Hydrostatic pressure processing involves the use of high water pressure in a special pressure vessel to kill the bacteria but preserve texture, nutrients, and color of food.
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2. Presentation Outline
Introduction
HPP and how it works
Factors affecting HPP effectiveness
Effects on chemical and microbiological properties of food
Application
Limitations
Conclusion
3. What is Hydrostatic Pressure Processing?
Non-thermal food processing technique that relies
on very high hydrostatic pressure (up to 1000MPa)
using a specially designed pressure vessel to obtain
microbiologically safe food products with extended
shelf life and minimal effect on physico-chemical,
sensory, and nutritional aspects of the food.
Other names:
• High hydrostatic pressure processing
• Ultra high pressure processing
• Pascalization
• Cold pasteurisation
4. The Working Principle (1)
Great risk: recontamination of ready to eat foods just
before packaging.
Hydrostatic Pressure Processing (HPP) is employed
after packaging to minimize the risk.
HPP relies on instantaneous and uniform
transmission (isostatic) of pressure throughout the
food independent of its size or shape.
Food is not crushed since Le Chatelier’s principle
must hold true.
5. The Working Principle (2)
Pressure disrupts cell morphology, membranes, spore
coats, and denatures proteins.
Disrupted membranes lead to increased permeability
causing leakage of cell protoplasm.
Pressure acts on hydrophobic and ionic bonds as
opposed to heat treatment (acts on covalent bonds).
Adiabatic heating: every 100MPa causes 3°C-6°C
increase depending on the food components. The
additive effect may alter foods.
7. Factors Aiding Effectiveness of HPP
pH: Low pH enhances the effect of HPP on microorganism
Temperature: Adiabatic increase in temperature due to
increase in pressure
Water activity: Sub-lethally injured bacteria rovers fast when
there’s high levels of water activity
Preservatives: Adding lactate reduces initial microbial
inactivation but also delays later recovery
Bacteriocins (e.g. Nicin) become more effective under high
pressure even on gram negative bacteria.
8. Effects of Pressure on Chemical Properties
of Food
Disruption of hydrophobic and ionic bonds does not affect
texture much (unlike heat, which breaks covalent bonds and
modifies texture).
Thickening of starchy foods and gels have increased
viscosity.
About 7% of ascorbic acid lost in the process (comparable to
loss during storage: not significant) Bull et al., (2005).
No effect on β-carotene
Reversible crystallization of lipids
9. Effects on Microbiological Properties of
Food
Pressure of between 400-600MPa/≤2 minutes: reduce
vegetative bacteria by ≤4 log cycles.
Microbial resistance is greatly variable.
• Gram positive bacteria (e.g. Listeria monocytogenes) have higher
resistance than gram negative bacteria (e.g. Salmonella).
Spores and viruses have large variations of pressure
resistances.
Effectiveness of HPP depends on:
Amount of pressure applied and holding time,
Food matrix and temperature
Target microorganism
10. HPP Table for 5 Log Reduction of
Salmonella in Orange Juice
Pressure (MPa) Holding Time (seconds)
300 369
350 136
400 55
450 25
500 13
Bull et al., (2005).
11. Why HPP?
The dilemma:
Destroying pathogenic microorganisms
versus preserving flavor, texture, color, and
nutritional quality of food.
Improving food safety and extending the shelf
life. Reduces the load of spoilage
microorganisms.
Elimination of recontamination of processed
food.
12. Why HPP? (2)
Avoiding use of chemical preservatives. Clean label
foods.
Preserving food quality (flavor, texture, color, and
nutrition). Resulting food has excellent organoleptic
quality.
Some pressure levels have been shown to increase
antioxidant levels (Tewari et al., 2016).
Better quality products after reformulation.
13. Advantages
Applicable to foods where heating could be
detrimental (e.g. ready to eat foods like guacamole).
Minimal interference with organoleptic quality of the
food.
Cheap: uses tap water and electricity
Environmentally friendly: no harmful byproducts
Provides a safer working environment for
employees.
14. Limitations of HPP
Some bacterial spores may require more than just
high pressure to inactivate.
More suitable for acidic foods because the acid will
suppress vegetating spores after HPP treatment.
Some food enzymes (baro-resistant enzymes e.g.
PME) are resistant to high pressure treatment: will
still cause food spoilage.
Structure starchy and high protein foods are altered
under high pressure treatment.
15. Obstacles to implementation of HPP
Government agencies do not have positive attitude
towards HPP. Low levels of support.
Low levels of public awareness.
Fewer suppliers of processing equipment.
High initial cost: need to purchase multiple
components simultaneously.
Fear of economic risks: newer versions usually get
obsolete fast.
16. Conclusion
HPP promises to eliminate post processing
recontamination since food is processed after
packaging.
Using hot water in the HPP system will inactivate the
most resistant spores (Jayachandran, Chakraborty and
Rao, 2016).
Characteristics of the packaging material used:
Water resistant
Flexible enough to re-adjust after pressure treatment (15-18%)
Polythene and polyethylene materials are preferred due to their thermosealability and barrier properties
Critical in ready to eat foods e.g. guacamoles.
Some gram positive bacteria such as Listeria monocytogenes can exhibit higher resistance than gram negative bacteria such as Salmonella.
No byproducts like new chemical compounds and radiolytic byproducts.
Pectin methylesterase (PME) – needs pressure/heat combination to inactivate.