New method of sterilisation by shockwave will eventually replace pasteurisation
Shockwave technology is already being used to destroy many common food bacteria. If the technology is further improved, it will replace pasteurisation for baby food, dairy products and fruit juices, while still retaining the original flavour.
Yazimu Roscoe of the Mexican Centre of the Department of Applied Physics and High Technology at the Autonomous University of Querétaro and his colleagues have studied this technology. Roscoe placed a bottle of bacteria in an electro-hydraulic generator device, which generates shock waves as high as 1,000 atmospheres, accompanied by violent sparks of visible and invisible light.
Roscoe says this combination kills the bacteria in the bottle. The potential advantage of this treatment is that, as we know, the shock waves do not alter the taste of the food.
The shock wave causes tiny bubbles in the liquid around the bacteria to instantly expand and burst, a process also known as cavitation, resulting in high heat in a small area.
It combines with the pressure of the shock wave and the violent impact of visible and invisible light to kill the bacteria. Roscoe says this is the result of a combination of compression, cavitation and electromagnetic radiation.
The system needs further refinement because it does not yet kill the bacteria completely. At the moment it is very effective against Listeria monocytogenes, a food-borne bacterium that can cause miscarriages. It is not effective against E. coli O157:H7, which causes lethal food poisoning.
After 350 blasts for 15 minutes, the number of bacteria is reduced to one thousandth of its original size. Roscoe is confident that with improved technology it could be reduced to one in a million, which would be sufficient for food sterilisation. The problem now, he says, is to increase the energy and number of blasts. The ability to kill Listeria monocytogenes is already sufficient.
His team is also looking at how the shockwave sterilises. He says we don't yet know if it is cheaper than the traditional process. Morse Solomon, of the US Agricultural Research Service Laboratory's Food Safety**, says it is important to understand how the technology works if it is to be marketed.
Solomon's research team has experimented with cooking meat with tiny explosions that also killed some bacteria, but not enough to be worthy of practical application.
Mexican scientists recently made an interesting attempt to use shock waves to sterilise food for the first time. If this technique is further refined, it may one day be possible to replace pasteurisation to sterilise baby food, dairy products and fruit juices without destroying their original taste.
The technique was developed by Achim Loske and his colleagues at the Universidad Autónoma de México, who placed vials of bacterial samples into a device called an electro-hydraulic generator, which produces a shock wave of up to 1,000 atmospheres of pressure, accompanied by intense visible light and ultraviolet lightning. The pressure wave causes tiny bubbles in the liquid surrounding the bacteria to expand rapidly and then explode violently, a process known as the "cavitation" phenomenon, which creates high heat over a small area.
Loske says that it is the combination of intense pressure, the "cavitation" phenomenon and electromagnetic radiation that succeeds in killing the bacteria in the bottle. And the great thing about this technique** is that the shock wave sterilisation method does not change the taste of the food. Their findings will be published in an upcoming issue of the journal Innovative Food Science and Technology.
However, the system needs to be further refined, as it currently does not kill enough bacteria to provide people with completely safe food. Studies have shown that it is very effective against some types of bacteria, but does not work satisfactorily against others. **In the best case scenario, the shockwave can reduce the number of bacteria by **one thousandth in a 15-minute period. But Loske says that with device improvements he is very confident of increasing the germicidal rate by a factor of several million. "It's a question of increasing the energy level and dose of the shock wave, which we have initially verified in the laboratory."
Loske and others are currently working on the exact mechanism of shockwave sterilisation.
