[4] 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,[5][6] and some viruses and parasites.
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.
[7] 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.
[5] Some treated foods require cold storage because pascalization cannot destroy all proteins, some of them exhibiting enzymatic activity[14] which affects shelf life.
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.
[20] 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.
[22] 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.
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.
[28][dubious – discuss] Research into the effects of high pressures on microorganisms was largely focused on deep-sea organisms until the 1980s, when advancements in ceramic processing were made.
This resulted in the production of machinery that allowed for processing foods at high pressures at a large scale, and generated some interest in the technique, especially in Japan.
In pascalization, food products are sealed and placed into a steel compartment containing a liquid, often water, and pumps are used to create pressure.
[10] Pascalization works especially well on acidic foods, such as yogurts and fruits,[3] because pressure-tolerant spores are not able to live in environments with low pH levels.
[30] This involves pressurization of liquid foods up to 400 MPa and subsequent depressurization by passage through tiny clearance in a shear valve.
Remaining kinetic energy is spent on sample physical and structural modifications (mixing, emulsification, dispersion, particle size, enzyme, and microbial reduction) via intense mechanical forces, such as shear, turbulence, or cavitation.
Thus, depending upon the product's initial temperature and process pressure, UST treatment can result in pasteurization or commercial sterilization effects along with structural modification in the treated liquid.
[10] High hydrostatic pressure can affect muscle tissues by increasing the rate of lipid oxidation,[33] which in turn leads to poor flavor and decreased health benefits.
[35] Because hydrostatic pressure is able to act quickly and evenly on food, neither the size of a product's container nor its thickness play a role in the effectiveness of pascalization.
There are several side effects of the process, including a slight increase in a product's sweetness, but pascalization does not greatly affect the nutritional value, taste, texture, and appearance.
[25] Anurag Sharma, a geochemist; James Scott, a microbiologist; and others at the Carnegie Institution of Washington directly observed microbial activity at pressures in excess of 1 gigapascal.
There is practically no debate on whether microbial life can survive pressures up to 600 MPa, which has been shown over the last decade or so to be valid through a number of scattered publications.