Concerns about extending shelf life and controlling the decay and ripening of produce without depending on harmful chemicals have driven increased demand for safe, proven food storage alternatives. Service providers offer on-site ozone generating systems to deliver low-dose concentrations of gaseous ozone into storage rooms as a method of safe disinfectant. Ozone kills airborne and surface microorganisms, shuts down the sporulation process, and consumes ethylene produced by ripening. After oxidizing microorganisms, ozone immediately reverts to pure oxygen, leaving no residue and maintaining taste, texture and smell characteristics in the product’s natural state. Growers, packers, and processors are able to extend product life and marketability, as well as decrease decay losses of fresh produce naturally.
Fixed ozone monitors which control ozone generators are mission critical in cool storage rooms. Too little O3 and the benefits are lost, too much and the produce can be damaged. Portable ozone monitors can be useful for spot checks, verifying the fixed monitors, checking zones of the room not covered by fixed monitors and general health & safety. An ozone monitor located close to the generator is recommended as a safety measure to shut the generator down in case of a leak. These types of applications often require dust and water protection to reduce sensor contamination and extend the life of the sensor.
Why Ozone Processing of foods?
On June 26, 2001, the U.S. FDA approved ozone, a gas that is a strong oxidizing agent capable of acting as a disinfectant and antimicrobial agent for direct contact with food. Ozone can control microorganisms of all types without producing halogenated byproducts. Ozone uses include the treatment of bottled water, soft drinks, process water for reuse, cooling tower water, water for washing of food processing and handling equipment. Applied in the gas phase, ozone also has found applications in odour and mold control and the storage and packaging of harvested agricultural products and processed foods. When applied, ozone decomposes, returning to the oxygen from which it was made, leaving no chemical residues from the antimicrobial agent on the food products. Monitoring is important because:
- Ozone is simultaneously a strong disinfectant as well as a strong oxidant so the indiscriminate overuse of ozone can cause oxidative damage to the food products
- Worker health & safety
Ozone for Treating Water
Food processing plant water can come from various sources including, from a municipality, river or lake. If the water has not been treated, then ozone can be of great assistance. The necessary application rates must be determined according to the impurities present in the influent water. For surface waters, ozone can aid the action of flocculating clays as well as chemical compounds. Filtration can be aided by oxidation of dissolved organic compounds, thus increasing filter run times to backwashing. Ozone can also serve as a disinfectant as the treated water enters the food processing plant.
Ozone for Process Water Recycle & Reuse
For proper treatment of process waters for reuse, attention must be paid to the materials now contained by the process waters. The process water to be recycled and reused should be treated by appropriate procedures, which can include one or more of the following treatment steps: flocculating agents (as necessary to assist removal of organic contaminants and colloidal materials), sedimentation, dissolved air flotation (DAF), filtration, treatment (with ozone) prior to recycling, etc. A significant advantage of ozone is that it saturates the water being treated with oxygen, giving the ozone-treated water a higher optical transmittance.
Ozone for Waste Water Treatment & Disposal
Waste waters from food processing plants usually contain high levels of organic contaminants. These usually are easily biodegradable and as such are amenable to biological waste water treatment. However, this type of treatment requires rather large land areas and time (~ 30 days or more) for completion. Biological treatment is the least costly method of waste water treatment, requiring the least amount of added energy from the food processor. When land is not available, or there is insufficient time for bioprocessing, ozone can provide a technology to reduce BOD and COD levels. Ozone has been shown to aid sludge dewatering, thus aiding filtration. Biotreated effluents can be disinfected with ozone, thus avoiding disinfection with chlorine, and also avoiding the formation of chlorinated organics that pass into the environment and enter the food chain.
Ozone for Washing Foods – Whole or Cut
For this application, water must be very clean and free of organisms. Usually this is not an application for recycled water. However, because of the oxidative properties of ozone, many organic contaminants of food wash waters are destroyed by ozone, allowing the wash water to be used for a longer period of time before disposal. Ozonated wash water for fresh cut salad mixes can later be sent for recycling. Meanwhile, ozone-washed salad mixes can be washed with chlorinated water. It is possible to reduce water use, chlorine use and plant waste water effluent volume simultaneously, resulting in significant cost savings.
Ozone for Storage of Raw Food Products
Based on prior research, water for this application is treated with ozone to a level appropriate for the specific food. Foods are washed, and then packaged (sometimes allowing exposure to air, others not). Many times, raw food products are stored in an atmosphere containing gaseous ozone. In these cases, it is important to know the concentrations of ozone necessary to protect the food product(s) from damage.
