A wide range of disinfectant products are available, which vary in terms of their active ingredients, how they can be applied and their intended use.
The mechanisms of action are not always completely known and continue to be investigated. A range of different factors needs to be considered as part of the process of selection including the mode of action, efficacy, compatibility, cost and with reference to current health and safety standards.
A disinfectant must have a wide spectrum of activity. This refers to the ability of the disinfectant to kill micro-organisms of varying types and in different physiological states.
Is there a requirement for the disinfectant to be sporicidal? This requirement influences the type of disinfectant purchased. Sporicidial disinfectants tend to have greater health and safety considerations and some, particularly chlorine-based disinfectants, are aggressive to certain types of surfaces and will cause discolouration and abrasion.
The disinfectants must meet the requirements of the validation standards to measure bactericidal, fungicidal and, if appropriate, sporicidal and virucidal activity.
The disinfectant must be rapid in action with an ideal contact time of less than 15 min. The contact time is the time taken for the disinfectant to bind to the micro-organism, traverse the cell wall and membrane and to reach its specific target site. The longer the contact time, then the longer the surface or article needs to be left, prior to reuse.
Some disinfectants require certain temperature and pH ranges to function correctly. One type of disinfectant, for example, may not be effective in a coldroom due to the lower temperature. The reason for this is that the validation standards for disinfectants measure the bactericidal activity at 20°C and therefore the disinfectant may not be as effective at higher or lower temperatures.
Prior to the use of disinfectants it is essential that as much dirt and soil is removed as possible. This requires the application of a detergent. Some disinfectants are not compatible with certain detergents. In such instances, detergent residues could neutralise the active ingredient in the disinfectant. Any disinfectant purchased should be compatible with the detergent used.
Different disinfectants are not compatible with all types of surfaces. The disinfectants must not damage the material to which they are applied (although it is recognised that repeated applications over several years may cause some corrosion). For more aggressive disinfectants, a wipe down using water or a less aggressive disinfectant such as an alcohol is sometimes necessary to remove the residues. In addition to some disinfectants having a corrosive effect, others may be absorbed by fabrics, rubber etc, which lessens their bactericidal properties.
The cost of the disinfectant is also a factor to consider, especially if it is to be used over a large surface area.
The presentation of the disinfectant is an important choice, whether as a pre-diluted preparation in a trigger spray or as a ready-to-use concentrate or an impregnated wipe.
The disinfectants must be safe to use, in terms of health and safety standards. Here, the main concern is with operator welfare. A related concern is the impact upon the environment.
Contact time and concentration are two important factors that can affect the performance of a disinfectant. Although some disinfectants are effective within minutes, in most cases it is recommended that they receive at least 5 minutes contact time for bacteria and 15 minutes for yeast and mould.
Additional contact time helps provides a performance safety factor in case the disinfectant is applied to a very wet surface and dilution takes place, or where soiling is still present, and some deactivation of the disinfectant takes place.
Failure to allow the recommended contact time could result in an ineffective reduction of micro-organisms on the disinfected surface. Disinfectants should always be used at the manufacturer’s recommended concentration and an even coverage of the surface is important.
This will depend on the type of disinfectant used. In general, hypochlorite based disinfectants should be rinsed to remove the taint potential.
With peracetic acid and hydrogen peroxide based products, rinsing is often not necessary but a risk assessment and taint tests will need to be carried out.
With QAC and Triamine based products, it has been traditional in the UK and Ireland to not rinse. Food businesses must comply with regulation (EC) No 396/2005 on maximum residual levels of QAC. The UK and Irish food manufacturing sector, particularly the chilled ready-to-eat sector, are unusual in the European Union due to not rinsing off food contact surfaces prior to production recommencing, increasing the risk of QAC levels being in excess of the proposed 0.1mg/I MRL.
Complying with the regulation can be done via validation of the process to ensure food is below the MRL required levels, rinsing food contact surfaces to remove the QAC disinfectant or changing to a non-QAC disinfectant.
There are strong technical reasons to leave a disinfectant on a surface after cleaning. Firstly, they provide a protective challenge to food contact surfaces, such that if the surface is subsequently cross contaminated by pathogenic or spoilage microorganisms, the disinfectant residue will provide a biocidal action. Secondly, there is often insufficient time for process lines and the environment to dry prior to production commencing. Thirdly, holding cleaned utensils and small items of equipment in disinfectant soak baths allows penetration of disinfectant into surface features and preserves their low microbial surface count prior to subsequent reuse.
When producing food stuffs to organic status it is essential, that after leaving disinfectant for sufficient time to be effective, all residues are rinsed away with potable quality water before production commences. The only exception to this is when pure alcohols are used for disinfection; these will evaporate to leave no residues.
Disinfectants supplied by reputable manufacturers are independently assessed for taint potential using well recognised tests, generally conducted blind using a panel of ‘tasters’. Tests are conducted using high fat materials that are impregnated with disinfectant, due to fatty materials being most likely to absorb taint elements.
Products supplied by Kersia have all been taint tested by Campden BRI, with copies of the reports available on request.
Great care is taken to ensure that formulations do not cause damage to equipment with most disinfectants used in the UK food industry manufactured by companies who specialise in the food industry. However, it is advisable to always check product data sheets for compatibility, particularly if equipment contains soft metals such as aluminium, copper.
Many bacteria have the ability to tolerate low levels of disinfectants, particularly non-oxidative QAC’s and Triamines, by actively pumping them out of their cells. For example, a cell expressing efflux pumps could tolerate approximately 30ppm of QAC whilst one not expressing efflux pumps could tolerate 5-10 ppm. Note: Typical use concentrations of QACs and Triamines in formulated products are around 500 to 1000 ppm (active material delivered at circa. 1% v/v product).
We have been using much the same disinfectants at pretty much the same concentrations, for >50 years. During this time the industry has verified the performance of the cleaning and disinfection programme via environmental sampling, for both TVC and specific pathogens. There is no evidence in that time that either: general micro levels are any higher on surfaces after cleaning and disinfection or specific disinfectant resistant strains have evolved.
Provided disinfectants have passed the relevant EN tests (1276, 1650 and 13697), there is no need to rotate between properly formulated disinfectants that are used at the correct concentration and contact time. If rotation is specified then you need to rotate a non-oxidative biocide (QAC, Triamine, Amphoteric) with an oxidative biocide (Hypochlorous, PAA etc.).
