Unlocking the Potential of High Hydrostatic Pressure: A Fresh Approach to Food Preservation

In an age where consumers are increasingly conscious of what they eat, the demand for natural, minimally processed, and chemical preservative-free products has significantly increased. Unlike traditional thermal methods, high hydrostatic pressure (HHP) is a non-thermal food processing technology that uses pressure instead of heat to inactivate microorganisms and enzymes, protecting the heat-sensitive food constituents (vitamins, minerals, and nutrients). Consequently, a safe, high-nutrition, and quality food product can be achieved with HHP (1). Compared to other non-thermal technologies such as Pulsed Electric Fields, Ultrasound, and Non-thermal Plasma, HHP has already been scaled up and is used by food manufacturers. However, the adoption and market penetration of HHP remains limited, primarily due to several challenges, with high operational costs being the most significant.

Key Challenges in Implementing High Hydrostatic Pressure (HHP) Technology

• Limited Effectiveness Against Spores: Although HHP is effective against a wide range of pathogens, it cannot completely inactivate all spore-forming bacteria unless combined with other treatments or at higher pressures. Studies have shown that a combination of pressure and temperature (>100oC) is required to inactivate Bacillus stearothermophilus spores in egg patties (10).
• Reduced Effectiveness on Low-Moisture Foods: HHP’s effectiveness in inactivating microbes can be reduced in foods with low water activity. To ensure optimal results, it is recommended that products have a water activity (Aw) level greater than 0.8 (1,4).
• Potential Impact on Texture or Colour: HHP under intense pressures (>500 MPa) can alter the texture of meat, fish, and poultry products due to changes in the structure of macromolecules like proteins during the process. Additionally, it may lead to changes in color due to modifications in pigment molecules such as myoglobin. However, these alterations typically do not affect the nutritional composition or flavor (2).
• High Operational Costs: HHP machinery and pressure vessels are expensive to purchase and install, which can be a significant barrier for small and medium-sized food producers. Furthermore, although HHP does not require heat, it consumes a considerable amount of energy to generate the pressures needed for effective processing. 

All the above leads to higher prices for the end products, which may affect consumer acceptance and demand.

These challenges highlight the need for ongoing research and innovation to make HHP more accessible and efficient for widespread use in the food industry. Consequently, novel methods to reduce the pressure intensity, thereby lowering costs and expanding the product portfolio, are being investigated under the TRANSIT ITN research project. This could be achieved by applying hurdles that could enhance the antimicrobial properties of HHP, such as combining it with natural preservatives or mild heat treatments. By exploring these synergistic approaches, TRANSIT aims to develop more cost-effective and versatile HHP applications, ultimately benefiting both producers and consumers.

Hurdle Technology: Combining HHP with Antimicrobial Factors Natural Antimicrobials

The concept of hurdle technology in food preservation has been extensively studied combining multiple methods such as pH control, temperature, and packaging techniques to create synergistic barriers against microbial growth, thereby extending the shelf life of food products. By combining HHP with novel packaging solutions such as modified atmosphere packaging or active packaging systems, further inhibition of microbial growth and oxidative reactions is achieved, enhancing the overall effectiveness of the preservation process. For example, strawberries packaged in Modified Atmosphere Packaging (MAP) trays with reduced oxygen levels and subjected to HPP, demonstrated an extended shelf life by inhibiting spoilage microorganisms and enzymes responsible for deterioration. Additionally, recent research has shown applying low-intensity HHP (300 MPa) to vacuum-sealed chilled pork meat decreases the total mesophilic bacteria count and moisture content, thereby extending the shelf life (11).

Recently, combining low-intensity HHP treatment with natural antimicrobials for “clean label” products has emerged as one of the big trends. This approach creates a synergistic effect, enhancing microbial inactivation, lowering operational costs, and still preserving food quality.

Synergistic Effects with Natural Antimicrobials – The benefits of this combination

Exploring the synergistic effects of natural antimicrobials in combination with HHP presents an innovative approach to enhancing food preservation and safety. A few examples are listed below:

• Lysozyme, an enzyme found in egg whites, has demonstrated antimicrobial properties that complement the microbial inactivation achieved by HHP. For instance, using lysozyme with HHP showed promising results in milk and banana juices, effectively inactivating Escherichia coli and Salmonella spp. (8).
• Chitosan, a natural antimicrobial derived from crustacean shells and well-known for its antimicrobial properties, can synergistically enhance the microbial inactivation achieved by HHP. A recent study showed that HHP combined with chitosan exerts synergistic action against L. monocytogenes and E. coli on a laboratory scale, enhancing the possibility of application in food products (6) 
• Organic Acids such as citric or lactic acid, lower the pH of the food environment, which can disrupt bacterial metabolic processes. At the same time, HHP increases the permeability of bacterial cell membranes, making them more susceptible to the antimicrobial action of the organic acids. Minimally processed, safe tomato products (such as tomato puree) can be produced when a low intensity of HHP is used (400 MPa) with up to 2% w/w of citric acid (9).
• Pediocin is an antimicrobial peptide produced by Pediococcus acidilactici, known for its effectiveness against a broad range of pathogens, particularly Listeria monocytogenes. It is highly effective at low concentrations and specifically targets pathogenic bacteria without affecting beneficial microflora. For example, subjecting deli meats to HHP (400 MPa) combined with pediocin can achieve a significant reduction of L. monocytogenes. Additionally, good results have been shown when combining pediocin and HHP (300 MPa) in milk (7).
• Nisin is a natural preservative produced by Lactococcus lactis. A research study illustrated that combining high pressure and nisin in skim milk resulted in a greater inactivation of gram-positive bacteria than when either was applied individually (3). This combination has also been shown to be particularly effective in extending the shelf life of meat products and canned foods, where the synergistic action of nisin and HHP helps to control microbial spoilage and ensure product safety.
• Essential oils extracted from plants have antimicrobial properties that can be used in food preservation. Food producers can achieve prolonged shelf life while maintaining freshness and safety by applying HHP combined with essential oils like oregano, thyme, or cinnamon. The combination of HPP with lemon balm was studied in the USA and Taiwan, showing very promising results in effectively reducing E. coli in ground beef (5).

