High pressure processing Flashcards
What pressures are used?
100-1000 MPa
100 MPA = 1000 atmospheres
Describe process
Packages are submerged in a liquid - pressure applied, distributed instantaneously an uniformly, food is treated evenly
Le Chatelier’s Principle
When a system is subjected to a constraint, changes occur which seek to minimise that constraint
High pressure discourages:
Chemical reactions which produce volatiles
Phase changes that lead to expansion e.g. freezing of water, melting of fats
Principles in pressure processing:
- 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
Phase changes - lipids solidify at higher temperatures when under pressure
useful for rapid crystallisation of fat in spread manufacture
Phase changes - high pressure freezing causes less damage
- 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
Destruction causes less collateral damage
vs. heat inactivation as heat can damage proteins and vitamins
inactivation thought to be due to phase changes in lipid bilayer
Yeasts and moulds
are most sensitive
Gram negative more sensitive than
gram positive bacteria
Bacterial spores are less sensitive than
growing cells
- pulsed pressures used rather than static pressure
- ambient - 600 MPa - ambient - 600 MPa
- causes 10^6 fold decrease in Bacillus stearothermophilus
Bacteria are more sensitive at
lower pH
Macromolecules - pressures can force molecules into altered conformations occupying less space
- Alteration in hydrogen bonding and ionic bonding but covalent bonding unchanged
- Functional properties modified
Macromolecules - proteins
- 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
Benefits
- 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
Examples
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
