Ozone (O3) is a potent oxidant allotropical form that produces oxygen through lightning reactions or ultraviolet irradiation. O2 divides in extremely reactive single oxygen during ozone generation, which then reacts to the formation of ozone with additional oxygen molecules. Ozone offers a very quick response and a very powerful oxidative quality to the processing and preservation industries, ensuring microbiological food safety. In addition, molecular oxygen swiftly auto-decomposes, leaving no dangerous halogenated chemicals in the food products. It eliminates several kinds of microorganisms at relatively low levels and meets worldwide sustainability demand. Organic compounds are oxidized into safer elements by ozone. Conventional methods, including the use of moderate thermal treatments, are routinely employed to increase the shelf life of these products. Heat processing can however produce a number of biological, physical, chemical, and microbiological changes that may have a negative impact on the quality of the product.
Ozone may be produced in numerous ways. Experiments in the air or other gas mixtures that contain oxygen can provide an energy source such as a high-energy electric field (corona release process), UV light (phytochemical methods), or oxygen molecules (O2) to ozone (O3) (chemical method). However, due to its quick deterioration to oxygen, it should be created soon before usage. Ozone must be created continuously if needed as it cannot be stockpiled. Other ways of ozone creation include electrolysis, water reaction, and radiochemical production of the elemental phosphorus.
An oxygen-based gas mixture or O2 itself travels between two electrodes that are typically glass, separated by a dielectric material, via the high-energy electrical field. This is the main idea of corona discharge. One electrode is a sub-structured media, and a dielectric medium is the other. The key is to manage the temperature of the treated gas as ozone can be degraded by heating, i.e., endothermically. If around 80% of the energy is exceeded, then heat is transferred and a spontaneous decomposition of ozone into oxygen ions and molecules, especially above 35°C, is then produced, if not removed.
- Ultraviolet technology-
UV light is used to make ozone by ultraviolet technology at wavelengths between 140 and 190 nm. During the process of separating oxygen molecules into their constituent atoms, some of them (O2) become unstable radical oxygen atoms (O1). This reaction produces free radical oxygen atoms, which bind to O2 molecules and respond to other diatomic oxygen molecules, resulting in O3 or ozone molecules being formed. Both ozone synthesis and air purification use mercury lamps of low pressure. High-transmission UV lamps have the benefit of emitting two high-efficiency resonance lines at wavelengths of 185 and 254 nm from their mercury release emissions spectra.
Oxygen is drawn from the atmosphere and concentrated for ozone production via an ozonation device. The treatment chamber (collector) receives the ozone, which is generated, measured, and used to inactivate microorganisms. Excess ozone from the treatment chamber is converted to oxygen before being released into the atmosphere to prevent health risks. The components of a gaseous ozone ozonation system for use in food processing industries include the following:
- Oxygen concentrator- These devices take in ambient air, automatically filter (remove dust particles), then separate and remove nitrogen (thereby leaving air considerably enriched with oxygen), which is also dried to below the desired maximum dew point (4°C), all at the same time in one small device. These oxygen concentrators operate on the principle of pressure swing adsorption (PSA) drying.
- Ozone generator- Ozone generators may be UV generators or Corona discharge generators. The two common types of gas preparation to feed CD ozone generators are oxygen and dry air. UV generators of ozone do not require any special air preparation.
- Flow meters– Mass flow meter provides accurate measurement of total oxygen gas flow from the oxygen concentrator to the ozone generator. The ozone flow meter uses a small gas stream (less than 2 LPM) to measure ozone concentration and for the regulation of gas flow through an ozone analyzer.
- Treatment chamber- It is the collector where ozone enters from the top and returns through the bottom outlet after completing the exposure time. The chamber is air-tight and avoids leakages. The dimension and type will be based on the mode of application of ozone and the type of product being processed.
- Ozone analyzer- The ozone concentration in percent weight, or g/m3, that enters and leaves the treatment chamber will be measured using this instrument.
- Ozone destructor- At the outlet of the destructor, excess ozone is destroyed, and the cleaned and decontaminated air is re-circulated to its intended enclosure or discharged to the ambient atmosphere. Destructor is an important part that assures non-hazardous by-products or waste in ozone treatment.
SAFETY AND LEGAL ASPECTS
Ozone treatment has been outspread in recent years for seeking ‘greener’ food additives. Due to that fact, many consumers express their concerns about the ingredients of the consumed food, as well as each operation which is responsible for bringing food ‘from farm to fork’.On 26 June 2001, the USFDA has accorded Generally Recognized As Safe (GRAS) status for ozone and approved its use as an antimicrobial agent during the processing and storage of food products.Whatever form of ozone is applied in food, its health and safety aspects also apply to the workers. Among all disinfectants, ozone is unhealthy for humans who are expected to experience exposure to it in sufficient concentrations for sufficient periods of exposure.
APPLICATION OF OZONE TECHNOLOGY
Ozone is a potential fumigant for managing the stored product insect pests and a powerful antimicrobial agent which has a minimal or no effect on grain quality. Ozone treatment of grain is generally applied in the hermetic storage bin at a stipulated grain moisture content and minimum bed thickness. Another area of the potential use of ozone treatment is its anti-fungal activity in stored grains. As fungal infection of grains depends on many factors such as cultural practices, weather parameters, storage conditions, and innate resistance of the plants, ozone could be potentially used in treating fungi of stored grains.
- Fruits and Vegetables
Fruits and vegetables are highly susceptible to spoilage causing micro-organisms. Ozone exposure is a viable alternative in preserving various food products such as juice, ice cream, jam, jellies, sorbet, pickles, and nutraceutical applications. Ozone treatment is used in fruit and vegetable processing in order to inactivate the pathogenic and spoilage-causing microorganisms, mycotoxins and to destroy pesticide and chemical residues. It is preferred because of the absence of residual effect of chlorine, even at low concentrations, associated with the most popular disinfectants.
- Dairy Products
Ozone is used in the dairy industry for a variety of purposes such as surface decontamination, removing soil from processing surfaces, ensuring microbial safety, etc.As the dairy industry usually employs hot water and chemical wash for this purpose, the above method decreased the chemical usage and almost eliminated the hot water cost on cleaning in the dairy industry.Ozone can also be used as a pre-treatment of fluid milk before pasteurization to maintain its shelf life. Being a powerful oxidizing agent, when comes in contact with protein, it can affect the peptide backbone, cause bond cleavage, and modification of amino acid side chain. This reaction can later alter the functional properties of proteins such as foaming and emulsifying ability.
- Meat, Poultry, and Seafood
The spoilage of meat and meat products is associated majorly with the activity of microorganisms and their enzymes to a certain extent. Ozone is found to have a positive hand in controlling the microbial populations that were present internally or added to the system viva poor handling and processing steps. The effect of ozone is not only limited to fresh carcasses but also the processed set of meat and meat products. A major issue associated with the consumption of meat is an illness that ensues due to contamination of meat with Campylobacter, E.coli, Listeria, and Salmonella. Ozone has been tested for disinfecting hatching eggs, poultry carcass, poultry chiller water, and contaminated eggs. Seafood products are one of the principal sources of protein content and hence preservation of seafood is a research priority in the food industry. Ozone treatment also contributes to the maintenance of the quality of seafood products.
Department of Dairy Science and Food Technology