Pasteurisation Flashcards

1
Q

Heat Preservation

A
Destroy pathogens
reduce and eliminate microbial
Enzyme Activity
Extend shelf life
With minimal damage to nutrients and sensory components
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2
Q

Temperature Vegetative state die at

A

60 degrees

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3
Q

Spore state die at

A

Survive above 100 degrees

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4
Q

Heat effect on food

A

Colour and taste effects canned meat, fruit and veg and milk

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5
Q

Canned meat colour and taste

A

Oxymyoglobin in meat is converted to brown metmyoglobin

Maillard reaction
Loss of amino acids
Vitamin loss - thiamine, pantothenic acid

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6
Q

Fruit and Veg colour and taste

A

Green converted to olive green
Carotenoids are isomerized to less intense colour

Purple turn brown
Aroma and taste degrade
Loss of water soluble vitamins

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7
Q

Milk colour and taste

A

Maillard browning

Cooked flavour - denaturation of whey protein

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8
Q

Batch process

A

Portion of food is heated and then cooled

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9
Q

Continuous process

A

Food travels in and out

Better capacity

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10
Q

Different type of pasteurisations

A

Low temperature long time

High temperature short time

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11
Q

Low temperature long time examples

A

Cheese making

63 degrees for 60 minutes

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12
Q

HTST examples

A

Milk

71.7 degrees for 15 seconds

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13
Q

Ultra High temperature

A
UHT
Increase rate of killing microorganisms
Not proportional to other properties
So quick does not alter chemical and physical 
Creates shelf life of 6 months
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14
Q

UHT process

A

o 100 degrees achieved by heat exchange
o After this pump steam at a very high temperature – reaching 132 degrees
o Fluid cools steam to water
o Heats the food up
o Heating food turns water back to steam
o Only few seconds the temperature is reduced and the steam is removed
 Only recover 50% energy not as good as counter current system

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15
Q

Advantages of heat

A

Well established technology
Both solid and liquids
Known safety performance

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16
Q

Disadvantages of heat

A

Loss of taste and nutrients
UHT not energy efficient pasteurisation requires refrigeration
Loss of texture

17
Q

Non-thermal methods for reduction

A

Microfiltration
Pulsed electric fields
High pressure treatment

18
Q

Microfiltration

A

Removal of bacteria and spores by allowing liquid to pass through membrane but not microbes
<0.2 micro metre pore size
Pressure of 0.2-0.4 bar
3-4 log reduction

19
Q

Advantages of microfiltration

A

Permits lower temperatures for thermal pasteurisation
Maintains product quality and nutritive value
Significantly extends product shelf-life

20
Q

Disadvantages of microfiltration

A

Membrane life relatively short
Restricted to liquids
Thermal pasteurisation still required

21
Q

Pulsed electric field

A

Pumped liquid through electrode
In middle there is strong electric field which interferes with microbes
Causes pores in membrane leading to cell lysis

Effective Yeast> gram negative > gram positive ( the more complex the membrane the more susceptible)
Achieves 5-6 logs

22
Q

Advantages of pulsed electric field

A

Negligible heat generated
Retain sensory and nutritional quality
Continuous process

23
Q

disadvantages of pulsed electric field

A

Restricted to liquids
Hardware still being developed
Expensive

24
Q

High pressure treatment

A
Food subject to hydrostatic pressure 100-800MPa
Pressure acts immediately and uniformly throughout product
Any size and shape
Temp increase by 3 degrees 
Inactivation dependent on temperature
More efficient at elevated temperatures
Gram negative > gram positive > spores
Low pH better
25
High pressure treatment advantages
Effective at decreasing microbial populations Works for solid foods Minimal effect on quality Preserves nutritional content
26
Disadvantages of high pressure treatment
Batch process Expensive Can discolour food