During manufacture, food can be exposed to microbiological cross-contamination from surfaces and the air, which can cause food spoilage and safety issues. The traditional approach to controlling such contamination has been to target specific sites within the manufacturing environment with cleaning and disinfection regimes.
The primary focus of the regimes is typically on food production equipment, with much of the rest of the processing area not receiving routine decontamination. This targeted approach may be sufficient for day to day control, but doesn’t necessarily eliminate all of the organisms responsible for contamination. In some instances, microbial strains have become persistent in food factories, surviving for several years.
Previous research at Campden BRI assessed the microbial flora of the high-risk areas of five chilled food factories, all operating good practice cleaning and disinfection regimes, and identified persistent strains of listeria spp. and Escherichia coli that had remained in the processing environment in excess of three years. Clearly, these ever-present organisms represent a constant risk to product safety, which could be compromised if there was any loss of hygiene control in these factories.
The need for further reduction of pathogens and the identification of persistent strains within the factory environment has led to a significant increase in the use of novel whole room disinfection techniques to supplement routine cleaning and disinfection.
The pharmaceutical and clinical sectors have been targeted by a range of whole room type decontamination systems, but these techniques have had little microbiological assessment and their practical operation and benefit in the food and drink industry is relatively unknown. The Campden BRI Review addresses the practical use, safety and efficacy of some of the latest developments in this area.
The range of techniques designed for whole room disinfection is increasing but those that are commercially available include:
The critical factors to address before using these techniques include: identifying areas where the decontamination processes can be applied, any health and safety issues related to using the technique and the practical considerations related to their use in the food processing environment.
There’s also a need to understand how often a whole room disinfection method will be used in the production area. The techniques can be used on a daily basis, after the routine cleaning and disinfection procedure has been implemented, or as seen in some factory environments, these techniques can be used daily to replace the terminal disinfection step.
There’s also the option to use a whole room disinfection technique as part of the periodic cleaning and disinfection procedures that occur monthly, quarterly or annually or it may only be used for decontaminating an area after a pathogen contamination incident.
The level of disinfection that the whole room disinfection systems can achieve also needs to be determined, as some may achieve decontamination of all exposed room surfaces, such as ceilings, walls, floors and food processing equipment, but others may include some penetration into equipment to contact indirectly exposed surfaces. They may also provide disinfection of the air in the area being treated. The advantage to using these techniques is that for some, the decontamination process can be certified, providing documented evidence that the procedure has taken place.
Two examples of whole room disinfection techniques are fogging and ozone.
Applying chemical disinfectants to production areas as fogs or mists is a method that has been used routinely in the food industry to control cross contamination. The purpose of fogging a production area is to create and disperse a disinfectant aerosol to reduce the numbers of airborne microorganisms and also to apply disinfectant to surfaces that are not routinely disinfected and that may be difficult to reach, such as overhead surfaces.
Fogging is done by using either a static, purpose-built system in an area of a factory with strategically placed nozzles, or more commonly by using a mobile unit. The equipment works by supersaturating the atmosphere with a fog of disinfectant chemical; the area that can be covered will vary depending on the application system being used. A built-in system will typically be used for production areas larger than 200m³, with mobile units usually being employed for areas smaller than 200m³.
For whole room disinfection, fogging is only effective if sufficient chemical is deposited onto all of the food contact and environmental surfaces. Providing a suitable disinfectant is used, research has suggested that fogging is effective at reducing airborne microbial populations by two to three log orders in 30 to 60 minutes and horizontal surfaces up to six log orders in 60 minutes, with minimal effect on vertical surfaces and the underneath of equipment.
Therefore, the technique tends to be used as an additional safeguard to the routine cleaning and disinfection procedure. Chemical fogging can, however, be improved with the use of electrostatic fogging nozzles, which help ensure a greater surface coverage of the aerosol droplets, even on non-horizontal surfaces.
Ozone has been used for decades for water treatment, as it inactivates a wide range of microorganisms through oxidation, but the benefit of using ozone in the food industry ?is that it’s environmentally friendly, with any residual ozone spontaneously decomposing to oxygen.
Due to its reactive, unstable nature, ozone is produced at the point of use. Ozone generators effectively pass air through a high-energy source within the equipment and the resulting physicochemical reaction leads to the formation of ozone that can be used for area or surface decontamination.
A typical ozone decontamination cycle consists of three phases in a one step process:
Cycle times vary depending on the area volume, desired level of decontamination and area contents, but are typically between 30 and 90 minutes.
Vapours and gases have several advantages as they can effectively penetrate every part of a room, including sites that might prove difficult to gain access to with conventional liquids and manual disinfection procedures.
More information on the use, advantages and disadvantages of chemical fogging, ozone and the other whole room disinfection techniques can be found in the Campden BRI Review 63: Whole room disinfection – a review of current methods.
Karen Middleton is research manager of the food hygiene department and Tim Hutton is publications manager, both at Campden BRI, an organisation that carries out research and development for the food and drinks industry.
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