High pressure processing

Question 1

What pressures are used?

Answer 1

100-1000 MPa

100 MPA = 1000 atmospheres

Question 2

Describe process

Answer 2

Packages are submerged in a liquid - pressure applied, distributed instantaneously an uniformly, food is treated evenly

Question 3

Le Chatelier’s Principle

Answer 3

When a system is subjected to a constraint, changes occur which seek to minimise that constraint

Question 4

High pressure discourages:

Answer 4

Chemical reactions which produce volatiles

Phase changes that lead to expansion e.g. freezing of water, melting of fats

Question 5

Principles in pressure processing:

Answer 5

• any reaction which leads to a decrease in volume will be favoured or accelerated
• any reaction that involves an increase in volume will be inhibited
• electrostatic and hydrophobic interactions break easily
• hydrogen bonds are relatively inert to pressure
• covalent bonds are pressure stable

Question 6

Phase changes - lipids solidify at higher temperatures when under pressure

Answer 6

useful for rapid crystallisation of fat in spread manufacture

Question 7

Phase changes - high pressure freezing causes less damage

Answer 7

• freezing point of water is lower at higher pressures (can be liquid at -20 degrees C)
• store at lower temperatures without ice formation
• ice that does form has a higher density…..less expansion

Question 8

Destruction causes less collateral damage

Answer 8

vs. heat inactivation as heat can damage proteins and vitamins
inactivation thought to be due to phase changes in lipid bilayer

Question 9

Yeasts and moulds

Answer 9

are most sensitive

Question 10

Gram negative more sensitive than

Answer 10

gram positive bacteria

Question 11

Bacterial spores are less sensitive than

Answer 11

growing cells

• pulsed pressures used rather than static pressure
• ambient - 600 MPa - ambient - 600 MPa
• causes 10^6 fold decrease in Bacillus stearothermophilus

Question 12

Bacteria are more sensitive at

Answer 12

lower pH

Question 13

Macromolecules - pressures can force molecules into altered conformations occupying less space

Answer 13

• Alteration in hydrogen bonding and ionic bonding but covalent bonding unchanged
• Functional properties modified

Question 14

Macromolecules - proteins

Answer 14

• After pressure treatment a protein will refold to form a protein with an altered conformation - increased surface activity - improved foaming qualities
• Gels have different rheological properties - novel textures - acid-set gels are stronger and more viscous due to exposure of hydrophobic groups
• Some enzymes (lipases and proteinases) increase under perssure
• Starch will gelatinise at high pressure without heating - also retrogrades more slowly

Question 15

Benefits

Answer 15

• Pressure is transformed uniformly and instantaneously (compare with heat-processing- temperature gradient)
• Bacteria, yeast and moulds are sensitive to pressure - but normally little or no loss of colour, flavour and nutritionally quality
• Energy required for processing is minimal
• Little effluent produced
• But high cost of equipment

Question 16

Examples

Answer 16

Citrus juices - france - inactive pectin esterases
Japan - jams, fruit juice, sald dressings
Spain - cooked sliced ham - increases quality and shelf life
USA - Guacamole, oysters
Guacamole - 500 MPa for 20 mins - shelf life 4-6 weeks - inactivates PPO, bright green colour maintained
Oysters - easy to open shells - less labour intensive - improved microbial quality - improved yield - water absorbed during process