Department of Postharvest Technology, College of Horticulture, UHS campus, GKVK post, Bengaluru-65
High Pressure Processing (HPP) is a promising “non-thermal” technology that has been developed with the aim of obtaining microbiologically safe food products while avoiding undesirable changes in the sensory, physicochemical, and nutritional properties of foods. Thus HPP has become one of the innovative food processing technologies most accepted by consumers.
- First research on HPP was conducted in 1890s against Milk Pathogens.
- First commercialized in Japan in the early 1990s for pasteurization of acid foods for chilled storage.
- High pressure treated foodstuffs have been marketed in Japan since 1990, in Europe and the United States since 1996 & Australia since 2001.
High pressure processing of food
High pressure processing (HPP), is a method of preserving and sterilizing food, in which a product is processed under very high pressure, leading to the inactivation of certain microorganisms and enzymes in the food. It is also known as Pascalization. In this process, high Pressures are applied at short periods of time (20minutes).High pressure can kill microorganisms by interrupting their cellular function without the use of heat that can damage the taste, texture, and nutrition of the food.USDA has approved HPP as an intervention method for listeria contaminated pre-packed ready-to-eat (RTE) meat products and also recommended for commercial use in low acid foods.
Main features of HPP
Application of high pressures can cause:
- Inactivation of parasites, vegetative micro-organisms, fungal spores and food borne viruses;
- Enzymes are selectively inactivated
- Small molecules (Eg. flavors) are generally unaffected
- High pressure is instantaneously and uniformly applied to the sample.
- Compression is fully reversible.
How much pressure?
Pressures exerted at highest altitudes (0.01 to 0.1 MPa) and deepest part of the oceans (10-100 MPa) are usually considered as High pressures.For food processing, 200-800MPa pressure is required.For inactivating milk enzymes; alkaline phosphatase and protease about 1000 MPa is needed (as per research articles).Usually, 600MPa is the optimum pressure for processing commercial food products.
Principle behind HPP
- Le Chatelier’s principle: Any phenomenon (phase transition, change in molecular Configuration, chemical reaction) accompanied by a decrease in volume is enhanced by pressure. Accordingly, pressure shifts the system to that of lowest volume.
- Isostatic principle:Food products are compressed by uniform pressure from every direction and then returned to their original shape when the pressure is released. The products are compressed independently of the product size and geometry because transmission of pressure to the core is not mass/time dependent thus the process is minimized. If a food product contains sufficient moisture, pressure will not damage the product at the macroscopic levels as long as the pressure is applied uniformly in all directions.
Working and Equipment
A typical HPP batch system consists of four key components:Pressure vessel, Pressurization fluid, Intensifier, Pump.
- A typical HPP process uses food products packaged in a high-barrier, flexible pouch or a plastic container. The packages are loaded into the high-pressure chamber.
- The vessel is sealed and the vessel is filled with a pressure transmitting fluid (normally water).
- Pressurized by the use of a high-pressure pump, which injects additional quantities of fluid. The packages of food, surrounded by the pressure-transmitting fluid,are subjected to the same pressure as exists in the vessel itself.
- After holding the product for the desired time at the target pressure, the vessel is decompressed by releasing the pressure-transmitting fluid.
- Approximately 5–6 cycles/hrare possible, allowing time for compression, holding, decompression, loading, and unloading.
- After pressure treatment, the processed product is removed from the vessel and stored/distributed in a conventional manner.
Fig. 1: Parts and model of High Pressure Processing (HPP) Equipment
Fig. 2: Schematic flow of food in High Pressure Processing (HPP) process
Foods suitable for HPP
HPP finds application in food preservation in many ways. Some example of areas where HPP has more potential are fruits and vegetables industry, meat and fish, dairy Industry
- Low-medium moisture, semi-solid/solid foods, vacuum packaged viz., Dry-cured or cooked meat products, cheese, seafood, marinated products, ready to eat meals, sauces etc.
- High moisture, solid foods, vacuum packagedviz.,Fruits, marmalades/jams and
- High moisture, liquid foods in plastic bottle/flexible packaging,Dairy products, fruit juices and bioactive beverages.
- Solid foods with air included in them like bread and cakes, mousse.
- Packaged foods in completely rigid packagingviz., glass packaging and canned foods
- Foods with a very low water contentviz., spices, dry fruits and powders.
Applications of HPP
Fruits and Vegetables:
- For extension of shelf life
- Inactivate microorganisms and quality-deteriorating enzymes
- Higher sensorial, functional and nutritional values while improving food safety.
- Puree, sauces, juices, smoothies, chunks, slices, ready-to-eat products, these are only some examples of a wide range of fruit and vegetable products that can be processed by HPP.
- One of the most successful commercial application of HPP nowadays is definitely preservative-free guacamole (avocado puree with spices) because the process maintains avocado flavor, texture, green color without sacrificing food safety or shelf life (upto 6 weeks under chilled conditions).
- Increased shelf-life (3 to 10 times) and product freshness.
- No impact on sensory, nutritional, or functional properties.
- Effective elimination of spoilage and pathogenic microorganisms.
- High Pressure Process Technology works especially well on acidic dairy products such as yogurt because most pressure-tolerant spores are unable to survive in environments with low pH levels.
- HPP is the best option to preserve and respect the functionality of thermosensitive bioactive components present in colostrum such as immunoglobulins, lactoferrin and growth factors.
Packaging requirements for HPP:
- Flexible packaging (>15% volume contraction) with extra tight seals.
- Rounded & reinforced edges.
- Minimal head space with creation of modified atmosphere
- Tear strength, puncture resistance and surface smoothness generally not affected by HPP.
- Often flexible pouches or bottles are inserted in secondary cardboard containers after processing.
- Plastic-Laminated Materials: Nylon/Coextruded Ethyl Vinyl Alcohol (EVOH), Nylon/PP, Nylon/ Aluminum Oxide (ALOx) /CPP, PET/PE, Aluminum foil-Laminated Pouches, PET/AI/PP, Nylon/AI/PP are commonly used for packaging
Consumers: HPP is a consumer acceptable, environmental friendly,scientifically recognized method to achieve higher quality in certain foods. Processing: Pressure transmission is instantaneous, uniform, short processing times, assured safety in whole pack, suitable for solids andliquids. Quality: Retains flavor and nutrition. Environmentally: Safe and no process by‐products, no emissions.