Foods normally are cleaned, then packaged. Chilean grapes, for example, are washed with water containing ozone (to lower contamination effects from Rhizopus stolonifer), then packaged in air-breathing plastic bags. Carrots are stored in air-breathing bags in ozone-containing atmospheres. However, when finally packed for distribution, carrots sometimes are packaged in sealed plastic bags. Specific types of packaging are required for specific foods. When packaging is to be in air-tight sealed plastic bags, ozone treatment can be followed by carbon dioxide and/or nitrogen. Ozone disinfects surface microorganisms, then the inert gases flush away any remaining oxygen that may allow growth of detrimental organisms.
Ozone for Treating Process Room Air
If workers are not present in a food processing room (rare circumstances – such as a storage room), ozone can be applied throughout the room air to levels that are effective for their intended purposes, but which may exceed federal government regulations for ozone in air. When workers are present, room air should be treated with levels of ozone that are below federal regulations, and these may be too low to accomplish their air-treatment objective. In these cases, contaminated air can be removed from the room, treated with appropriate quantities of ozone, excess ozone destroyed, and the cleaned air then returned to the processing room. Another approach is to mount ozone-generating UV lamps in the processing room ceiling. When turned on, these lamps produce lower concentrations of ozone than by the corona discharge technique used for treating large quantities of water. Since ozone gas is slightly heavier than air, it will fall from the ceiling UV bulbs to the floor of the processing room. Depending on the degree of odours present (ex. a garlic processing room) the odorants normally rise upwards, where they can encounter the descending ozone gas and be destroyed. At two meters above floor level, there may be no ozone at all (as measured by a wall-mounted ozone monitor pre-set at just below the appropriate OSHA level).
Still another approach is to install an ozone generator in ceiling corners and have each generator fitted with a timer. During times of human occupancy, the ozone generators are turned off. When the plant closes for the night, the timers automatically turn on the ozone generators, and then turn them off an hour or so prior to human occupancy. Gaseous ozone usually dissipates within an hour. To be sure there is no ozone above federal levels when workers return; a fan can be turned on a few minutes before workers return to exhaust the last traces of ozone from the processing room. This approach is not practical for heavy odours, or odours that develop quickly during processing. For mild odours, this procedure is a simple solution. This treatment also can greatly reduce the level of airborne mould in process room air.
Another application for ozone is in controlled atmosphere rooms in which stone fruit or apples typically are stored. These are large rooms used to preserve fruit harvested in summer/fall so they can be sold during winter/spring, after summer stocks are gone and prices are higher. In these storage rooms, negative pressures are used, along with nitrogen gas flooding, cold temperatures (35 °F) plus a slight residual of ozone for mold and mildew control.
For Plant Wash Down & Cleaning
Many ozone equipment suppliers offer specially designed “ozone-wash carts” that are portable and produce a pressurized water stream that contains a few parts per million of ozone dissolved in water. The solution is under pressure, thus the aqueous stream can perform the normal water wash down functions. However, because of the presence of dissolved ozone, wherever the aqueous spray contacts a surface, microorganisms on that surface will be attacked by ozone.
A special modification of this application for ozone is the washing of workers’ boots and waterproof aprons, when leaving the processing room for the day. Boots are hung on special racks outside the food processing room, and these are rinsed with ozone-containing water from the portable ozone-water-washer.
Ozone washes can replace Best Management Practice washing procedures that utilize strong sanitizers. They are usually used when a quick wash down is needed during break periods and shift changes. The ozonated water does not adversely affect products left in conveyors and on cutting tables. These same products sprayed with chlorine- and/or peroxide-containing sanitizers would need to be discarded. Ozone washes can clean many food and container surfaces; however, they do not provide residual microbial protection.
As much as 30 percent of all produce shipments are in some way adversely affected by microbial contamination before reaching the consumer. This statistic does not account for potential loss from over-ripening, as well as the fact that organic food is even more at risk because of the absence of traditional chemicals such as fungicides. The use of ozone technology, coupled with load protection monitoring, can reduce the risk of losses, enhance food safety, and ensure higher-quality arrivals by maintaining post-harvest freshness throughout long distance voyages.
Ozone is used to kill decay and disease-causing molds, yeasts, bacteria, and viruses in the air, and on surfaces, as well as to consume and regulate ethylene levels. Certified organic and approved by the USDA and the FDA, ozone acts as a powerful, residue-free disinfectant that immediately reverts back to oxygen, leaving the product’s taste, texture, and smell characteristics in their natural state. For shipping fresh produce around the globe, ozone can extend freshness, minimize decay, and reduce pathogens without the use of chemicals. Sophisticated sensing, communications, monitoring, alerting, and reporting of all of the critical variables such as T, RH, O2, CO2, O3, time, location & power can ensure the safe, fresh arrival of food and help to continuously improve the efficiency in which safe, fresh food gets delivered to the market.
“The ability of the Series 500 to produce reliable and repeatable ozone readings takes the guesswork out of installations, and boosts the engineer’s and customer’s confidence”Geoff Allum: Exoair