VPN to access it.

If you have problem logging in the link, please try log in to the University Library website>click on CUHK Exam Papers>search for FNSC4180.

Best,

HS Kwnan

-----Original Message-----
From: YYYY
Sent: Wednesday, October 29, 2014 10:15 AM
To: hoishankwan@cuhk.edu.hk
Subject: About the 4180 exam paper sample

Dear Professor Kwan,

Sorry to bother you.I am a student of MSc NFST.This morning I find I couldn't open the 4180 old examination paper sample,maybe the link has some problems.So would you mind have a check on it?Thank you.

Translating Bacterial Detection by DNAzymes into a Litmus Test Tram 2014 Angewandte Chemie Wiley Online Library

http://onlinelibrary.wiley.com/doi/10.1002/ange.201407021/full#.VDaSCTC4ipo.gmail