Non-thermal pasteurisation techniques

Question 1

Microfiltration

Answer 1

Removal of bacteria and spores by passing liquid through a membrane with very small holes

Question 2

Micro filtration Advantages

Answer 2

• permits lower temp for thermal pasteurisation
• maintains products quality and nutritive value
• significantly extends products shelf-life

Question 3

Microfiltration disadvantages

Answer 3

• membrane life relatively short
• restricted to liquid
• thermal pasteurisation still required
• expensive

Question 4

Pulsed electric field

Answer 4

High intensity electric pulses are passed through liquid foods
Treatment times typically below 1 second
High susceptibility = low survival
Yeasts > Gram negative > Gram positive > Spores
Complex membranes increase susceptibility
Thick cell walls increase resistance and survival
Treatment can reduce levels of vegetative cells by 5-6 logs
Can be used in milk, fruit juices, soup, egg
Cell membranes are polarized in external field
Holes appear in membrane when a critical limit is surpassed (electroporation)

Question 5

Pulsed electric field Advantages

Answer 5

• Negligible heat generated
• retain sensory and nutritional quality
• continuous process

Question 6

Pulsed electric field advantages

Answer 6

• restricted to lipids
• hardware still being developed
• more inactivation data required
• expensive

Question 7

High pressure processing

Answer 7

• Food subject to high hydrostatic pressure (100-800 MPa for 1 second – 30 mins)
• Pressure acts instantaneously and uniformly throughout the product

-Independent of size, shape and food composition
As pressure is applied, temperature increases (3oC per 100 MPa)

• Inactivation dependent on temperature. Efficacy enhanced at elevated temperatures (45-50oC)
• Pressure (500-700 MPa) in combination with elevated temperatures (90-100oC) inactivate spores of Clostridium botulinum
• Batch process is performed in a sealed chamber
• Can be semi-continuous when using relatively low pressures
• Used in combination with temperature and anti-microbial agents

Question 8

High pressure processing - microbial resistance

Answer 8

Order of susceptibility:
Gram Negative> Gram Positive > Spores
Large differences in resistance across species
Low pH enhances lethal effect of pressure
Low aw decreases lethal effect of pressure

Question 9

High pressure processing - mode of inactivation

Answer 9

Still unknown but thought to involve shear forces generated
Membrane disruption
Localized thermal damage
Protein deformation

Question 10

Foods treated with high pressure processing

Answer 10

fruit juice, jam, yoghurt, meat, seafood

Question 11

High pressure processing - advantages

Answer 11

• effective at decreasing microbial populations
• minimal effects on product quality
• preserves nutritional content of food

Question 12

High pressure processing - disadvantages

Answer 12

• Batch process not complementary to high capacity lines
• expensive
• high pressures can discolour certain foods