activeconcentrationor/andofferingsomeprotection to the microorganisms.
Indeedthe antimicrobialefficacy of somebiocidescan be deeplyaffectedby
soiling(Table 38.1).Practical testsnowreflect the importanceof soiling by
stipulating testing undercleanand dirtyconditions,usually by the addition of
serumalbumin (e.g.3 g Lˇ^1 for testingunderdirtycondition)in the reaction
vessel (e.g. CEN1276, 1997a). The effect of soiling also emphasises the
necessity of cleaningsurfacesand equipment beforea biocidal productis used,
or combininga disinfectantwitha detergent.In the foodand dairyindustry, a
reduction in biocidal activitymay occurwiththe presenceof organic matter and
effectivepre-cleaning prior to disinfectionis recommended. Somechemical
biocides mayexerta detergent action, whereassome detergents exhibitsome
biocidal activity. In this respectthe surfaceto be treatedis importantto consider
(see below) as it affects the efficacy of a biocide or biocide/detergent
combination.
The activityof biocides usuallyincreases witha rise in temperatureand this
principle is used, when combining biocide and steam sterilisation. Other
equipment, suchas someautomated washerdisinfectors, also combinebiocides
and elevatedtemperature.On the otherhand,low temperature maydecreasethe
antimicrobialefficacy of biocides. Temperatureis particularlyan issue during
storageof a biocidalformulation/product, especiallyuponpreservation, and
wherechilled foodis produced (Tayloret al., 1999).The effectof temperature
on activity can be calculatedwiththe temperaturecoefficient () and more
Table38.4 Examplesof concentrationexponent()
Biocide Exponent
Phenolics 4±9.9
Alcohol
Benzylalcohol 2.6±4.6
Aliphaticalcohols 6.0±12.7
Cationicbiocides
Chlorhexidine 2
Polymericbiguanides 1.5±1.6
QACs 0.8±2.5
Crystalviolet 0.9
Aldehydes
Formaldehyde 1
Glutaraldehyde 1
Peroxygens
Hydrogenperoxide 0.5
Metallicsalts
Silvernitrate 0.9±1.0
Mercurials 0.03±3.0
Organicacid
Parabens 2.5
Sorbicacid 2.6±3.2
Potassiumlaurate 2.3
Testingthe effectivenessof disinfectants and sanitisers 647