Pasteurisation

Question 1

Heat Preservation

Answer 1

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

Question 2

Temperature Vegetative state die at

Answer 2

60 degrees

Question 3

Spore state die at

Answer 3

Survive above 100 degrees

Question 4

Heat effect on food

Answer 4

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

Question 5

Canned meat colour and taste

Answer 5

Oxymyoglobin in meat is converted to brown metmyoglobin

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

Question 6

Fruit and Veg colour and taste

Answer 6

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

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

Question 7

Milk colour and taste

Answer 7

Maillard browning

Cooked flavour - denaturation of whey protein

Question 8

Batch process

Answer 8

Portion of food is heated and then cooled

Question 9

Continuous process

Answer 9

Food travels in and out

Better capacity

Question 10

Different type of pasteurisations

Answer 10

Low temperature long time

High temperature short time

Question 11

Low temperature long time examples

Answer 11

Cheese making

63 degrees for 60 minutes

Question 12

HTST examples

Answer 12

Milk

71.7 degrees for 15 seconds

Question 13

Ultra High temperature

Answer 13

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

Question 14

UHT process

Answer 14

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

Question 15

Advantages of heat

Answer 15

Well established technology
Both solid and liquids
Known safety performance

Question 16

Disadvantages of heat

Answer 16

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

Question 17

Non-thermal methods for reduction

Answer 17

Microfiltration
Pulsed electric fields
High pressure treatment

Question 18

Microfiltration

Answer 18

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

Question 19

Advantages of microfiltration

Answer 19

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

Question 20

Disadvantages of microfiltration

Answer 20

Membrane life relatively short
Restricted to liquids
Thermal pasteurisation still required

Question 21

Pulsed electric field

Answer 21

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

Question 22

Advantages of pulsed electric field

Answer 22

Negligible heat generated
Retain sensory and nutritional quality
Continuous process

Question 23

disadvantages of pulsed electric field

Answer 23

Restricted to liquids
Hardware still being developed
Expensive

Question 24

High pressure treatment

Answer 24

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

Question 25

High pressure treatment advantages

Answer 25

Effective at decreasing microbial populations
Works for solid foods
Minimal effect on quality
Preserves nutritional content

Question 26

Disadvantages of high pressure treatment

Answer 26

Batch process
Expensive
Can discolour food