Questions about Final exam of 5110

Dear EEEEEE,

1. As mentioned in lecture, they will not be covered in the final examination.

2. The bacteria and their growth and survival.

Best,

HS Kwan

Sent from my iPad

On 5 Dec 2015, at 5:30 PM, EEEEE wrote:

Dear Prof.Kwan:

    

    I would like to ask 2 questions about our final exam of FNSC5110.

    1.Will the topics of HACCP, protazoa and parasitic be covered in the final exam? Because little was mentioned in lectures.

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

    Thank you. Have a good weekend~~

Regards,

Questions of last exam papers rwview

Dear AAAAA,

Please check the papers of FNSC3180 & 4180 for your reference.

Best,

HS Kwan

On 3 Dec 2015, at 5:36 PM, AAAA wrote:

Dear Prof kwan,

For the past exam review, I only see the paper of food microbiology but no paper of fndc5110. Can you advise which paper should I use for revision?

Thanks

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.

Some more questions from student via email

Dear Prof Kwan,

Thanks for your reply. But I have further questions as below. Please kindly
help. Thanks a lot.

1)It is known that the temp of thermophile C. perfringens is 42-47C, but how
about the temp range of mesophile C. botulinum?

A: C. botulinum has optimum temperature of 26-35C.

2)The endospore of C. botulinum is most heat resistant, nearly the last one to
die during cooking, but how come the neurotoxin(heat liable protein)it produced
cannot be eliminated by cooking(as need to be killed by canning which need much
higher temp)?

A: Canning aims to kill the C. botulinum endospores, not the neurotoxins. The neurotoxins are heat sensitive.

3)what organism is mostly grow in red wine based on below condition? (as
yeast/fungi seem cannot grow in high Aw (0.99))

Red wine:
Water Activity     0.99
pH                 4.5
NaCl content w/v           0.5%
Redox (mV)         350
Sugar content      Moderate
Protein content    Low
Keeping temperature 25C

A: Yeasts and fungi can grow at high Aw. Acetic acid bacteria can grow in red wine. But this group of bacteria was not covered in our lectures.

Note revisions in previous Q & A

Q: Culturing does not detected the pathogen in oysters in winter but the pathogen appears in summer to cause liver infection:_____

Your answer: V. cholerae

I am wondering whether or not V. cholerae could infect liver....

A: I missed the part on liver infection--so it should be hepatitis A

One more question from student via email

Dear Professor Kwan:
Sorry to bother you. I'm really confused about some questions of 5220.
1. causing severe food borne intoxication during famine?
I suggest maybe V. cholera because of famine but V. cholera is not intoxication.
So, I don't know the right answer.

A: not covered in this year's topics. The microbe is Aspergillus flavus, producing aflatoxin.

2. cats as second hosts and infections in immunocompromised people?
Is it Listeria?

A: not covered in this year's topics. A parasite.

3. Bread, 0.85Aw, 6.5pH, 1.0% salt, -50 redox, moderate sugar and protein, 25
temperature, what kind of bacteria exists in it?
Is Hepatitis A virus possible for this one?

A: Viruses can not grow in food. Aspergillus spp.

4. cabbage, 0.99Aw, 5.2pH, 0.5% salt, 350 redox, moderate sugar and low protein,
15 temperature, what kind of bacteria exists in it?

A: Many different bacteria can grow in this food.

Another question from student via email

Dear Prof. Kwan,

Excuse me, I have 2 questions about the answers you have just posted: 

1. Could Listeria monocytogenes really grow under pH=4.0 condition ?

A: Probably not, so note changes in the last reply

2. As Listeria monocytogenes is gram +ve, should I believe that it could grow under as low as 0.85 water activity condition?(I took this information from your lecture notes...)

A: 0.85 Aw is too low for L. monocytogenes to grow.

Thank you in advance =]

Questions from a student by email--Revision

Dear Prof Kwan,

I would like to ask below 5 questions. Please kindly advice. Thanks for your
reading & helping.

1.For fresh apple juice, the condition is acidic & high sugar & low salt & keep
at 25C. How could I determine whether it is yeast/ecoli 0157/lactic acid
bacteria (as all seems favour to this condition)?

