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Ozone (O3) is a strong oxidant, disinfectant, refining agent, and catalyst. Since its use in drinking water sterilization in France at the beginning of this century, its sterilization applications have become increasingly widespread. In food sterilization, it was first used in 1909 in Cologne, France, for the preservation of frozen meat.
Ozone is an allotrope of oxygen. At room temperature, it is an unstable, pale purple gas with a pungent, fishy odor; in trace amounts, it has a "fresh" smell. Ozone has extremely strong oxidizing power. Its oxidation-reduction potential in water is 2.07V, second only to fluorine (2.87V), and its oxidizing power is higher than chlorine (1.36V) and chlorine dioxide (1.5V). Because of its strong oxidizing properties, ozone has a strong killing effect on bacteria, mold, and viruses; this effect is usually a combination of physical, chemical, and biological factors.
The mechanism can be summarized as follows:
Ozone readily reacts chemically with lipoproteins in bacterial cell walls or phospholipids and proteins in cell membranes, thereby damaging the bacterial cell walls and cells (i.e., the so-called bacteriolysis). This increases cell membrane permeability, causing intracellular substances to leak out and rendering the bacteria inactive.
Ozone damages or decomposes cell walls, rapidly diffuses into the cells, and oxidizes intracellular enzymes or RNA and DNA, thus killing the bacteria. Under a high-voltage, strong electric field, the gas generates pulsed corona discharge on the dielectric surface, producing high-concentration plasma. Electrons and ions are accelerated by the strong electric field and collide with gas molecules, decomposing oxygen molecules into monatomic oxygen within 10 seconds. Within several tens of seconds, atomic oxygen and molecular oxygen combine to form ozone:
O₂ + e → 2O + 2O₂ → 2O₃
Ozone is unstable in water and constantly undergoes reduction reactions, producing highly reactive, strongly oxidizing single-unit oxygen (O). In the instant of its generation, it decomposes the organic matter of bacteria and microorganisms in the water.
O3 → O2+ (O) (O)+H2O → 2HO
The half-life of ozone in water is 20 min (41 min at pH 7.6, 0.5 min at pH 10.4). Water containing ozone is called ozone water. Ozone water has a very strong sterilization effect on various pathogenic microorganisms. Ozone is unstable in water and undergoes a strong redox reaction, producing highly reactive and strongly oxidizing units of oxygen (O) and hydroxyl (OH). The redox potential of hydroxyl is 2.8V, equivalent to the oxidizing power of fluorine.
The effectiveness of ozone sterilization is mainly affected by its concentration, the type of microorganism, the contact time, temperature, pH value, the physicochemical properties of water, and impurities.
Ozone has different sterilization effects on various microorganisms. Experiments show that ozone has a strong killing effect on pathogenic bacteria and viruses in humans and animals, such as Staphylococcus aureus, Escherichia coli, hepatitis B virus, and Salmonella. It also has a strong killing effect on molds that are highly resistant to chemical disinfectants.
Temperature and humidity also affect its bactericidal and disinfectant effects. Generally, lower temperatures and higher humidity result in better bactericidal effects. Experiments have shown that when the relative humidity is less than 45%, ozone has almost no killing effect on suspended particles in the air. At the same temperature, the killing effect gradually increases when the relative humidity exceeds 60%, reaching its optimal effect at a relative humidity of 90%.
The concentration of ozone also affects its sterilization ability. At concentrations below 0.2 mg/L, it has almost no killing effect.
High Efficiency and Rapid Action
Ozone can kill 100% of bacteria, yeast, and Aspergillus niger within just 1 minute. Ozone water sterilization differs from conventional sterilization and disinfection agents, such as hypochlorous acid (HOCl₂) and chlorine dioxide (ClO₂), which are progressive and cumulative. Ozone water sterilization, however, is rapid; when the ozone concentration exceeds a threshold, disinfection and sterilization occur instantly. For example, when the ozone concentration in purified water reaches 0.4-0.5 ppm, bacteria can be killed within 0.5-5 minutes.
Safe and Reliable
The decomposition product of ozone is oxygen, leaving no residual pollution. Furthermore, as a gas, it has good diffusion and uniform concentration, making it more practical than ultraviolet lamps, especially in high-humidity environments. It is also easy to operate and safe and reliable. Ozone has no effect on the human body.
Inexpensive
Producing 1 ton of ozone water with a concentration of 0.5-1.5 ppm costs only 0.8 yuan. It is the world's cheapest disinfectant.
Since its discovery in 1785, ozone has been widely used as a gaseous disinfectant in food processing, transportation, storage, and tap water production. This is because it can disinfect and sterilize not only spaces but also surfaces and interiors of objects. Especially in recent years, with a deeper understanding of ozone utilization technology, ozone sterilization has received increasing attention in the food industry, and its application scope has expanded. Beyond sterilization, it has also shown considerable promise in deodorization and decolorization.
In countries like Japan and the United States, ozone sterilization methods are widely used in all aspects of food processing. Ozone sterilization has unique effects in many aspects of the food industry. Because ozone has a good killing effect on yeast, it is of great significance in the adoption of new food packaging. Recently, with the popularization of gas replacement packaging, vacuum packaging, packaging with oxygen absorbers, and packaging with powdered alcohol, a new spoilage phenomenon has emerged—food spoilage caused by yeast. The most representative problem is spoilage due to the production of vinyl acetate. Because ozone has a good killing effect on yeast, filling the packaging with ozone to kill yeast has become an important means of solving this problem when using the above-mentioned new packaging. Ozone also has a unique effect in solving secondary bacterial contamination during the solid food production process, which is unmatched by other sterilization methods. Therefore, in the processing of packaged foods such as raw noodles, buns, red bean paste, pickles, and tofu, workshop sterilization, ozone sterilization inside the packaging, and raw material sterilization have become very effective food hygiene methods. Satisfactory results have also been achieved in the sterilization and disinfection of containers, pipelines, equipment, and glass bottles and plastic buckets used in the production of mineral water, soft drinks, and fruit juices.
