Mitsubishi Electric Develops a Safe and Effective Sterilization Technology Using a Combination of Negative Ions and Ozone

Tokyo, October 23, 1997 -- Mitsubishi Electric Corporation has discovered that, when using a combination of negative ions*¹ (10⁶ parts/cm³) and a low concentration of ozone*² (0.03 ppm, less than the working environment standard*³), sterilization ten times more effective was achieved than when compared with the use of either one or the other on its own, and has thus developed a new sterilization technology that sterilizes foodstuffs both safely and effectively through the simultaneous generation of a fixed quantity of negative ions and ozone.

Up until now, the sterilization effects have been proven against various microbes and fungi including the E. coli O-157 pathogen, and experiments have confirmed that the technology is also effective in the preservation of meat, fish, and fruit. The technology that has been developed, sterilizes the surface of the object both safely and effectively, without altering either its quality or its color, for which reason, it can preserve foodstuffs in their ideal state. Mitsubishi Electric will begin its presentations for clients in November 1997, when the company is scheduled to conduct experiments that offer conclusive proof at the locations of clients from various fields such as meat packing plants, and the preservation and storage of fruit and vegetables.

Background

Outbreaks of microbial contamination and infection, as well as contamination of foodstuffs due to the E. coli O-157 pathogen and contamination within hospitals due to MRSA*⁴ has become a major social problem. Normally, disinfectant and ozone are used to sterilize microbes, but disinfectant has the problem of residual contamination itself. Alternatively, ozone is a powerful disinfectant because of its oxidation, but the advisable working environment standard is set at 0.1 ppm, and also, at quantities of 0.2 ppm or more foodstuffs are discolored and processing vessels suffer from both oxidization and corrosion. Therefore, only a low concentration can be used, such that adequate sterilization cannot be achieved.

Mitsubishi Electric has been promoting research into foodstuff preservation technology using negative ions. Negative ions are used in air purifiers and other similar equipment, and are safe compared to ozone, but it is understood that they can only suppress the breeding of bacteria, that is, only maintain bacteriostasis and in addition, cannot even achieve any bacteriostatic effect on powerful microbes such as O-157 or Staphylococcus aureus. For that reason, a safe and effective sterilization technology was required that would have no effect on foodstuffs, while achieving the same quality of sterilization as ozone.

Main features and results

In this experiment, when 0.03 ppm of ozone was added to 10 thousand times the concentration of negative ions (10⁶ parts/cm³) naturally occurring in the world, it was found that a clearly far greater sterilization capability could be achieved as oposed to using either of these elements as disinfectants on their own. The mechanism for simultaneously generating a fixed quantity of negative ions and ozone in a single generator was developed by analyzing the generative characteristics of both the negative ions and ozone. The sterilization technology developed in this experiment has the heretofore unseen ability to sterilize bacteria on the surface of any given foodstuff, while having no effect on the foodstuff itself.

1. Discovery of an exponential increase in sterilizing power through the combined use of negative ions and ozone

When negative ions (10⁶ parts/cm³) and a low quantity of ozone (0.03 ppm) were combined, it was discovered that a tenfold increase in sterilization effectiveness could be obtained rather than when compared with using either negative ions or a low concentration of ozone on its own. It is safe to say that generally, a sterilization rate of 90% or more was achieved, but the result of processing Staphylococcus aureus, (which causes severe food poisoning, for three days at 20°C and 90% humidity, a sterilization rate of less than 10% was achieved when using either negative ions or a low concentration of ozone on their own, however, an almost perfect sterilization rate of 94% was achieved using a gas that was a combination of the two.

Basic experiments that used not only Staphylococcus aureus, but also E.coli, (which is an index bacteria in food contamination), bacillus subtilis spores, (which are the most difficult to sterilize), and pseudmonas*⁵, (which thrives at low temperatures), confirmed the sterilizing effect when both negative ions and a low concentration of ozone are used in combination.

2. Development of technology that simulataneously generates both high concentrations of negative ions and extremely low concentrations of ozone

The generative characteristics of negative ions and ozone during a corona discharge*⁶of electricity in the atmosphere were analyzed, and the makeup of the polarities, materials, and power specifications were optimized; these proved to be a high concentration of negative ions at 10⁶ parts/cm³, which is close to its limit, and a low concentration of ozone which, at 0.03 ppm, is below the working environment standard (0.1 ppm). Equipment that could simultaneously generate these quantities was then developed. The frequency of the direct current power pulse and the applied voltage were then optimized, and while generating high concentrations of negative ions, a low concentration of ozone was constantly maintained at below the working environment standard. The equipment was kept running continuously for a period of one year, thereby confirming stable operation for long periods.

