High-Pressure Processing (HPP): Preserving Freshness, Enhancing Safety
In the realm of food processing, preserving freshness while ensuring safety is a perpetual challenge. Enter High-Pressure Processing (HPP), a cutting-edge technology that has emerged as a game-changer in the food industry. HPP employs extreme pressure to effectively extend the shelf life of food products while retaining their nutritional value, flavor, and texture, all without the need for heat or chemical additives. Let’s delve deeper into this fascinating technology and its implications for the future of food.
What is High Pressure Processing of Foods ?
HPP is the nonthermal technology of food processing i.e. It does not employed at high temperature and that is why it causes very less effects on the nutritional value of foods. The high pressure disrupts the pathogenic microbial cells, inactivate the enzymes without heat treatment and with preserving the nutritive value of foods such as flavour, aroma, texture, taste etc. It is the novel food processing technology that is applied in case of heat sensitive foods. HPP is the nonthermal food pasteurization technique that is operated at high pressure of around up to 87,000 pounds per square inch, or 6,000 atmospheres, or 600 MPa. HPP assures food safety and quality with minimal effect on the nutritional profile of food.
What is the significance of HPP in food processing ?
HPP is proved to best in case of heat sensitive foods where a huge destruction take place by thermal treatment. So, to preserve the nutritional value by killing the pathogenic microbes, HPP is the better technique than corresponding thermal techniques.
What is the working Principle of HPP ?
High-pressure processing does not operate in continuous mode but in a batch mode operation. Initially, the food is packaged in a flexible container such as in a pouch or plastic bottle and then this packaged food loaded into a sample basket. Now, this sample basket is finally loaded inside a high-pressure chamber filled with a fluid such as water that can transmit the pressure uniformly. The fluid in the chamber is pressurized with a pump, and the pressure is transmitted through the package into the food. During the process of pressurization, a small rise in temperature take place which is around 3 degrees Celsius per 100 MPa of pressure applied due to adiabatic heating. The product is pressurized usually for 2–5 minutes depending on the requirement before being depressurized. The product temperature then returns close to its initial value. The processed product is then removed and stored or distributed under refrigerated conditions.
Mechanism of HPP for microbial inactivation
The high pressure disrupts the cell wall, ribosomes, enzymes and DNA of the microbes. Due to thicker cell wall, gram positive bacteria are more resistant to the high pressure in comparison to the gram negative bacteria which have comparatively thin cell wall. Generally, gram-negative bacteria are more pathogenic and that is why HPP kills pathogenic microbes, hence it is called nonthermal pasteurization technology.
Note: If the applied pressure is inadequate, only a little injury may take place to the bacterial cell which may grow during storage period and can create food safety issues for the consumers.
Type of foods processed with HPP Technology
Generally high acidic food with pH<4.6 are most suitable for HPP technology. But liquid foods, semisolid foods and solid foods can be pasteurized with HPP such as fruits and vegetable juices, sauces, ready to eat food products, jams, jellies, baby foods, meat products, sea foods etc.
Foods not suitable for HPP technology
Two types of foods are not suitable for high pressure processing
- Foods with low moisture content or water activity: For effective application of high pressure technology, foods must contain considerable amount of moisture or water activity. So, the foods with low moisture or water activity are not suitable for high pressure processing such as dry foods, spice powders etc.
- Foods with entrapped air inside food matrix: The food products which have air pockets entrapped inside their matrix are not the suitable foods because when a high pressure is applied during pressurization process, the foods can be deformed or shape change drastically which is not desirable by the consumer such as bread, cakes, other bakery products, strawberries etc.
Suitable packaging material for HPP
The suitable packaging material for high pressure processing must have two properties:
- Packaging material with high flexibility: As during high pressure processing, we kill the microbes through pressurization techniques which is passed to food through pressure transmitting fluid. So, the packaging material must be flexible enough to withstand the applied pressure and can easily regain its original shape after depressurization. The most common packaging materials used are Polyethylene terephthalate (PET), Polyethylene (PE), Polypropylene (PP), and Ethylene vinyl alcohol copolymer (EVOH). Eco-friendly options such as rPET and PLA are also suitable.
- Packaging material with high barrier properties: As during high pressure processing, the pressure is transmitted through a liquid. So, the packaging material must have good barrier properties for water and oxygen for assuring the food safety and quality aspects.
Expected shelf life of HPP Food Products
The shelf life of HPP food products depends upon following factors:
- Operating conditions: shelf life of the HPP food products depends upon applied pressure, temperature and holding time of food inside pressure chamber.
- Food Formulation: The food formulation such as water activity, composition and acidity affect the shelf life of the product.
- Type of packaging material: Type of packaging material also affect the shelf life of HPP product.
- Storage condition: After high pressure processing, the storage condition also play important role in shelf life the product i.e. optimum condition extend the shelf life of the product. Generally, high pressure processed food products may have maximum of 120 days of shelf life.
HPP as commercial sterilization of low acid foods
Bacterial spores may survive inside low acid food environment (pH<4.6). So, to kill bacterial spores only application of high pressure is not sufficient. For effective spore killing high pressure application combined with high temperature treatment. For spore inactivation, a 400-600Mpa pressure, 90-120 C temperature are used for 3-15 minutes. This is called pressure-assisted thermal process (PATP).