Chemical disinfectants are defined by their mode of action and can be broadly split into two groups, oxidising and non-oxidising.
Oxidising disinfectants such as Sodium Hypochlorite, Peracetic Acid and Hydrogen Peroxide attack all cellular material and stop the microorganism from functioning.
Unfortunately, they will also attack, and be consumed by, any food soiling residues thereby reducing the disinfectant efficacy.
Sodium hypochlorite is very effective against all types of microorganisms (including spores). It is inexpensive in comparison to other disinfectants and it is unaffected by hard water. The efficacy of a solution is dependent on its pH.
Care should be taken with storage and stock rotation of sodium hypochlorite. The product will naturally lose available chlorine (by conversion to sodium chloride – not chlorine gas) and should generally be used within 3 months of manufacture. If stored in direct sunlight the rate of loss of available chlorine increases. It should also be stored separate from other chemicals, particularly acids, as lethal chlorine gas will be released if these two products are mixed.
Ideally, sodium hypochlorite should be automatically dosed via a chlorine compatible dosing unit to ensure that it is used at the correct strength.
Chlorine dioxide is mainly used for the disinfection of water systems but is also being utilised for surface disinfection in CIP. It is produced by mixing under controlled conditions:
All the above methods must be carried out using specialised dosing systems with safety precautions built in. The main advantages that chlorine dioxide has as a disinfectant are: broad spectrum of activity at low concentrations, rapid microbiological killing action, dosing is reliably and automatically controlled, it does not readily react with organics to form ecotoxic and bio accumulative by-products and it is much less tainting than chlorine.
It is approved for potable water use (0.5mg/l causes no objectionable taste, whereas the same concentration of chlorine would). It will typically be used at 0.3mg/l in water treatment and at 5 to 15 mg/l (ppm) for surface disinfection.
Hydrogen peroxide works in the same manner as sodium hypochlorite but is not as broad spectrum. It is used predominantly in the beverage sector for disinfection of product packs prior to aseptic filling.
Typically, a 0.03% solution will give 100 ppm hydrogen peroxide, at this level of concentration it may not require rinsing from the surface. Used at elevated temperatures, hydrogen peroxide becomes more effective. It is not safe to use on aluminium, zinc, tin or their alloys.
Peracetic acid (PAA) products are used mainly in the dairy, beverage and brewing sectors as they are low foaming, effective against all types of bacteria and can be used at very low concentrations and temperatures. Typically, two concentrations are commercially available; these have activities of 5% and 15% peracetic acid.
Used at the recommended concentration (e.g. 0.1 - 0.4%) a 5% active product will give 50-200 ppm PAA which would not typically be rinsed off but allowed to slowly decompose to acetic acid, oxygen and water.
As with other oxidising disinfectants PAA should not be used on soft metals. Some PAA formulations are approved by DEFRA for use against specific animal diseases.
Iodophors are expensive but incredibly effective disinfectants having both detergent and disinfectant properties. They are produced by dissolving iodine in an acid medium together with surfactants. Iodophors have several advantages including: The ability to kill a wide range of organisms at low temperatures, short contact time and the ability to cope with soiling/hard water.
Iodophors are now only approved for agricultural applications such as farm gate foot baths and drive-over disinfectant blankets and have DEFRA approvals for many farm based diseases.
Non-oxidising disinfectants such as Quaternary Ammonium Compounds (QAC’s), Biguanides and Triamines are more subtle in their operation, with a different number of modes of action depending on the biocide and organism.
QAC based disinfectants, with low toxicity and low taint, have been the mainstay for the food processing industry for 20 years. QAC’s (or Quats) are the most widely used biocides in food or beverage businesses. Properly formulated products are effective against gram positive bacteria and against gram negative bacteria, but less effective against spores, moulds and fungi.
QAC based disinfectants are stable and generally taint free. They may be inactivated by hard water, organic material and some plastics. To improve the effectiveness of QACs, formulations often include sequestrants and non-ionic detergents.
The focus on the pesticides regulation in 2015 threw some challenges to the industry. A food business has a number of choices on how to comply with the regulation; these include validation of the process to ensure the food product is below the MRL for QAC, rinsing to remove the QAC disinfectant from food contact surfaces and/or a change to a non-QAC disinfectant.
Triamines are excellent disinfectants but can be expensive. They have low toxicity, relatively non-corrosive, tasteless, odourless and used at approx. 1%. Formulations often have similar co-formulants to QAC based products.
These are cationic bactericides similar in function to QAC’s. Products formulated with biguanides are not supplied by Kersia due to the Health Hazard classification of biguanide as a raw material.
Where there is a requirement for light cleaning and disinfection in an essentially ‘dry’ area, such as a bakery or for sensitive packaging or electronic equipment, then the use of alcohol based spray/wipe products becomes very useful.
These products are typically a blend of alcohol, QAC or triamine and possibly mild detergent additives formulated to provide good disinfection in lightly soiled conditions, therefore reducing the amount of water used. The product flash dries after application, thus removing the need for an undesirable wipe-dry operation. In these formulations water is still present, so care must be taken with electrical items.
Alcohol disinfectants have also been adapted for use as post hand wash disinfectants, at a concentration of 60 to 70% alcohol and these formulations are fast acting. Care must be taken because of the flammability of alcohols such as ethanol and iso-propanol, two of the alcohols commonly used in these products.
