Disinfection questions answered

A number of common questions are asked in relation to disinfection routines. These include:

What are the effects of time and concentration? 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 five minutes contact time for bacteria and 15 minutes for yeast and mould. 

Additional contact time will help provide a performance safety factor in the event of the disinfectant being applied to a very wet surface and dilution takes place, or where soiling is still present, and some deactivation of the disinfectant may occur.

Failure to allow the recommended contact time could result in an ineffective reduction of micro-organisms on the disinfected surface, so disinfectants should always be used at the manufacturer’s recommended concentration and an even coverage of the surface is important.

Should disinfectants be rinsed or left to drain/dry? 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 Quaternary ammonium compounds (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 Europe 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, it provides protection to food contact surfaces, so in the event of being 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.

 

Can I leave a disinfectant on a surface prior to organic production? When producing foodstuffs 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.

 

Will residual disinfectant taint foodstuffs? 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.

 

Will residual disinfectant damage equipment? Formulations should not cause damage to equipment. Most disinfectants used in the UK food industry are manufactured by companies that specialise in offering solutions for this sector. However, it is always advisable to check product data sheets for compatibility, particularly if equipment contains soft metals such as aluminium or copper.

 

Can organisms become resistant to biocides? 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.  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).

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 it is recommended you rotate a non-oxidative biocide (QAC, Triamine, Amphoteric) with an oxidative biocide (Hypochlorous, PAA etc.).