3.4.2 Biofilm removal
Theeliminationof biofilmsis a verydifficult and demanding task,because
manyfactors affectthe detachment, suchas temperature,time, mechanical
forcesand chemical forces.Sanitation, i.e. cleaningand disinfection, is carried
out in foodprocessing plants in order to produce safe products with an
acceptable shelf-lifeand quality.The key to the effectivecleaningof a food
plantis the understanding of the typeand natureof the soil and of the microbial
growth on the surfaces to be removed. The intelligent integration of
decontaminationprogrammesin the manufacturing are essentialto achieve
bothsuccessfulcleaningand businessprofit(Lelieveldet al., 2003).Lelieveld as
earlyas 1985 wrotethat thereis a trendtowards longerproductionrunswith
shortintervalsfor sanitation,because the sanitationshould be performed as cost-
effectively and safely as possible.
The mechanical and chemical power,temperatureand contact timein the
cleaning regime shouldbe carefullychosen to achievean adequate cleaning
effect(Wirtanen, 1995).An efficientcleaning procedureconsists of a sequence
of rinsesand detergent and disinfectantapplications in various combinationsof
temperature and concentration,finally letting the equipmentand processlines
dry in well-ventilatedareas.Thebasictask of detergentsis to reducethe
interfacial tensions of soilsso that the soil attached to surfaces, for example
biofilm, becomes miscible in water.The effect of the surfactantsis increasedby
the mechanicaleffectof turbulent flow or waterpressure,or by abrasives,for
example salt crystals. Prolongedexposure of the surfaces to the detergent makes
removalmoreefficient. Detergentsto be usedin the cleaningof opensystems
are formulatedto be effectiveat temperaturesin the range35±50ÎC. In closed
systems the detergentsare formulated to be usedat temperaturesin the rangeof
55±80ÎC (Troller, 1993;Wirtanenet al., 2002).
Elimination of biofilms in opensystemsis performedas follows:grosssoil
shouldbe removedby dry methods, e.g. brushing, scraping or vacuuming, and,
if the processis wet,the visiblesoil can be rinsedoff withlow-pressurewater.
The effective elimination of biofilms from open systems is achieved by
dismantlingthe equipment in the processline and cleaningis thencarriedout
usingeitherfoamor gel. Foams are most effectivein situations wherecontact
withthe soil for an extendedcontacttimeis necessary.The surfactants, which
suspend the adheredparticles and microbes fromthe surfaces in the water,are
addedto increase the cleaning effect,whichis also increasedby using waterof
sufficientvolume at the correct temperatureand pressure. Thedismantled
equipment and utensilsshouldthereafterbe storedon racksand tables, not on
the floor.Thecleaning is mostly carriedout in combinationwitha final
disinfection, because viable microbes on the surfaces are likely to harm
production (Troller, 1993;Wirtanenet al., 2000a).
In the cleaningregime for closedprocesses,pre-rinsing withcoldwateris
carriedout to removeloosesoil.Cleaning-in-place(CIP) treatment is normally
performed usinghot cleaningsolutions,but coldsolutionscan also be usedin
the processing of fat-free products. Thewarm alkaline cleaning solution,
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