Conclusion

High Hydrostatic Pressure is a promising non-thermal food processing technology that preserves food quality while ensuring safety and aligning with the increasing consumer demand for natural and minimally processed foods. Its ability to maintain the nutritional and sensory characteristics of food while extending shelf life and enhancing safety makes it a valuable tool for food manufacturers. Despite its benefits, challenges such as high operational costs and potential impacts on texture and color must be addressed to broaden its product portfolio and its adoption by manufacturers.

By exploring synergistic approaches that combine HHP with natural antimicrobials and other preservation methods, the food industry can overcome these challenges and unlock new possibilities. Research initiatives like the TRANSIT ITN project are leading the way to more cost-effective and versatile HHP applications that can benefit producers and consumers. As technology advances and becomes more accessible, HHP is set to play a crucial role in the future of food processing, ensuring safer, higher-quality products for the global market.

References

1. Aganovic, K., Hertel, C., Vogel, R. F., Johne, R., Schlüter, O., Schwarzenbolz, U., … & Heinz, V. (2021). Aspects of high hydrostatic pressure food processing: Perspectives on technology and food safety. Comprehensive Reviews in Food Science and Food Safety, 20(4), 3225-3266.
2. Bak, K. H., Bolumar, T., Karlsson, A. H., Lindahl, G., & Orlien, V. (2019). Effect of high-pressure treatment on the color of fresh and processed meats: A review. Critical reviews in food science and nutrition, 59(2), 228-252.
3. Black, E. P., Kelly, A. L., & Fitzgerald, G. F. (2005). The combined effect of high pressure and nisin on inactivation of microorganisms in milk. Innovative Food Science & Emerging Technologies, 6(3), 286-292.
4. Bover-Cid, S., Belletti, N., Aymerich, T., & Garriga, M. (2017). Modelling the impact of water activity and fat content of dry-cured ham on the reduction of Salmonella enterica by high pressure processing. Meat science, 123, 120-125.
5. Chien, S. Y., Sheen, S., Sommers, C., & Sheen, L. Y. (2019). Combination effect of high-pressure processing and essential oil (Melissa officinalis extracts) or their constituents for the inactivation of Escherichia coli in ground beef. Food and Bioprocess Technology, 12, 359-370.
6. Giannoulis, N., & Karatzas, K. A. G. (2024). The combined effect of chitosan and High Hydrostatic Pressure (HHP) on Listeria monocytogenes and Escherichia coli. Innovative Food Science & Emerging Technologies, 103693.
7. Komora, N., Maciel, C., Pinto, C. A., Ferreira, V., Brandão, T. R., Saraiva, J. M., … & Teixeira, P. (2020). Non-thermal approach to Listeria monocytogenes inactivation in milk: The combined effect of high pressure, pediocin PA-1 and bacteriophage P100. Food microbiology, 86, 103315
8. Nakimbugwe, D., Masschalck, B., Anim, G., & Michiels, C. W. (2006). Inactivation of gram-negative bacteria in milk and banana juice by hen egg white and lambda lysozyme under high hydrostatic pressure. International journal of food microbiology, 112(1), 19-25.
9. Plaza, L., Muñoz, M., de Ancos, B., & Cano, M. P. (2003). Effect of combined treatments of high-pressure, citric acid and sodium chloride on quality parameters of tomato puree. European Food Research and Technology, 216, 514-519
10. Rajan, S., Pandrangi, S., Balasubramaniam, V. M., & Yousef, A. E. (2006). Inactivation of Bacillus stearothermophilus spores in egg patties by pressure-assisted thermal processing. LWT-Food Science and Technology, 39(8), 844-851.
11. Roobab, U., Shabbir, M. A., Khan, A. W., Arshad, R. N., Bekhit, A. E. D., Zeng, X. A., … & Aadil, R. M. (2021). High-pressure treatments for better quality clean-label juices and beverages: Overview and advances. Lwt, 149, 111828.

Further Reading

Harnessing pulsed power to enhance food safety and quality: Risks and benefits of pulsed electric field (PEF) technology.

Non-thermal plasma (NTP) for the improvement of food safety and quality

The Impact of Strain Variability on the Inactivation Efficacy of Ultrasound Technology

Exploring Pulsed Electric Field (PEF) Microbial Inactivation for Food Processing

Manothermosonication: Revolutionizing Liquid Whole Egg Pasteurization with Enhanced Safety and Quality

Understanding Consumer Perception in Food Product Development: Key to Market Success

Using AI to evaluate non-thermal processing efficacy and assess the global impact

Safeguarding Your Plate: How High-Pressure Processing Enhances Food Safety and Quality