Pasteurisation Flashcards
Heat Preservation
Destroy pathogens reduce and eliminate microbial Enzyme Activity Extend shelf life With minimal damage to nutrients and sensory components
Temperature Vegetative state die at
60 degrees
Spore state die at
Survive above 100 degrees
Heat effect on food
Colour and taste effects canned meat, fruit and veg and milk
Canned meat colour and taste
Oxymyoglobin in meat is converted to brown metmyoglobin
Maillard reaction
Loss of amino acids
Vitamin loss - thiamine, pantothenic acid
Fruit and Veg colour and taste
Green converted to olive green
Carotenoids are isomerized to less intense colour
Purple turn brown
Aroma and taste degrade
Loss of water soluble vitamins
Milk colour and taste
Maillard browning
Cooked flavour - denaturation of whey protein
Batch process
Portion of food is heated and then cooled
Continuous process
Food travels in and out
Better capacity
Different type of pasteurisations
Low temperature long time
High temperature short time
Low temperature long time examples
Cheese making
63 degrees for 60 minutes
HTST examples
Milk
71.7 degrees for 15 seconds
Ultra High temperature
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
UHT process
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
Advantages of heat
Well established technology
Both solid and liquids
Known safety performance
Disadvantages of heat
Loss of taste and nutrients
UHT not energy efficient pasteurisation requires refrigeration
Loss of texture
Non-thermal methods for reduction
Microfiltration
Pulsed electric fields
High pressure treatment
Microfiltration
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
Advantages of microfiltration
Permits lower temperatures for thermal pasteurisation
Maintains product quality and nutritive value
Significantly extends product shelf-life
Disadvantages of microfiltration
Membrane life relatively short
Restricted to liquids
Thermal pasteurisation still required
Pulsed electric field
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
Advantages of pulsed electric field
Negligible heat generated
Retain sensory and nutritional quality
Continuous process
disadvantages of pulsed electric field
Restricted to liquids
Hardware still being developed
Expensive
High pressure treatment
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
High pressure treatment advantages
Effective at decreasing microbial populations
Works for solid foods
Minimal effect on quality
Preserves nutritional content
Disadvantages of high pressure treatment
Batch process
Expensive
Can discolour food
