addition to this,many of the cellswithinthe biofilmare physically protected
fromthe effects of cleaningagentsby the structureof the biofilmand so are able
to carryon growingnormally aftercleaning(Holahet al.1994,Lewis2001).
Oneof the majorproblems is that chemical-based cleaningregimes havelittle
effect on the structure of the biofilm. A cleaning protocol that destroys
microorganismsand removesthe biofilmwould, therefore, be beneficial.
Theeffectiveness of ozonated water and traditional chemicalbeer line
cleanerwas investigatedagainstbiofilmin beerlines.The ozonatedwaterwas
produced by a WL2AdvancedOxidantGenerator(AOG,OzoneManufacturing/
IMI Cornelius).The investigation revealed that both systemswereeffective at
reducing biofilmfrominitial levelsby 99.98%(ozone) and 99.85%(chemical).
The ozonegavea statisticallysignificantly lowernumberthanthe chemical
cleanerfor tubing samplesin a model beer line system. Thesefindingswere
supported by the direct observation of the biofilm using epifluorescent
microscopy, which showed that the ozone removed large portions of the
biofilm fromthe glass slidewhereasthe chemical cleaner merelykilleda
proportion of the cells.
31.5.2 Monitoring ozonelevelsin air and water
Kimet al.(1998)grouped the analyticalmethodsfor the detectionand measure-
ment of ozoneintothreecategories. These are physical methods,physico-
chemical methodsand chemical methods. The physical methodsare basedon
measuringthe intensity of absorptionof lightin the UV, IR or visibleregionsof
the electromagnetic spectrum. Examples are the Ozone Photometer, which can
measureozone(gaseousor aqueous) and the API Model450 Ozone Monitor,
whichcan measuregaseous ozonein the regionof 1±1000ppm (Anon1999).
Physicochemical methodsrely on measuring the physicaleffects produced
when ozone reacts with suitable reagents. The effects measured include
chemiluminescenceor heat of reaction.Chemical methodsrely on measuring the
products formedwhen ozoneundergoesa chemical reactionwithan appropriate
reagent, or the reductionin molecular weightof a polymerwhenit reactswith
ozone.An example of a chemical detectionmethodis the Indigocolorimetric
method.Ozone adds acrossthe carbon±carbon doublebondof sulphonated
indigo dye and it decolourizes.The amount of ozonepresentis proportionalto
the amountof decoloration,whichcan be determined spectrophotometrically.
Dra»ger tubesconsistof a tubeand a pump,whichdrawsair into the tube.The
ozonereacts withthe indigoin the tubefilling.Thesedevicesmeasure 0.05±
0.7 ppmand 20±300ppm,whichexcludesthe rangecommonlyusedin food
processing(Anon1998b).
31.5.3 Dispersalof ozone
The dispersalof ozoneis mediatedby its reactionwithorganic compounds.
Ozone dispersal is morerapid in waterthanin air, initiated by chainreaction
involvingOH (Bott1991).Staehelin and Hoigne(1985)determined that the rate
512 Handbookof hygiene controlin the foodindustry