information, thus onlyproperties of the top nanometre/micrometrelayers will be
detected. Furthermore, the expense and accessibilityof thesemethodspreclude
theiruse in routine testing,although findings mayhelpsupport the rationalefor
experimental development. X-ray photoelectron microscopy (XPS) gives
information aboutthe distribution of elementsacrossa surface. Whena starch
soil was mixedwithmicroorganisms,a nitrogen peakcould be usedto monitor
the removal of microorganismsfromthe surface(Boydet al., 2001a). The surface
topographyagainhad no effecton cell removalin the presenceof soil. However,
XPSalso providedinformation on the natureof the bondsin whichelementsare
present: thus the presenceof markersassociatedwithstarch could be detected,
showingthat starch was retainedin largerquantities in the test stainlesssteel
substrata with the larger, deeper surfacefeatures.This methodwas usefulbecause
the starch soil lacked nitrogen, enabling discrimination between the two
components:othercell±soil combinationswouldnot be so readily differentiated.
34.5 Futuretrends
Bothrelatively simple routinemethods(epifluorescence microscopyand cell
culture) and morecomplex,expensiveand time-consuming surface-sensitive
techniques (XPSand AFM) confirmedthat the behaviourof soil and cellson
surfaces is not necessarily the samewhen monitoringsubstrata for hygienic
statusand cleanability.Severalvariablesshould be included in any rigorous
testingmethod,alongwiththe use of surfaces whichhavebeenexposedto some
element of wear:
- Intendeduse, environment,relevant soil and microorganisms.
- Effect of wearand ageingon substratumchemistry and topography.
- Modeof actionof any antimicrobial/detergent/selfcleaningeffect.
- Effect of repeated fouling and cleaning on surface properties and
cleanability. - Interactionsoccurringbetween substratum topographicfeatures, organic
soil and microorganisms. - Simple to perform,repeatable and valid.
Thedevelopment of novel food technologies, hygienic materials, finishes,
coatings, and cleaning and sanitizing applicationsshould requirethe concomi-
tant development of realistic, relevant and challenging test methods for
evaluation of the surfacecleanability and hygienicstatus.
The methods used to obtain results which support the claims of the
manufacturersshould be appropriateto the intended modeof actionof any novel
application.However, oncein use, in orderfor cleanability testingand hygiene
monitoring to be carriedout withrelative easeand reproducibility by the
relevant staff,organisationor validatingbody,thenthe routine methodsulti-
matelyusedneedto be relatively simple,rapid,cheapand valid.Thisis a
challenge for all concerned.
Testing surfacecleanability in foodprocessing 567