This Q&A section addresses some frequently asked questions about a commonly misunderstood topic.
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 microorganisms 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 peracteic 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 as 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.).
