In generalQACsare effectiveagainst vegetativebacteriabut havegreatest
effectiveness against Gram-positive bacteria. Yeast and moulds can be
inactivated to some extent but higher concentrations are necessary (Krop,
1990;Bernstein, 1990)(see Table4.2).QACsare mosteffectivein the rangeof
pH 6 and 10 (Beuchat, 1998), which limits their applicability in acid
environments.
Modeof action
The principalactionsof QACsare loweringof surfacetension, inactivation of
enzymesand denaturation of cell proteins.As a result of adsorptionof QACs
ontothe microorganism's surface, the cell'spermeabilityis changed dramatic-
ally.Thisresults in leakage of intracellularlow-molecularcompounds,degrada-
tionof proteinsand nucleicacids,and cell walllysisby autolyticenzymes
(McDonnell and Russell,1999).The concentration applieddepends on the type
of microorganisms present in the product, the processing system and the
environment. Concentrationstypically used are in the rangebetween 150 and
250 mg lˇ^1 of activeQuaternary Ammonium (QA)(Bernstein,1990; Beuchat,
1998).Allerberger and Dierich(1988)showeda bactericidaleffect onE. coliat
a concentrationof 100 mg lˇ^1. Lowconcentrations(0.0005% w/v = 5 mg lˇ^1 ) of
benzalkonium chloride are sporostatic, inhibiting outgrowth but not
germination.QACs are not sporicidal (Russell, 1990).
4.2.3 Peroxygens
Hydrogenperoxide and peracetic acid are the mainrepresentativesof the group
of peroxygens. Hydrogenperoxideis widelyapplied withinthe foodindustry
and is commerciallyavailablein concentrationsvaryingbetween3% and 90%
w/v,with35%routinely usedin the foodindustry (McDonnellet al., 2002).It is
Table4.2 Efficacyof quaternaryammoniumcompoundson differentinfectiousagents
Infectiousagent Efficacy Comments Source
Bacteria Russell(1995)
Gram-positive á
Gram-negative á MIChigherthanGram+
Spores ˇ Sporostatic Russell(1990)
Viruses Quinnand Markey
Lipid á (1999)
Smallnon-lipid ˇ
Non-lipid á=ˇ
Mycobacteria ˇ Russell(1996)
Yeast/moulds á Mouldsmoreresistant Russell(1999c)
á, effective,ˇineffective,á=ˇ, limitedefficacy
Pathogen resistanceto sanitisers 73