Disinfection is the reduction, by means of chemical agents and/or physical methods, of the number of microorganisms in the environment, to a level that does not compromise food safety or suitability. (Codex)
Sterilisation is the process of killing all forms of microbial life including fungi, viruses, bacterial spores and vegetative bacteria.
Disinfection in the food and food service markets is used to control microorganisms that can cause harm to the consumer of the food product by pathogens such as Listeria spp., Salmonella spp. and E. coli. or, cause the food to spoil, reducing its shelf-life and potentially making it un-wholesome through organisms such as Pseudomonas spp. or Clostridium estertheticum.
Disinfection is primarily undertaken for pathogen control, particularly in high risk or high care areas but is also often undertaken in low-risk areas for the control of spoilage microorganisms.
Disinfection is not applicable to all surfaces in a food manufacturing environment and should only be used on those surfaces where the presence of significant numbers of microorganisms will have an adverse effect on the safety and quality of the food handled. If disinfection is deemed to be necessary, then the following areas should be considered:
The following factors should be considered when choosing a disinfectant:
Spray disinfection is the most common method for applying disinfectant to surfaces. It is versatile, gives good coverage and is an economic means of applying disinfectant solution. It can be carried out by using a variety of different applicators. The most common are: small trigger sprayers, pump-up sprayers, compressed air driven sprayers, or via a high pressure washdown system using a high pressure injector or via a medium pressure system.
It is important to consider the risk of liquid pooling. Poor equipment hygienic design features such as dead legs in closed processing systems, or undrainable areas of open processing equipment, may cause disinfectant solutions to pool. Such pooling could result in subsequent food products being subjected to high volumes of disinfectant which may enhance food adsorption of disinfectants.
Surfaces should be free of pooling water prior to disinfectant application to prevent the dilution of disinfectants to a sub-lethal dose.
This is probably the most effective means of disinfection as the item to be disinfected is fully immersed in the disinfectant solution, giving good contact time to all surfaces. It is important that items are effectively rinsed before submerging them into disinfectant as detergent residues or debris will inactivate the disinfectant.
It is also important that the disinfectant solution is changed regularly based on a risk assessment and ideally disinfectant soak vessels should be covered to protect from cross contamination.
This type of disinfection method is usually confined to small items such as utensils, knives, blades, small machinery parts, cutting boards etc.
Hot water or steam recirculation in closed systems can be an effective method of disinfection. However, it is very difficult to achieve on large items of open equipment in a food manufacturing operation so in the vast majority of circumstances chemical disinfection is the preferred method.
Steam disinfection of surfaces via a lance has had some success in certain environments but care should be taken as the steam can have an adverse effect on some plastics, paint and machinery and lubricants/grease and also pose a safety hazard.
Some manufacturers have had great success with enclosed steam heating of large open equipment when covered with large plastic bags and heat treated at 70°C plus for > 2 minutes. This has proven successful in destroying Listeria spp. Engineering management should always be consulted before considering this method of thermal disinfection.
The basic physical methods available for the disinfection of air, water, and surfaces are filtration, exposure to ultraviolet radiation, photocatalysis, cold plasma, electric discharges, and electroporation in an electric field.
Physical disinfection via UV light, ionisation and cold plasma, are very rare in the food industry and used for very specific applications.
UV light is the most practical but is only applicable to clean smooth surfaces that do not allow microorganisms to be shadowed from the light.
