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. You can read more about pasteurization here https://agritimps.com/milk-pasteurization-101

1. Hydrostatic Pressure
Processing: The Next Frontier
in Fruit Processing
Kevine O. Otieno

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.

6. HPP Process Illustration
Source: Avure, (2014).

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).

17. Thank You