Disinfection is the destruction of micro-organisms by either chemical or physical methods. It is part of the whole cleaning regime which is designed to reduce the level of microbial contamination in foods to an acceptable level; i.e. a level which does not pose any risks to health or to the quality of product.
In contrast Sterilisation is the complete destruction of all micro-organisms leaving surfaces free of any microbial contamination.
Disinfection can be achieved in a number of ways; such as:
Thermal disinfection can be used to achieve disinfection, pasteurisation or sterilisation – Cooking is a form of disinfection reducing the bacterial loading on the food to a safe level.
Irradiation either as UV or gamma ray can be used – UV treatment of water will help to control bacterial levels and irradiation of foods where food is treated with very low levels of ionizing radiation.
Filtration – Water and air can be passed through very fine filters to remove debris and bacteria. Beer filtration is an example of this where filtration can be used to remove brewing yeast prior to bottling or canning.
Gas & Vapours – Poultry growing sheds and silos can be treated with gaseous disinfectants such as formaldehyde. Ozone, chlorine dioxide and hydrogen peroxide can be used for whole room disinfection.
Liquid – Chemical disinfection is commonly used for the disinfection of surfaces, equipment and airspace.
If the disinfection part of a cleaning process is to be effective, it is vital that the surface to be disinfected is free of food soil or chemical residues. The presence of any of these may affect the disinfectant and prevent it from working effectively.
Effective cleaning will typically remove approx 99.9% (3log reduction) of the bacteria on a surface but there may be considerable numbers still present. This is why the disinfection stage is required to help bring the bacterial numbers down to an acceptable level >99.999% (>5log reduction).
Biofilms
A biofilm consists of microbes and extracellular products in association with a surface. This medium consists largely of water (98-99%) and various polymers, commonly polysaccharides and glycoproteins. The micro organisms are not uniformly distributed throughout the biofilm as the biofilm consist of micro-colonies with channels in between.
Biofilm development has been found to be time dependent with bacterial colonies possibly developing into biofilms given sufficient time and nutrients. The most common species that have been found within biofilms have been pseudomonad, coliforms and staphylococci.
Bacteria can gain a number of advantages when protected by a biofilm such as resistance to preservatives, disinfectants, antibiotics, biocides and heat. Biofilms therefore constitute a reservoir of many different species able to resist environmental fluctuations.
Biofilms protect micro organisms from being washed away in the product flow, from cleaning and disinfection and in sites that dry out, desiccation. Research has found that biofilm organisms can be up to 100 times more resistant to disinfectants commonly used in the food industry.
Biofilms are effectively removed using high shear forces (brushing, padding and high pressure cleaning) in combination with a chlorinated alkali detergent.
Spray Disinfection
Spray disinfection is the most common method for applying disinfectant to surfaces. It is versatile, gives good coverage and economic on use of disinfectant solution.
It can be carried out by using a variety of different applicators. The most common are: Small trigger sprayers, pump-up sprayers, sprayers that operate using compressed air. They can also be applied via wash-down systems at high, medium or low pressures.
Soak Disinfection
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. This type of disinfection is usually confined to small items such as utensils, knives, blades, small machinery parts, cutting boards etc. that are capable of being submerged.
Aerial Disinfection or Fogging
Aerial Disinfection is used primarily for disinfecting airspace in production and processing areas. As micro organisms can be carried in the air and transferred to food contact surfaces it may be important, particularly in high care environments, to disinfect the airspace.
Fogging should only be conducted after all cleaning and disinfection of food contact surfaces has taken place. It should never be used as an alternative to surface disinfection.
It can be carried out using a gas, such as ozone, or more usually with a 1-3% disinfectant solution via a compressed air fogging unit. The liquid foggers work by supersaturating the atmosphere with a disinfectant fog. The area they can cover and penetrate will vary dependent on the size of the atomised particle. Although fogging is intended for disinfection of airspace, some research has been conducted to determine if it can be used as a method for terminal disinfection of all critical surfaces in a food processing environment. This method is called electrostatic fogging where surfaces are electrically charged to attract the disinfectant droplets to the surface. If this approach could be made to work, then considerable benefits may be brought to the cleaning and disinfection of food premises.
Vaporisation
Vaporisation of certain disinfectants is used as a method for whole room disinfection; for instance: vaporised hydrogen peroxide.