A: Lactic acid bacteria: more competitive than E. coli and grow faster than yeast

2.For ground beef, the condition is high protein & salt& not acidic, if stored
at 25C, is it resulted as S. aureus? But if stored at 5C, it turns to be L.
monocytogenes?
But if it is high protein & store at 25C,but not salty & acidic,then it became
Ecoli 0157?

A1: Yes, S. aureus, if 5C, L. monocytogenes

A2: Yes, E. coli O157 should grow better.
3. From the pastpaper:
a)pls see attached picture, see if the organism is correctly stated (based on
highlighted reason)
b)the most toxic natural bacterial toxin -> C. botulinum?
c)Culturing does not detected the pathogen in oysters in winter but it appears
in summer to cause liver infection -> hepatitis A rather than V.cholera?

A (a) Go to the end of this post

A (b) Yes

A (c) Yes, hepatitis A.


4. S. aureus make the toxin become stonger if reheat the meat again,
so thats mean we cannot reheat something like sui mei that already cooked & put
in ambient temp (which contain S. aureus)?

A: Yes, the siu mei would still contains toxin

5. One of the controlled method of spore forming bacteria(C. perfringen & B.
cereus) is fully reheated the food before consumption. But it is known that
heating activate endospore to germinate, so why/ how could the food is still
considered to be safe once reheated?

A: The food reheated and then consumed right after reheating would activate endospores to germinate but they would not have enough time to grow and cause problem

Q3 A (a)

From left to right:

Listeria monocytogenes, Salmonella spp./E. coli O157:H7 is ok too, Aspergillus oryzae,

None (pH 4.0 and low temp, high salt), C. perfringens

Question on Hurdle Technology

Q: What is Hurdle Technology or Hurdle Theory of  foodborne microorganism control?

A: Go to Google Image and type in "Hurdle Technology" and find the right pictures.

Question on parboiled chicken

Q: In cooking of parboiled chicken, why is it so dangerous?

A: Chicken killed-->put in warm water to soften skin for defeathering [cross contamination, especially when water is not hot]--> defeathering[usually use the same machine for many chickens, cross contamination]-->cut up the chicken[cross contamination]--> cook in hot water below boiling temperature [ undercooking, Salmonella or other bacteria may survive]--> chilled in cold water[water may be warmed up, cross contamination, bacteria may grow]--> display in room temperature[bacteria may grow]--> eaten without cooking again as ready-to-eat-food [bacteria grown are not killed, bacterial loading may be high]--> foodborne infection

Question on Redox

Q: How to measure redox?

A: The principle is to carry out redox reaction and compare to a reference set.

From the notes: Redox measurements of pure chemicals are obtained by measuring the voltage
obtained when a mixture of oxidizing agent and its product [e.g. oxygen + water] is put into contact with a mixture of a reference pair of compounds [oxidized form + reduced form]. The reference set, by convention, is H+/H2  at pH 0. The direction of the reaction and the voltage obtained depends on which substance is the best oxidizing agent and how good it is relative to the other potential oxidizing agent in the mixture. If the oxygen/water pair is being evaluated, we will be comparing oxygen to H+. You can use the same system to measure the redox potential of a food. In this case, the food is substituted for the pair of pure chemicals to be measured, and it is measured against the standard reference set. 

Fermentation question

Q: When to use fermentation in place of respiration?

A: Should be referring to FACULTATIVE ANAEROBES that can carry out both fermentation and respiration. 
Respiration is used when there is usable electron acceptor present. 
Fermentation is used when there is no usable electron acceptor AND there is fermentable substrate. For example, fermentable sugar is needed for glycolysis.

Questions in Review Session

Q: How to calculate D values and Z values?

A: Use the semi-log paper and plot the values. Find the values for one log reduction

Q: How to use D values? 

A: For example, for canning of non-acid food that requires 12D reduction, calculate the time required for 12 log reduction: D value x 12.

Key: make sure the temperature used matches to the specific D value,  e.g., D 100  should be used if you are heating the food at 100 C.

Q: What is the use of Z value?

A: To calculate new D values when temperature is changed. So you can reduce the time needed for heat treatment. The main reasons for industry are, equipment suitability, time required, effect on food, and cost.

FNSC4180 Food Microbiology, Chinese Univ of Hong Kong, by HS Kwan: Past exam questions

Dear students,

Some questions raised inFNS4180 that may be related to FNSC5110.


http://fns4180hsk.blogspot.hk/search/label/Past%20exam%20questions

HS Kwan


Sent from my iPad