Food safety

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.

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.