Neutralisingagentsare particularly importantfor those biocides that interact
strongly withthe bacterialcell or withthosewitha low concentrationexponent.
However, it is importantto note that microorganismsthat havesuffereda certain
amountof damage following an antimicrobialtreatment mightnot be ableto
recoverevenwhena neutraliser is added.Furthermore, some neutralisersmight
increase the amount of damagealreadysustained by the microorganisms.
Biocideswitha highconcentrationexponent lose theiractivity rapidly upon
dilution(Section38.2.2). Although this mightbe sufficient to overcomeany
bacteriostatic activity, the effectof sub-inhibitory(residual) concentrationson
the bacterialcell remains poorlyunderstood(Maillard,2002). As mentioned
previously, the use of neutralisersmightdamage furtheralreadystressedmicro-
organisms (e.g. non-ionic surfactants, sodium thiosulphate, thioglycollate).
Assessing the toxicity of a neutralisingsolution (notably whenthe recommended
concentrationis changed) against all test microorganismsis of a paramount
importance. In addition, the efficacy of a neutralising solutionto quench
effectively an antimicrobial product against specific test strains and test
conditions must also be assessed, notably when severalneutraliserscan be used
Table38.7 Examplesof recommendedneutralisingsolutions(basedon CEN 1276
(1997a))
Numberof
components
Neutralisercomposition1 ∑ Phosphatebuffer(0.25mol Lˇ^1 )
∑ Freshegg yolk(0.5 or 5% v/v)
∑ Phospholipidemulsion(50 mg mLˇ^1 )
∑ Glycine(concentrationdependsuponthe product)
∑ Sodiumthioglycollate(0.5 or 5 g Lˇ^1 )
∑ L-cysteine(0.8 or 1.5 g Lˇ^1 )
∑ Sodiumthiosulphate(5 g Lˇ^1 )
∑ Thiomalicacid(0.075%v/v)
∑ Catalaseor peroxidase(for the inactivationof hydrogenperoxide)
2 ∑ Freshegg yolk(5% v/v),polysorbate80 (40 g Lˇ^1 )
∑ Ethyleneoxidecondensateof fattyalcohol(4% v/v),lecithin
(4 g Lˇ^1 )
∑ Polysorbate80 (30 g Lˇ^1 ), lecithin(3 g Lˇ^1 )
3 ∑ Polysorbate80 (30 g Lˇ^1 ), sodiumlaurylsulphate(4 g Lˇ^1 ), lecithin
(3 g Lˇ^1 )
∑ Ethyleneoxidecondensateof fattyalcohol(7% v/v),lecithin
(20 g Lˇ^1 ), polysorbate80 (4% v/v)
∑ Polysorbate80 (30 g Lˇ^1 ), lecithin(3 g Lˇ^1 ),L-histidine(1 g Lˇ^1 )
4 or more ∑ Polysorbate80 (30 g Lˇ^1 ), saponin(30 g Lˇ^1 ),L-histidine(1 g Lˇ^1 ),
L-cysteine(1 g Lˇ^1 )
∑ Lecithin(3 g Lˇ^1 ), polysorbate80 (30 g Lˇ^1 ), sodiumthiosulphate
(5 g Lˇ^1 ),L-histidine(1 g Lˇ^1 ), saponin(30 g Lˇ^1 )
Testingthe effectivenessof disinfectants and sanitisers 655