Pascalization, bridgmanization, high pressure processing (HPP) or high hydrostatic pressure (HHP) processing 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. HPP has a limited effect on covalent bonds within the food product, thus maintaining both the sensory and nutritional aspects of the product. The technique was named after Blaise Pascal, a 17th century French scientist whose work included detailing the effects of pressure on fluids. During pascalization, more than 50,000 pounds per square inch (340 MPa, 3.4 kbar) may be applied for approximately fifteen minutes, leading to the inactivation of yeast, mold, vegetative bacteria, and some viruses and parasites. Pascalization is also known as bridgmanization, named for physicist Percy Williams Bridgman. Depending on temperature and pressure settings, HPP can achieve either pasteurization-equivalent log reduction or go further to achieve sterilization, which includes killing of endospores. Pasteurization-equivalent HPP can be done in chilled temperatures, while sterilization requires at least 90 °C (194 °F) under pressure. The pasteurization-equivalent is generally referred to as simply HHP (along other synonyms listed above), while the heated sterilization method is called HPT, for high pressure temperature. Synonyms for HPT include pressure-assisted thermal sterilization (PATS), pressure-enhanced sterilization (PES), high pressure thermal sterilization (HPTS), and high pressure high temperature (HPHT).
Uses
HHP (pasteurization-equivalent) Spoilage microorganisms and some enzymes can be deactivated by HPP, which can extend the shelf life while preserving the sensory and nutritional characteristics of the product. Pathogenic microorganisms such as Listeria, E. coli, Salmonella, and Vibrio are also sensitive to pressures of 400–1000 MPa used during HPP. Thus, HPP can pasteurize food products with decreased processing time, reduced energy usage, and less waste. The treatment occurs at low temperatures and does not include the use of food additives. From 1990, some juices, jellies, and jams have been preserved using pascalization in Japan. The technique is now used there to preserve fish and meats, salad dressing, rice cakes, and yogurts. It preserves fruits, vegetable smoothies and other products such as meat for sale in the UK. An early use of pascalization in the United States was to treat guacamole. It did not change the sauce's taste, texture, or color, but the shelf life of the product increased from three days to 30 days. Some treated foods require cold storage because pascalization cannot destroy all proteins, some of them exhibiting enzymatic activity which affects shelf life. In recent years, HPP has also been used in the processing of raw pet food. Most commercial frozen and freeze-dried raw diets now go through post-packaging HPP treatment to destroy potential bacterial and viral contaminants, with salmonella being one of the major concerns.
HPT (commercial sterility) Low-acid food require the killing of endospores to become shelf-stable. Addition of heat on top of pressure, as in HPT, achieves this goal. In 2009, FDA issued no objections to a petition for using HPT, specifically the type known as PATS, on mashed potato. In 2015, the FDA issued another no-objection for PES, another type of HPT, on seafood. Application of HPT to other types of fruit is still being explored.
Other uses A short-duration application of HHP is able to separate the meat of shellfish from their shells, making hand-peeling much easier. HHP also inactivates Vibrio bacteria. HHP is used in 7% of seafood and shellfish.
History
Late 19th century Experiments into the effects of pressure on microorganisms have been recorded as early as 1884, and successful experiments since 1897. In 1899, B. H. Hite was the first to conclusively demonstrate the inactivation of microorganisms by pressure. After he reported the effects of high pressure on microorganisms, reports on the effects of pressure on foods quickly followed. Hite tried to prevent milk from spoiling, and his work showed that microorganisms can be deactivated by subjecting it to high pressure. He also mentioned some advantages of pressure-treating foods, such as the lack of antiseptics and no change in taste. Hite said that, since 1897, a chemist at the West Virginia Agricultural Experimental Station had been studying the relationship between pressure and the preservation of meats, juices, and milk. Early experiments involved inserting a large screw into a cylinder and keeping it there for several days, but this did not have any effect in stopping the milk from spoiling. Later, a more powerful apparatus was able to subject the milk to higher pressures, and the treated milk was reported to stay sweeter for 24–60 hours longer than untreated milk. When 90 short tons (82 t) of pressure was applied to samples of milk for one hour, they stayed sweet for one week. The device used to induce pressure was later damaged when researchers tried to test its effects on other products. Experiments were also performed with anthrax, typhoid, and tuberculosis, which was a potential health risk for the researchers. Before the process was improved, one employee of the Experimental Station became ill with typhoid fever. The process that Hite reported on was not feasible for widespread use and did not always completely sterilize the milk. While more extensive investigations followed, the original study into milk was largely discontinued due to concerns over its effectiveness. Hite mentioned "certain slow changes in the milk" related to "enzymes that the pressure could not destroy".
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