Jamie Valenti-Jordan is Food Brand Program Manager at the Food Finance Institute.
At its core, high pressure processing (HPP) leverages the principle of isostatic pressure, where pressure is transmitted uniformly and instantaneously throughout a liquid medium. This hydrostatic pressure, typically ranging from 400 to 600 MPa, induces non-covalent bond disruptions within biological molecules. Specifically, microbial inactivation occurs through the denaturation of proteins essential for cellular function and the disruption of cell membranes. This pressure-induced inactivation is largely independent of product geometry, allowing for uniform treatment of complex food matrices.
The process involves placing packaged food within a pressure vessel filled with water. The pressure is then rapidly increased and held for a specific dwell time, typically ranging from a few seconds to several minutes, before being released. This pressure application leads to a volumetric compression of the food, typically around 15%, which causes proteins to unfold to a pressure-induced, high potential energy state. This protein, when pressure is released, does not have the traditional cellular enzymes as guides to refold the protein to its intended state and thus can find a new tertiary structure that has (typically) an inert activity—if this new native-folding structure were not inert, then cellular enzymes to guide this folding likely would not have evolved and been energetically favorable to produce.
The primary mechanism of microbial inactivation in HPP is the disruption of microbial cell membranes. This disruption causes leakage of cellular contents and ultimately leads to cell death. Secondarily, the impact of high pressure on the folding mechanisms of proteins means that metabolic activity and spoilage are reduced by denaturing enzymes themselves. Unlike thermal processing, which relies on heat transfer and can lead to significant degradation of heat-sensitive compounds, HPP minimizes changes in the food's chemical composition, preserving vitamins, pigments, and flavor compounds. The effect of HPP on enzymes is dependent on the enzyme type; some enzymes are highly pressure sensitive. Ideally, the specific pressure and dwell time are optimized based on the target microorganisms and the specific food matrix to achieve the desired level of microbial inactivation and enzyme control while maintaining product quality, but in practice, a standardized program is often run by processors.
Interesting food applications
The versatility of HPP has led to its adoption across a wide range of food categories. In ready-to-eat (RTE) meats and poultry, HPP effectively eliminates Listeria monocytogenes and other pathogens, providing a critical safety barrier, particularly valuable for products like deli meats, sausages, and poultry. For juices and beverages, HPP allows for the production of "cold-pressed" juices with extended shelf life without compromising their natural flavors and vitamin content—appealing to consumers drawn to minimally processed, nutrient-rich beverages. In avocado products, HPP prevents enzymatic browning and maintains the vibrant green color and creamy texture of guacamole and avocado pulp, significantly extending their shelf life. As highlighted in the February issue, Lilián Robayo reported that RV Fresh Foods has expanded its operations with the installation of HPP equipment in the avocado industry. For seafood, HPP enables the shucking of shellfish without heat, resulting in higher yields and improved texture while also effectively eliminating Vibrio species, enhancing seafood safety. Finally, HPP maintains the crispness and freshness of fruits and vegetables, extending shelf life and reducing waste. Jim Jindra, VP of R&D at Catapult Commercialization Services, stated, "HPP has been a game-changer for food safety, particularly in the RTE meat sector. The ability to eliminate listeria without heat is invaluable. However, ongoing research is crucial to optimize process parameters for different food matrices."
HPP pathogens to provide a safety barrier for products like deli meats, sausages, and poultry.Image courtesy of ltyuan/Adobe Stock
Technical limitations
While HPP offers numerous advantages, it's not without its limitations. The initial investment in HPP equipment is substantial, limiting its accessibility for smaller processors, which leads to the common practice of small and medium-sized companies utilizing tolling contract processors. Tolling allows businesses to access HPP technology without the significant capital expenditure of purchasing their own machines. This model enables them to offer HPP-treated products while mitigating the financial barriers associated with equipment ownership.
Products with high air content or delicate structures are not suitable for HPP, as certain products, such as whole fruits and vegetables with intact air pockets, are crushed or deformed under high pressure. HPP requires flexible packaging that can withstand high pressure without rupturing; rigid packaging, such as glass or metal cans, is generally not compatible because they resist the translation of the pressure, and as such, they become brittle under pressure.
Effective packaging solutions include flexible or semi-rigid materials like plastic cups and pouches, designed to maintain product integrity under extreme pressure, emphasizing that selecting the appropriate packaging is critical to prevent leaks and ensure product safety. Jessica Schwartz, Packaging Engineer, notes, "The evolution of flexible packaging has been pivotal for HPP's success. Innovations in high-pressure-resistant films and pouches enhance product protection and presentation. However, ensuring package integrity under extreme pressure remains a critical area of focus."
The future of HPP innovation and expansion
Matt Tom, Commercialization Expert, explains, "HPP has allowed the creation of products that were previously impossible. The ability to offer fresh-like juices and guacamole with extended shelf life has been a major competitive advantage. However, understanding the specific pressure and time requirements for each product composition is essential to achieve optimal results. As HPP technology advances, such as in combination with thermal cycling, the range of products and microorganisms that can be reliably treated really opens up. Finally, HPP really levels the playing field by enabling smaller companies to leverage this technology via tolling, eliminating the daunting capital expense."
As technology advances and costs decrease, HPP is poised for even greater adoption in the food industry. Ongoing research is exploring new applications, such as the processing of powders and dry ingredients. The development of more efficient and cost-effective HPP equipment will further democratize this technology, making it accessible to a wider range of processors. RV Fresh Foods also plans to diversify its product portfolio by introducing new variants of avocado-based sauces, purees, and value-added products such as healthy snacks and dips. This offering expansion is in response to the trend of consuming healthy and convenient foods.
In conclusion, HPP represents a significant leap forward in food processing, offering a safe and effective method for preserving freshness and extending shelf life. The adoption of HPP technology has allowed companies like RV Fresh Foods to improve the quality of their products, extend their shelf life, and reduce their environmental impact. While technical limitations exist, continuous innovation and research are paving the way for a future where HPP plays an even more prominent role in delivering high-quality, safe, and nutritious food to consumers.
