Pascalization

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 French scientist of the 17th century 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 around fifteen minutes, leading to the inactivation of yeast, mold, and bacteria. Pascalization is also known as bridgmanization, named for physicist Percy Williams Bridgman. 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 French scientist of the 17th century 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 around fifteen minutes, leading to the inactivation of yeast, mold, and bacteria. Pascalization is also known as bridgmanization, named for physicist Percy Williams Bridgman. 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. HPP is now being used to preserve fruit and 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 guacamole's taste, texture, or color, but the shelf life of the product increased to thirty days, from three days without the treatment. However, some treated foods still require cold storage because pascalization does not stop all enzyme activity caused by proteins, some of 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 bacteria and viruses contaminants, with salmonella being one of the biggest concerns. 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. Unfortunately, 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. Indeed, 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'. Hite et al. released a more detailed report on pressure sterilization in 1914, which included the number of microorganisms that remained in a product after treatment. Experiments were conducted on various other foods, including fruits, fruit juices, and some vegetables. They were met with mixed success, similar to the results obtained from the earlier tests on milk. While some foods were preserved, others were not, possibly due to bacterial spores that had not been killed. Hite's 1914 investigation led to other studies into the effect of pressure on microorganisms. In 1918, a study published by W. P. Larson et al. was intended to help advance vaccines. This report showed that bacterial spores were not always inactivated by pressure, while vegetative bacteria were usually killed. Larson et al.'s investigation also focused on the use of carbon dioxide, hydrogen, and nitrogen gas pressures. Carbon dioxide was found to be the most effective of the three at inactivating microorganisms. Around 1970, researchers renewed their efforts in studying bacterial spores after it was discovered that using moderate pressures was more effective than using higher pressures. These spores, which caused a lack of preservation in the earlier experiments, were inactivated faster by moderate pressure, but in a manner different from what occurred with vegetative microbes. When subjected to moderate pressures, bacterial spores germinate, and the resulting spores are easily killed using pressure, heat, or ionizing radiation. If the amount of initial pressure is increased, conditions are not ideal for germination, so the original spores must be killed instead. However, using moderate pressure does not always work, as some bacterial spores are more resistant to germination under pressure and a small portion of them will survive. A preservation method using both pressure and another treatment (such as heat) to kill spores has not yet been reliably achieved. Such a technique would allow for wider use of pressure on food and other potential advancements in food preservation.