Section
A. Answer question 1,
2, and 3, and
any ONE question from questions
4 and
5.
Answer Question 1,2 and 3.
(15 marks)
1.
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Draw
a simple labeled diagram to illustrate the pathogenic mechanisms of the
"hybrid" Escherichia coli in the infection of intestinal cells. The
"hybrid" E.coli refers to
the one that caused serious EHEC outbreak in Germany last year, 2011.
(4 marks)
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2a.
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Describe the approach that we can use
to evaluate and predict the spoilage of foods.
(3 marks)
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b.
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Write short notes on Vibrio
chlorae and Vibrio parahaemolyticus
(5 marks)
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3.
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An
epidemiological analysis hypothesized that over the years there is a correlation
between the control of Salmonellosis in Chicken by Salmonella serotypes and the increased occurrence of human Salmonellosis
caused by Salmonella serotypes. Based on that hypothesis, answer the
following questions.
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a.
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Indicate which of the
answers correctly describes the trend curves and descriptions of chicken and human Salmonella cases. (1
mark)
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Figure
1. Changes in the number of cases of Salmonellosis
from 1935 to 1989
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i.
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National Poutry Improvement Plan (USDA)
started in 1935 and S. Pullorum
cases in chicken dropped over the years but S. Typhimurium cases remained at similar levels since 1962
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ii.
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National Poutry Improvement Plan (USDA)
started in 1935 and S. Pullorum
cases in chicken dropped over the years but S. Enteritidis cases increased since 1962
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iii.
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National Salmonella Surveillance Program
started in 1935 and S. Pullorum
cases in chicken remained at similar levels over the years but S. Enteritidis cases increased since
1962
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iv.
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National Salmonella Surveillance Program
started in 1935 and S. Typhimurium cases
in chicken decreased over the years but S.
Pullorum cases increased since 1962
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v.
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National Poutry Improvement Plan (USDA)
started in 1935 and S. Enteritidis cases
in chicken decreased over the years but S.
Pullorum cases increased since 1962
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i and iii
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ii and iii
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iii and iv
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i and ii
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i and v
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b.
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According to the hypothesis, the
control of Salmonellosis in chicken has an impact on Salmonellosis in human.
Which of the following factors would be important for the trends indicated in
Fig.1? Explain your answer briefly. (2 mark)
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Humans become more susceptible because
they have been eating more undercooked chicken over the years
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Humans become more susceptible because
their immunity are weakened over the years due to greater prevalence of AIDS
and other immuno-compromising diseases
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The antibodies produced in chicken in
Salmonellosis against S. Pollorum prevented
the growth of S. Typhimurium in
chicken after chicken Salmonellosis was under control.
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The antibodies produced in chicken in
Salmonellosis against S.
Enteritidis prevented the growth of S.
Pullorum in chicken before chicken Salmonellosis was under control.
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The antibodies produced in chicken in
Salmonellosis against S. Pollorum
prevented the growth of S.
Enteritidis in chicken before chicken Salmonellosis was under control
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Answer JUST ONE
of the following Questions.
(10
marks)
4.
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Indicate ONE of the organisms that may most preferentially
grow (the one most suitable to grow), among all organisms listed, in the food with the particular
characteristics and storage condition.
If none of the organism can grow, put in None.
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(10 marks)
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i.
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Polio virus
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ii.
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Clostridium
botulinum
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iii.
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Listeria
monocytogenes
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iv.
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Salmonella species
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v.
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Aspergillus oryzae
(fungus)
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vi.
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Saccharomyces
cerevisiae (yeast)
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vii.
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Norovirus
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viii.
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Escherichia coli O157: H7
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ix.
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Clostridium perfringens
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Soy Sauce
Chicken
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Raw
Cleaned Chicken
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Sweet Bread
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Pickled Pork Knuckle
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Stuffing
of roasted Chicken
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Water
Activity
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0.90
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0.95
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0.85
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0.97
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0.95
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pH
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5.2
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6.5
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5.0
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4.0
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6.2
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NaCl
content w/v
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9.0%
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0.5%
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0.5%
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9.0%
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2.0%
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Redox
(mV)
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-50
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200
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200
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150
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-200
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Sugar
content
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Moderate
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Moderate
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Moderate
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Low
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Moderate
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Protein
content
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High
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High
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Low
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High
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Moderate
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Keeping
temperature
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25C
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25°C
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25°C
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4°C
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40°C
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Handled by hand
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Yes
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Yes
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No
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No
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Yes
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Organism
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9.
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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 pH 4.0.
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.
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Approximate microbial
flora in apple cider (Number/ml)
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Acceptable cell density
in bottled apple cider (Number/ml)
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Spoilage bacteria
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1000
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less than
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0.0000001
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Bacterial spores
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100
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less than
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0.000001
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Fungal spores
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100
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less than
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0.000001
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The problematic pasteurization
process: 10 minutes at 105°C.
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For apple
cider:
D
values and Z values of the microbes at pH4.0:
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D
value at 105°C (minute)
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Z
value (°C)
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Spoilage
bacteria
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0.001
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2
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Bacterial
spores
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0.1
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10
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Fungal
spores
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0.002
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5
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D
values and Z values of the microbes at pH4.5:
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D
value at 105°C (minute)
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Z
value (°C)
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Spoilage
bacteria
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0.01
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5
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Bacterial
spores
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2
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15
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Fungal
spores
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0.02
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10
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Answer the
following questions. Show your
calculations :
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a.
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Calculate the F values set in the pasteurization for
these target microorganisms?
(1
marks)
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b.
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Calculate the number of D’s
that actually occurred in the problematic pasteurization process for these
target microorganisms? (2 marks)
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c.
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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)
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d.
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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)
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e.
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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)
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f.
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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.
(3 marks)
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- END
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