High-Pressure Processing (HPP): Principles, Equipment, Applications, and Food Industry Uses

Table of Contents

• Introduction to High-Pressure Processing (HPP)
• Principle of High-Pressure Processing (HPP)
• Equipment of High-Pressure Processing (HPP)
• Effect of High-pressure on Microorganisms
• Types of bacteria and HP processing conditions
• Working mechanism of High-Pressure Processing (HPP)
• Processing parameters
• Uses of High-Pressure Processing (HPP)
• Application of High-Pressure Processing (HPP) and some examples
• References

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Introduction to High-Pressure Processing (HPP)

• High-pressure processing (HPP) is a novel technology used for food preservation.
• In this process, food is subjected to pressure ranging between 40 and 1000 MPa for a specific duration.
• The treatment time can vary from milliseconds to several minutes, depending on the requirements.
• Processing takes place under controlled temperatures, which can range from below 0°C to above 100°C.
• The purpose of HPP is to achieve microbial inactivation or to alter food attributes in order to obtain desired food characteristics.
• For reference, 1 MPa equals 145.03 psi or 10 bar.
• This technology is also referred to as high hydrostatic pressure (HHP) or ultrahigh-pressure (UHP) processing.

Principle of High-Pressure Processing (HPP)

• High-pressure processing (HPP) is based on the Le Chatelier principle, which states: “Whenever pressure is applied to a system in equilibrium, the system will react to counteract the effect of constraint.”
• Under high pressure, such reactions result in a decrease in volume, leading to the inactivation of microorganisms and enzymes.
• Another fundamental principle of HPP is isostatic processing, which states: “When the food product is compressed by uniform pressure from every direction, it will return to its original shape when pressure is released.”
• Microorganisms, chemical reactions, biochemical and enzymatic processes, as well as the functional properties of biomolecules, are significantly affected by high pressure.

Equipment of High-Pressure Processing (HPP)

Two types of compression setups for HPP according to the pressure generation module:

Direct compression HPP

• Pressure is generated by moving a small diameter piston using hydraulic pressure, which reduces the volume.
• Allows fast compression.
• Requires a high-pressure dynamic seal between the piston and the internal vessel surface.
• Mostly applicable to laboratory or pilot plant systems.

Indirect compression HPP

• Uses a high-pressure intensifier to pump the desired pressure from a reservoir into a closed high-pressure vessel.
• Mostly applicable to commercial-scale operations.

Main components of high-pressure process systems include:

• A high-pressure vessel and its closure.
• Pressurizing system.
• Heating and cooling system.
• Materials handling system.
• Data generation system, including a microprocessor controller.
• Components of high-pressure process systems (collectively functioning together).

Effect of High-pressure on Microorganisms

• The sensitivity of microorganisms to high pressure varies depending on:
• The type of microorganism (food poisoning or food spoilage organisms).
• The form of the microorganism (vegetative form or spore form).
• Gram-positive bacteria are generally more resistant to high pressure than Gram-negative bacteria, mainly due to the presence of teichoic acid in their cell walls.
• Bacterial spores are significantly more resistant to pressure compared to vegetative cells because:
• Spores contain calcium-rich dipicolinic acid, which provides protection.
• This compound helps spores resist excessive ionization under high pressure.

Types of bacteria and HP processing conditions

• Vegetative form of bacteria: Inactivated at 400–600 MPa.
• Spore form of bacteria: Require more than 1000 MPa for inactivation.
• Staphylococcus: Inactivation achieved at more than 500 MPa for over 60 minutes.
• Escherichia coli: Shows a 6 log cycle reduction at 405 MPa for 10 minutes.
• Saccharomyces cerevisiae: Shows more than 6 log cycle reduction at 405 MPa for 10 minutes.
• Bacillus cereus spores: Require more than 800 MPa for inactivation.
• Vibrio parahaemolyticus: Achieves a 6 log reduction at 200 MPa for 20 minutes.
• Listeria monocytogenes: Inactivated at 340 MPa for 20 minutes.

Working mechanism of High-Pressure Processing (HPP)

Food type:

• The food product is packaged in a flexible container (such as a plastic pouch or bottle) and sealed.
• Ethylene-vinyl alcohol copolymer (EVOH) and polyvinyl alcohol (PVOH) are recommended materials for food packaging.
• The packaged food is then loaded into the high-pressure chamber, which is filled with a pressure-transmitting fluid for pressurization.
• Deaeration is carried out using a pump to remove trapped air.
• Pressure is then generated in the system using a pump and applied to the desired level for a specific time.
• After treatment, the product is removed from the setup and stored properly.

Processing parameters of HPP:

• The cost of operation depends on:
• Time of exposure
• Processing temperature
• Processing pressure
• The range of processing pressure varies with water activity and the type of food product.

• The processing temperature is selected based on the objective of treatment.
• Processing temperature applications:

• HP cold pasteurization (HP-LT): Aims to inactivate vegetative pathogenic bacteria.
• HP-assisted pasteurization and HP-assisted sterilization: Aimed at sterilizing low-acid foods and inactivating bacterial spores.
• The holding time in the pressure vessel depends on both the type of food matrix and the processing temperature.
• Optimization of HPP is directly related to the targeted pathogenic and spoilage bacteria.
• Operation modes of HPP:
• Can be carried out in batch mode or semi-continuous mode for commercial applications.
• In batch processing, prepacked foods are loaded into a processing vessel.
• In semi-continuous processing, pumpable products are used.
• Industrial HPP is most commonly carried out in batch processing mode.
• High-pressure processing system (based on orientation):
• Horizontal HPP system
• Vertical HPP system

Uses of High-Pressure Processing (HPP)

• Pathogen elimination – HPP effectively inactivates pathogenic microorganisms, making food products safer for consumption.
• Shelf-life extension – By reducing spoilage microorganisms, HPP extends the storage life of food without compromising quality.
• Innovative fresh products – Enables the development of new, minimally processed foods with fresh-like characteristics.
• Increased shellfish yields – Helps separate meat from shells more efficiently, resulting in higher yields for shellfish products.
• Reduced sodium products – Allows formulation of low-sodium foods while maintaining safety and quality.
• Clean-label products – Supports the production of preservative-free and additive-free foods that meet consumer demand for natural products.
• Convenience – Provides ready-to-eat, safe, and high-quality foods with minimal processing.

Application of High-Pressure Processing (HPP) and some examples

• Jams, fruit sauces, fruit jellies, yogurts
• Processed at 400 MPa, 20ºC, for 10–30 minutes
• Packaged in plastic cups
• Grapefruit juices
• Processed at 120–400 MPa, 20ºC, for 2–20 minutes
• Packaged in glass bottles
• Tropical fruits
• Processed at 50–200 MPa
• Packaged in paper cups
• Beef
• Processed at 100–250 MPa, 20ºC, for 30 minutes to several hours
• (Packaging not specified)
• Rice cake
• Processed at 400 MPa, 45–70ºC, for 10 minutes
• (Packaging not specified)

References

• Potter, N. P. (1987). Food Science. CBS Publishers, India.
• Rahman, M. S. (1999). Handbook of Food Preservation. Marcel Dekker, Inc., New York.
• Desrosier, E. N. (1963). The Technology of Food Preservation. AVI Publishing Company, New York.
• High Pressure Processing for the Food Sector. High Hydrostatic – Laboratory, R&D and Production Systems. Retrieved from highpressurefoodprocessor.com