Food ultra-high pressure sterilization equipment non-thermal sterilization
High Pressure Processing (HPP) equipment is a type of non-thermal sterilization equipment that uses water as the pressure transmission medium. Its core principle involves placing sealed packaged food in an ultra-high pressure container, where hydrostatic pressure is uniformly transferred to the food's interior via the water medium. The pressure typically ranges from 100 MPa to 600 MPa. This pressure level is several times higher than the pressure at the bottom of the deepest ocean trench, capable of disrupting the cell membrane structure of microorganisms, denaturing key proteins, and inactivating enzymes, thereby effectively inactivating pathogenic and spoilage bacteria.
Compared to traditional heat sterilization methods (pasteurization, high-temperature cooking) that rely on heat transfer, the fundamental difference in HPP technology is that it does not introduce an external heat source during the sterilization process. The processing temperature is typically controlled between 5°C and 25°C, falling under the category of low-temperature cold sterilization. Because the pressure transmission is instantaneous and uniform, regardless of the food's size or shape, the pressure at all points within the food is essentially the same, and the sterilization effect is not limited by product size or packaging shape. This non-thermal processing characteristic allows for a greater degree of preservation of the food's heat-sensitive nutrients and natural flavor. II. Equipment Structure and Core Systems
High-Pressure Chamber: The core pressure-bearing component of the equipment, manufactured using high-strength stainless steel forgings combined with a prestressed wire-wound structure. The chamber design must meet fatigue life requirements under ultra-high pressure, typically withstanding over 100,000 pressurization cycles. Chamber sizes range from several liters for laboratory-grade systems to tens of liters for pilot-scale systems, and hundreds of liters for industrial-grade systems. Large industrial equipment can have chamber diameters exceeding 300mm and effective working lengths exceeding 3000mm.
Pressure Boosting System: Consists of a high-pressure pump, booster, and pressure control valve assembly. Low-pressure water is initially pressurized by the high-pressure pump, and then the booster amplifies the pressure to the target level. The configuration of dual boosters working in tandem improves pressurization efficiency, ensuring that the target pressure of 600MPa is reached within 2 to 5 minutes.
Temperature Control System: Although it is a non-thermal process, the water medium and food will experience a certain temperature rise during pressurization (approximately 3°C per 100MPa). The equipment uses a heat exchanger and water circulation system to control the medium temperature within a set range, ensuring the processing temperature meets process requirements.
Material Loading and Unloading System: Industrial equipment is typically equipped with loading baskets and automatic conveying devices to achieve batch loading and unloading of products. The design of the loading baskets must ensure that the water flow evenly surrounds each product, avoiding uneven local pressure transmission.
Control System: Utilizing a PLC programmable logic controller in conjunction with a touchscreen human-machine interface, key parameters such as pressure, holding time, and temperature can be set and monitored, and batch processing data can be recorded to meet food safety traceability requirements.
III. Core Technical Parameters
Working Pressure: The maximum working pressure of standard industrial equipment is 600 MPa, and some equipment can be adjusted within the range of 100 MPa to 600 MPa. For products where only shelf life needs to be extended, lower pressures can be used to reduce energy consumption and equipment wear.
Processing Temperature: Conventional HPP processing is carried out in the range of 5℃ to 25℃, which is considered room temperature to low temperature processing. Some special applications can be carried out below 80℃ to meet the specific process requirements of certain products.
Holding time: Determined based on product type and the pressure tolerance of the target microorganisms, typically 1 to 5 minutes. Spore-forming microorganisms require longer holding times or higher pressure levels.
Circulation efficiency: A complete cycle for a single batch includes five stages: loading, pressurization, holding, depressurization, and unloading, with a total time of approximately 6 to 12 minutes. Pressurizing to 600 MPa takes approximately 2 to 5 minutes, while depressurization is instantaneous.
Sterilization effect: Effectively kills common foodborne pathogens such as Listeria, Salmonella, Escherichia coli, and Vibrio, as well as spoilage microorganisms such as yeasts and molds. Its inactivation effect on bacterial spores is limited; therefore, treated products require cold chain storage.
IV. Process Adaptation for Multiple Food Categories
Fruit juices and beverages: The earliest commercially viable application of HPP technology. Cold-pressed fruit juices treated with HPP effectively kill spoilage microorganisms and pathogens, while avoiding flavor degradation and nutrient loss caused by heat sterilization. The retention rates of Vitamin C, anthocyanins, and polyphenols are significantly higher than with heat sterilization processes. Under cold chain conditions of 0°C to 4°C, the product's shelf life can reach 30 to 90 days.
Meat products and ready-to-eat meats: including sliced ham, ready-to-eat chicken breast, and braised cooked foods. HPP effectively inactivates pathogenic bacteria such as Listeria without altering the tenderness and juiciness of the meat products. The shelf life of processed ready-to-eat meats under cold chain conditions can be extended from several weeks to several months. HPP can also be used in meat processing to improve the uniformity of salt distribution, reducing sodium content without affecting the perceived saltiness.
Seafood and shellfish: HPP has unique advantages in seafood processing. For shellfish products, pressure allows the meat to automatically separate from the shell, achieving a high meat yield and eliminating the need for manual shelling or steaming. Simultaneously, this technology effectively inactivates marine pathogenic bacteria such as Vibrio, maintaining the fresh, sweet flavor and elastic texture of seafood. It is suitable for ready-to-eat shrimp, crab meat, smoked salmon, and other products. Pre-prepared and ready-to-eat foods: Suitable for prepared foods that require retaining the freshly made texture, including Chinese dishes, soups, sauces, and ready-to-eat salads. HPP treatment slows down enzymatic browning, maintaining the crispness and natural color of vegetables without the need for chemical color-protecting agents. The product has a shelf life of 30 to 90 days under cold chain conditions.
Application Boundaries: HPP technology is highly effective for products with high water activity. For products with low water activity (such as dried seasonings, dehydrated vegetables, nuts, and baked goods), the sterilization effect is limited due to the lack of sufficient free water as a pressure transmission medium. Completely frozen products are also unsuitable for conventional HPP treatment and must be thawed to a suitable temperature first. Furthermore, the product packaging must be flexible and airtight, capable of withstanding approximately 15% volume compression without breaking.
