Introduction
High-pressure processing (HPP) is a non-thermal food preservation technique that kills microorganisms that can cause diseases or spoil food. The state-of-the-art technology uses intense pressure for a certain time and has minimal effects on taste, texture, appearance, or nutritional values. Hence, it has emerged as an alternative to enhance food safety standards in the food system.
High-Pressure Processing: Diving Into Depth
Food Processors use HPP technology at different steps of the food processing chain, especially on pre-packed products. It helps treat raw materials such as milk, fruit juices, and smoothies and cooked products such as sliced cooked meat products and ready-to-eat meals. It eliminates the possible risk of contamination due to unfavorable microorganisms in the raw materials. Further, in the case of processed food, it reduces the contamination which originates from the manufacturing environment.
How Does HPP Work?
In High-pressure processing, the food product or raw material is packaged in a flexible container such as a pouch or plastic bottle. It is then loaded into a sample basket. This basket is then put inside a high-pressure chamber filled with a pressure-transmitting fluid such as water. A pump pressurizes the chamber with pressure-transmitting fluid and the pressure is transmitted through the package into the food. During the process of pressurization, there is a transient temperature rise in foods due to adiabatic heating. It usually stands at 3 degrees Celsius/100 MPa.
Time Limit
Under HPP, the product is pressurized, and held under pressure for a specific time, usually 2–5 minutes. It is then depressurized. After this process, the product temperature returns close to its initial value. The processed food product qualifies for storage and refrigeration.
How does HPP Inactivate Microorganisms?
The high pressure used in HPP modifies the cellular morphology of microorganisms and damages cell membranes, ribosomes, and enzymes. It also affects those microorganisms which does DNA replication and transcriptions. Hence, it checks food spoilage.
Analyzing the Applicability of HPP
Types of Products Suitable For HPP
Food Processors use high-pressure treatment for a variety of products such as value-added liquid, semi-solid, and solid foods. Some of these categories include Deli meat, guacamole, seafood, ready-to-eat meals, sauces, juices and beverages, jams, salsa, pet foods, baby foods, fruits, and vegetable products. Acidic foods (pH < 4.6) are particularly good candidates for HPP technology.
Products not Suitable for HPP Treatment
Several food products showcase limitations in terms of HPP treatment. Some of the food products with entrapped air pockets such as breads, cakes, mousse, strawberries, and marshmallows are not suitable for HPP. It is because these foods deform under pressure due to the compressibility difference between air and food. Further, foods with low moisture content such as spices, powders, and dry fruits are also not suitable for HPP. This is because the microbial lethality of pressure diminishes under low-water activity conditions.
Packaging Material for Pressure HPP Treatment
During HPP treatment, the food and packaging material may undergo a 15% volume reduction. It returns to its original volume upon depressurization. Hence, it requires that the packaging be flexible enough to withstand a transient volume reduction while under pressure. Hence, it requires vacuum packaging and flexible pouches or containers. In HPP, Polyethylene terephthalate (PET), Polyethylene (PE), Polypropylene (PP), and Ethylene vinyl alcohol copolymer (EVOH) are the commonly used packaging materials.
Significance of High-Pressure Processing
Retaining Product Quality
The use of thermal processes on food products and raw materials to kill spoilage or pathogenic bacteria often diminishes product quality. High-pressure processing (HPP) uses high pressure to kill bacteria by using pressure as the lethal agent. The process is performed in refrigerated (or ambient) temperatures. It prevents thermally induced off-flavors and retains quality attributes, especially in heat-sensitive products.
Clean Label Products
High-pressure processing can eliminate or reduce the need for synthetic additives in product formulation. It helps food processors to satisfy consumer demand for clean-label products. The treated products in this technology receive minimal or reduced thermal exposure. It helps to retain the natural characteristics of the food’s appearance, texture, and nutrition.
Shelf Life
High-pressure treatment can extend the shelf life of food products up to 120 days. The number of days depends upon the choice of process parameters and product formulation. Further, the characteristics of treatment methods such as pressure, temperature, and holding time, and product characteristics such as acidity, water activity, and composition also define shelf-life extension.
Limited Impact on Food Quality
This technology does not break the covalent bonds in foods. It has a limited effect when compared to thermal processes on low-molecular-weight compounds such as flavor compounds, vitamins, and pigments. Hence, the quality of HPP-treated food is similar to fresh food products.
New Food Textures
The HPP technology helps to create new food textures in protein- or starch-based foods. This technology helps to form protein gels and increase product viscosity by using pressure.
Conclusion
The HPP has one limitation in the form of its non-applicability on food products with entrapped air pockets. However, it enjoys various advantages over thermal treatment and other traditional methods. The loss of originality in processed food is one of the main challenges faced by the modern food processing industry and the HPP can fill this void. It can cater to a sustainable food system with originality in taste, color, and texture of food items.