BIO2041: Lecture 4 Simms

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  • Created by: LMoney
  • Created on: 14-05-14 12:05
what 3 processes are used in high temperature processing of food?
1) Low heat processing (Pasteurisation) 2) High-heat processing (Appertisation) 3) Microwave Heating
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what 2 processes are used in low temperature processing of food?
1) chill storage 2) freezing
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when microbial cells are killed what rate do they die at?
exponential rate
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what kind of curve comes about from plotting the log of the number of surviving cells?
Straight line
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what is the D value?
Decimal reduction time- time at any given temperature for a 90% reduction in cell survival to be achieved
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what is a 90% reduction equivalent to?
1 log cycle
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if the cells are being killed faster- is the D value lower of higher?
Steeper slope and lower D value
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what does the D value tell us?
The D value gives information about relative heat resistance of microbes- given as DT where T is the temperature in ºC
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what happens to the D value as temperature is raised?
D value decreases exponentially
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what curve is obtained when logD is plotted against temperature?
straight line w/ negative slope
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what is the Z value?
the temperature increase required to increase the death rate 10-fold (ie. Reduce the D value by 10-fold or by 1 log value)
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the 12D concept is used to destroy the heat resistant spores of which organism?
Clostridium Botulinum
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what is the F value?
time (min) needed to completely destroy a specific number* of microbial spores at a reference temperature (121.1 ºC)
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what is the P value?
P value – time (min) needed to completely destroy a specific number* of microbial cells at a reference temperature (60 ºC)
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what are the factors that determine the effect of heat on microbes?
1) Stage of growth 2) Growth temperature 3) pH 4) Fat, protein 5) Aw
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which stage of growth is more heat resistant?
stationary
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will higher or lower growth temperature make microbes more heat resistant?
higher growth temperature means more heat resistant
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what pH are microbes most heat resistant at?
more heat resistant close to optimum pH for growth
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do higher fat and protein contents increase or decrease resistance?
increase heat resistance
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does a reduction in Aw increase or decrease heat resistance?
reduction in Aw increases heat resistance
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what is the objective of pasteurisation?
to reduce by a set amount the vegetative cells of pathogens (and a large number of associative spoilage organisms – yeasts, moulds, bacteria, viruses)
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what log reduction is usually aimed for in pasteurisation?
6 log (6D) reduction
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in pasteurisation, the temperature is below what level?
100C- usually in range of 60-80
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is there a single temperature for pasteurisation?
No single temperature for pasteurisation as it is heat effect – temp x time
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what needs to be taken into account in pasteurisation?
both D and z
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what organism was pasteurisation originally invented to target?
Mycobacterium tuberculosis, then designed to destroy Coxiella burnetii which causes Q fever (more heat resistant)
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what does LTLT stand for and what does it mean?
LTLT (Low Temperature Long Time) method – 62.8 ºC for 30 min
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what does HTST stand for and what does it mean?
HTST (High Temperature Short Time) method – 71.7 ºC for 15 sec
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are all microbes destroyed by pasteurisation?
no- so must use appropriate post-pasteurisation conditions to minimise growth of the survivors to prevent spoilage
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is the phosphatase enzyme present in milk more or less resistant to heat than Coxiella burnetii?
More resistant
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after mixing milk with PNPP substrate, if enzyme is active PNP is released which is what colour?
yellow
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what concentration of PNP is acceptable?
Under standard conditions must have less than 10 mg PNP produced/ml pasteurised milk
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methylene blue and resazurin are what type of indicators?
redox indicators
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if they are blue what does it mean, and what if they are colourless?
Blue = oxidised and colourless = reduced
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If the indicator is decolourised within what length of time, does this indicate incomplete pasteurisation?
30 min
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who was appertisation named after?
Nicolas Appert- started experimenting with methods for preserving foods in 1790s in France
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what is the objective of appertisation?
destroy microorganisms that will grow in the food under normal storage conditions- destroys all vegetative cells and some spores
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Spores of some thermophilic bacteria may survive appertisation but will not germinate unless storage temperature is above what?
30C- Once germinated they continue to grow and spoil food even if storage returned to
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what are 2 common appertisation processes?
1) canning 2) Ultra heat treatment (UHT)
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what are the steps of canning?
1) Food prepared (washed, peeled, chopped, etc) 2) Put into sealed, airtight containers (cans, bottles, retort pouches) 3) Heated with pressurised steam to 116-121 ºC 4) Cooled, stable for many months/years
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Canning aims to reduce the number of organisms by how many log reductions?
6-12 log reductions (6-12D)
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what is the main target of canning if pH of food > 4.6?
Cl. botulinum
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when is ultra heat treatment used?
where heat (temperature x time) would have an adverse effect on the product
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what are some example of foodstuffs that heat would have an adverse affect on?
milk, fruit juice, salad dressings, baby food, tomato products, soups
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what temperatures and times are used in UHT?
138-142C for 2-3 seconds
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what is the shelf-life of UHT treated products?
3-6 months
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what could happen in UHT to cause spoilage?
heat stable enzymes could survive
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what is microwave heat?
form of radiation, induces oscillation in water molecules due to increased kinetic energy, energy transmitter to molecules in contact with water- generates heat by friction, temperature can get very high, lethal for microbes
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what is the main disadvantage for microwave heating?
difficult to get uniform heating so potential for pathogens to survive, not widely used industrially for preservation
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cous
cous
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Card 2

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what 2 processes are used in low temperature processing of food?

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1) chill storage 2) freezing

Card 3

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when microbial cells are killed what rate do they die at?

Back

Preview of the front of card 3

Card 4

Front

what kind of curve comes about from plotting the log of the number of surviving cells?

Back

Preview of the front of card 4

Card 5

Front

what is the D value?

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