High-pressure processing (HPP) is an innovative food preservation technique that uses high levels of pressure to inactivate harmful microorganisms, extending shelf life while maintaining the nutritional and sensory qualities of food. As a non-thermal process, HPP ensures that the food's natural properties remain largely unaffected, making it an increasingly popular choice in the food industry. It is often used for niche products, particularly those that benefit from minimal processing while retaining natural qualities, such as cold-pressed juices, baby food, ready-to-eat meals and premium deli meats. HPP is particularly appealing to companies marketing health-conscious and minimally processed food items, as it extends shelf life without compromising the food's sensory or nutritional attributes. This method is popular in sectors aiming to balance safety with the demand for "clean label" products.

An important factor in the effectiveness of HPP is the packaging. Proper packaging not only ensures the integrity and safety of food during and after HPP but also plays a pivotal role in maintaining the quality of the product throughout its shelf life. The selection of appropriate packaging materials is essential to protect the food from contamination and to withstand the intense pressure applied during processing.

Cold pressed juice that often uses HPP to extend shelf life. Source: Mike Mozart/CC BY 2.0

Overview of HPP

HPP is a non-thermal food preservation method that uses extreme pressure, typically ranging from 100 to 600 megapascals (MPa), to inactivate microorganisms and pathogens in food. During the HPP process, food products are sealed in flexible packaging and subjected to uniform pressure in all directions, without the use of heat. The process duration can vary depending on the food type and desired outcome but usually lasts from a few seconds to several minutes. The pressure disrupts the cellular structure of harmful microorganisms, ensuring food safety while maintaining product quality.

One of the primary benefits of HPP is its ability to significantly extend the shelf life of food products without altering their taste, texture or nutritional content. Unlike traditional heat-based preservation methods, HPP preserves the natural flavor and nutrients, making it an attractive option for consumers seeking minimally processed foods. Additionally, HPP effectively eliminates foodborne pathogens, ensuring that products remain safe for consumption over an extended period.

However, the success of HPP heavily depends on the selection of appropriate packaging materials. Packaging must be able to withstand the intense pressure without compromising its integrity or allowing contamination to occur. Inadequate packaging can lead to product damage, leakage or microbial contamination during or after processing, making it a critical component of the HPP system.

Characteristics of packaging materials for HPP

Packaging materials for HPP must have key properties: high mechanical strength to withstand pressures of 300 MPa to 600 MPa, excellent barrier properties to prevent contamination and chemical stability to avoid reactions with food. Flexibility and elasticity are also essential to accommodate pressure changes without compromising the seal. These characteristics ensure the packaging maintains food safety and quality during and after processing.

Materials commonly used in HPP packaging

Baby food pouches that undergo HPP. Source: Once Upon a Farm

Several materials have proven to be effective in HPP packaging applications. Polyethylene (PE) and its derivatives are among the most widely used due to their flexibility, cost-effectiveness and ability to endure high-pressure conditions. PE is particularly suitable for modified atmosphere packaging (MAP), where it helps extend the shelf life of various food products by providing a protective barrier. Another commonly used material is polypropylene (PP), which is valued for its high resistance to stress and its chemical inertness. While PP performs well under high-pressure conditions, certain food types present challenges that recent studies have explored, revealing both the strengths and limitations of PP in HPP applications.

Ethylene vinyl alcohol (EVOH) is another material frequently used in HPP, primarily because of its excellent gas barrier properties. This makes EVOH ideal for multilayer packaging structures where it protects products sensitive to oxygen and moisture. Polyethylene terephthalate (PET) is also popular for HPP packaging, offering a combination of transparency, mechanical strength and durability. Studies have demonstrated that PET performs reliably during HPP, maintaining its integrity and interacting minimally with the food.

Lastly, biodegradable materials such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA) are garnering attention due to growing environmental concerns. Recent research has explored the feasibility of using these biodegradable options in HPP, assessing their ability to withstand high pressure while offering a more sustainable packaging alternative. While these materials show promise, further studies are needed to evaluate their broader applicability in HPP environments.

Safety concerns and chemical migration

One key safety concern in HPP is the potential for chemical migration from packaging materials into food under extreme pressure. Research has shown that plasticizers, additives and other compounds used in traditional packaging materials can migrate into food, raising concerns about food safety. These risks highlight the importance of selecting packaging materials that are chemically stable under high-pressure conditions. In response to these concerns, new research is focusing on developing non-toxic alternatives that maintain safety and effectiveness in HPP environments. Additionally, regulatory bodies such as the FDA (U.S. Food and Drug Administration) and EFSA (European Food Safety Authority) have established global food safety standards that address packaging materials used in HPP. These standards require strict compliance to ensure that packaging materials do not pose a risk to consumers, further emphasizing the need for safe, compliant packaging solutions.

Innovations and future trends

Recent innovations in packaging for high-pressure processing include the development of nanocomposite materials. These materials offer enhanced barrier properties and improved mechanical strength, making them more resilient under the extreme pressures of HPP. Studies have shown promising results in the performance of nanocomposites, suggesting they may play a significant role in the future of HPP packaging. Alongside these advancements, there is a growing push toward sustainable packaging solutions, including biodegradable and renewable materials. Researchers are exploring the lifecycle impact of these materials in HPP environments, aiming to provide greener alternatives without compromising safety or effectiveness. The increasing focus on sustainability in packaging reflects broader industry trends, as consumers and regulatory bodies alike demand more eco-friendly options.