Disinfectant types

Chemical disinfectants are defined by their mode of action and can be broadly split into two groups, oxidising and non-oxidising.

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Oxidising disinfectants such as Sodium Hypochlorite, Peracetic Acid and Hydrogen Peroxide attack all cellular material and stop the micro-organism from functioning. Unfortunately they will also attack any food soiling residues, this will essentially neutralise the disinfectant and reduce its efficacy.


Non-oxidising disinfectantsi such as Quaternary Ammonium Compounds (QACs) are more subtle in their operation.  They penetrate the cell wall and disturb the phospho-lipid molecules which make up the cell membrane; they then block metabolic pathways needed for the organism to survive and /or cause it to leak vital chemicals.

Sodium Hypochlorite

Sodium hypochlorite is very effective against all types of micro-organism (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 also 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.

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Hydrogen Peroxide

Hydrogen Peroxide works in the same manner as Sodium Hypochlorite but may not be as effective against as many micro-organisms. It is used predominantly in the beverage and brewing sectors, as it is low foaming and ideal for Clean In Place systems.  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

Peracetic acid (PAA) products are used mainly in the 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 Peracetic Acid 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.

Non-Oxidising Disinfectants:

 

Quaternary Ammonium Compounds (QAC’s or quats)

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.

Alcohols

Where there is a requirement for light cleaning and disinfection in an essentially ‘dry’ area, such as a Bakery, then the use of an alcohol based spray/wipe product becomes very useful.  This is typically a blend of alcohol, QAC and possibly mild detergent additives formulated to provide good disinfection in lightly soiled conditions therefore reducing the amount of water used.  The product flashes dry after application, thus removing the need for an undesirable wipe-dry operation. 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. Alcohol disinfectants have also been adapted for use a post wash hand disinfectant. 60 to 70% Alcohols are fast acting.

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Effects of Time & Concentration

Contact time and concentration are two of the most vital factors that can affect the performance of a terminal disinfectant.  Although some disinfectants are effective within minutes, in most cases it is recommended that they receive at least 15-20 minutes contact time.  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 vital. Attention should be paid when applying disinfectants to horizontal surfaces after rinsing; the presence of pools of water will dilute the disinfectant solution.