4.3.2 Applicationof the rightcleaning/disinfecting conditions
The combinationof concentration,mechanical action,timeand temperatureis
of major importance for efficientcleaning anddisinfection. The applied
concentrationshould not be higheror lowerthanthe advisedconcentration.
Too highconcentrationscan leadto insolubilityand increasedcorrosiveness.
Concerning protein fouling,it is known that too highconcentrations of alkali
(>0.5%) resultin polymerisation of the proteinand forma rubberylayer
(Bird,1994;Jeurninkand Brinkman,1994).Thesekindsof rubberylayers
obstructand prevent the penetrationof cleaningand disinfecting solutioninto
the fouling,resultingin a decreased foulingremoval rate (Jeurninket al.,
1996).Concerning starchfouling,the concentrationsof alkalineededvary
between9 and 20%(w/v)(Bird,1994),which is quitedifferent fromthosefor
dairyprocesses.Therefore,the applied concentrationdepends on the typeof
fouling.
An increasein temperatureresultsin increased efficiency.However,for
dairy processes at temperatures above 80 ÎC the opposite effect can be
achieved,as proteinscoagulate, resultingin an increaseof foulinginsteadof
a decrease. In addition, for all processes, cleaningat temperatures above
80 ÎC resultsin higherenergyconsumption use without extracleaningbenefit
and can lead to damageto the equipment(corrosion).An optimalworking
temperature therefore is around70 ÎC. In combinationwiththe 0.5%alkaline
solution(for dairyenvironments)this is sufficientto inactivateany vegetative
pathogenicmicroorganism (Jeurninket al., 1996).In the caseof membrane
systemsevenlowertemperatures(40±60ÎC) are advised,owingto the rather
vulnerablecompositionof the membranes and its modules(Shorrocket al.,
1998).
Contact timeis the thirdimportant parameter of disinfectionprocesses. The
longerthe contacttime,the greaterthe number of microorganismsinactivated.
In mostcasesthereis a directlinkbetween contact timeand concentration.
Thereare variousmodelspredicting the inactivationof a disinfectant but not all
of themare easyto use (e.g.too manyunknown parameters).In general, the
simpleChick-Watson(1908)log-linear model is used(Lambert and Johnston,
2000;Kamaseet al., 2003; Choet al., 2003):
log
N 1
N 0
àˇkCnt Ö 4 : 1 ÜwhereN 1 ànumber of surviving microorganisms, N 0 àinitial number of
microorganisms,kàdisinfectionrate constant,Càdisinfectantconcentration,
nàdilutioncoefficient andtàcontacttime.
The dilutioncoefficient(n) differs per typeof disinfectant.For example, for
QACsnà1, whichimplies that by halvingthe concentrationthe contacttime
(t) is doubled. For ethanolnà10 whichimpliesan efficiency reduction by a
factorof 2^10 (= 1024)whenhalvingthe concentration(Krop,1990).
The effect of mechanicalactionis obvious; the more mechanical energy is
put intothe removalof the fouling the moreefficiently the fouling willbe
Pathogen resistanceto sanitisers 79