3. Safe and effective sterilization without discoloring the foodstuffs

Experiments were conducted on real foodstuffs into the effects of combined processing using both negative ions and ozone. In the case of pork and tuna fish, not only was there a reduction in the amount of bacteria, but no discoloration or abnormal smell could be detected when processing with ozone at 0.2 ppm. An outbreak of fungi was also prevented on strawberries, and it was determine that the effect on the foodstuff itself was to the same level as when using negative ions alone, and that there was almost no reduction in vitamins. Further, with the objective of the preservation of fruit over a long period of time, experiments were conducted on stored fruit such as grapes, cherries, and plums in cooperation with the Ministry of Agriculture, Forestry and Fisheries' fruit testing site. To date, the outbreak of fungi has been prevented on the surface of grapes for a period of eight months. In this way, the preservation of foodstuffs is effective because it is possible to sterilize the surface of the foodstuff alone without affecting the foodstuff itself.

4. Sterilization of the pathogen E.coli O-157 also proven

As a result of experiments using the pathogen E-coli O- 157, which has become a major social problem in recent years, and acting under guidance from the Osaka Prefectural Institute of Public Health, it was proven that sterilization of this bacteria was also possible. Because it is possible to sterilize O-157, this process is also effective in the hygiene management of foodstuffs.

Further developments

1. Elucidation of the sterilization mechanism using a combination of both negative ions and ozone

The sterilization mechanism generates hydroxyl radicals (OH radicals)*⁷ with greater oxidization and sterilization power than mere ozone alone through a reaction between negative ions and ozone, and it is believed that this attacks the bacteria on the surface of the foodstuffs. Based on this hypothesis, further research to elucidate the sterilization mechanism is planned for the future.

2. Verification experiments will begin at our clients' locations from November 1997

Mitsubishi Electric is scheduled to conduct experiments that offer conclusive proof at the locations of clients from various fields such as meat packing plants, and the preservation and storage of fruit and vegetables.

Glossary

1. Negative ion:

When an electron collides with either a neutron or an atom, the particle that bonds to the electron becomes a negative ion. This is limited only to atoms and molecules to which electrons can bond, and matter which is ionized especially easily including oxygen, water vapor, halogen gas, and sulfur hexafluoride. In the atmosphere, there are many instances of oxygen being negatively ionized helping to form the ozone layer. Also, the concentration of negative ions in the natural world is normally to the order of 100 parts/cm3.

2. Ozone (O3):

Ozone is an allotrope of oxygen, and is a gas with a powerful oxidization decomposition second only to fluorine. Industrially, it is generated using "voiceless electrical discharge" (explanation necessary) as a source gas for either dry air or oxygen. Because ozone breaks down and returns to oxygen, there is no residue, and it is currently used to purify water in swimming pools and aquariums, and to remove fungus smells from water pipes and aqueducts.

3. Working environment standard:

The Japan Society for Occupational Health set the recommended tolerable concentration of ozone at 0.1 ppm in 1985. This value of 0.1 ppm is the environmental standard when working in a non physically demanding job for a working week of up to 40 hours at a period of eight hours per day. If the arithmetical mean of the exposure concentration is at this value or less, it has been determined that there is no effect upon the health of almost all workers.

4. MRSA (Methicillin-Resistant Staphylococcus Aureus):

The Methicillin-Resistant Staphylococcus Aureus, which is immune to antibiotics, can have major harmful effects on patients with a weak disposition.

5. Pseudmonas genus of bacteria:

The pseudmonas is one genus of bacteria that is widespread in both the earth and in water. There are many recorded instances of it flourishing under conditions of low concentrations of nutrition where other microorganisms have difficulty in breeding, and there are also times when it acts as a parasite on both plants and animals, so that it is claimed to be comparatively difficult to sterilize.

6. Corona electrical discharge:

The electrical field between two flat poles is equal, excluding the area around the contacts of the poles themselves, but when voltage is applied between a flat pole and a needle (or a wire), a remarkably uneven electrical field is generated. When the electrical field is remarkably uneven, ionization only occurs in the strong part of the field, and partial electrical discharge, namely, local electrical discharge, is the result. This type of electrical discharge is called corona electrical discharge.

7. Hydroxyl radicals (OH radicals):

When over-oxidized hydrogen is added to ozone, the ozone is broken down by ultra-violet rays and reacts with water, generating hydroxyl radicals (OH radicals). OH radicals are more powerful oxidizers than ozone, and react rapidly with organic materials.