standardchlorinesolutions(sodiumhypochlorite)a concentrationof 3 mg lˇ^1
chlorine dioxidehas the sameinactivating effectonE. coliO157:H7andL.
monocytogenesas 200 mg lˇ^1 of chlorine whenappliedfor decontaminationof
fruitsurfaces(Rodgerset al., 2004).Iodine
Iodine is widelyusedfor sanitisingfoodprocessingequipment and surfaces.
Iodine is less reactive thanchlorine and less affectedby the presenceof organic
matter but also has disadvantages suchas staining humanskin,plastic partsof
equipment,and also has a relativelyhighpriceas compared with chlorine(Krop,
1990; Hugo and Russell, 1999). Solutions of 15% active chlorine are
commercially available for®0.20±0.30per kg whereas a 6% solutionof iodine
in 70%ethanolcostsapproximately®400 per kg (BoomChemicals). Iodine is
applied in three possible formulations:ethanol-iodine, aqueous iodinesolutions
and iodophores. The iodophoresare most frequentlyapplied and have high
solubilityin water, produce no vapour(below50 ÎC), are lesscorrosive to
stainlesssteelthanchlorine-containingsolutions, and are generally effective
against Gram-negativeand Gram-positive vegetative cells,yeasts,mouldsand
viruses (Bernstein, 1990 ; Beuchat,1998).Bacterial spores(B. cereus,B. subtilis
andC. botulinumtype) are moreresistant to iodophors(D-valuesare 10±100
times higher) and higher concentrationsare necessaryto achieveinactivation.Modeof actionof iodine
Similar to chlorine, the exactmodeof actionof iodineis not known.Iodine
penetrates into microorganisms and attacks specific groups of proteins,
nucleotidesand fattyacidsin a waycomparableto chlorine (McDonnell and
Russell, 1999). The effective concentration of iodine is approximately
100 mg lˇ^1 which is as effectiveas 300 mg lˇ^1 of chlorine(Krop,1990).
4.2.2 Quaternary ammoniumcompounds(QACs)
QACs can be dividedin two mainsubgroups(Mohr and Duggal,1997;Reuter,
1998):
∑ tri-alkylbenzyl-ammoniumcompounds(e.g.benzalkonium chloride);
∑ tetra-alkyl-ammonium compounds (e.g. didecyldimethyl-ammonium
chloride).
QACs combineantimicrobialpropertieswith surface-active propertiesand are
therefore useful for hardsurface cleaningand deodorisation(McDonnell and
Russell, 1999).Compared with chlorine theyare more expensive but havethe
advantage of having residual action. QACs remain active on surfaces for
approximately 1 day (e.g. fish industry) and therefore discourage furtherbacterial
growth (Tattersonand Windsor, 2001).Thisadherenceto the surfacealso has
disadvantages. Removing the disinfectantfromthe surfaceby flushingwith water
becomes difficult,resultingin possible residues in the product (Kraemer,1998).72 Handbookof hygiene controlin the foodindustry