Changesin foodproduction also influence the contaminationand the growth
of pathogenic and spoilagebacteria.The use of the coldchainand changes in
packagingtechnology have causedthe selection of certain pathogenicand
spoilagebacteria.Psychrotrophic, anaerobicor facultative anaerobicbacteria
suchas Listeriamonocytogenes, non-proteolyticClostridiumbotulinumand
pathogenic Yersinia enterocolitica and Yersinia pseudoturberculosis have
become the mostimportantpathogenic bacteria,and psychrotrophic lacticacid
bacteria havebecomethe most importantbacterial spoilagepopulation.
Theprocessing lines of REPFED products are very complex, including
differentmachinesand conveyor belts.Duringpreparation,the products are
exposed to bacterialcontamination. As foodcontaminationis a complicated
phenomenon,its causeis not easilytraced. Whenpathogenicor specificspoilage
bacteria are foundin the finalproduct, the contamination sourcesshould be
detectedwith a thorough contaminationanalysis.
Contamination research has beenmarkedly developedsince1985.The most
importantdevelopment has beenthe application of DNA-based methods.In
earlier times,the bacterialgenusor specieswas determined, whereas nowwe
can detectcertain strains or cloneswithina speciesat differentstages of
processing.We can follow the wholeproductionline and find at whichstage the
product becomescontaminatedwiththe strainsfoundin the finalproduct.We
can alsodetermine the contamination of certain clones of virulentstrains or
specific spoilagemicroorganisms.The contaminationresearch has developed
and is stilldeveloping enormously. In the present paper we focuson the
contamination analysis ofL. monocytogenes and psychrotrophic lacticacid
bacteria.
33.2 Different typesof contamination analyses
33.2.1 Conventionalmicrobial detection and enumerationanalysesand
their limitations
Beforethe genomic era and the use of molecular methods, bacterial con-
taminationin foodprocessingwas studiedusingculture-dependent microbial
techniques.Contamination loadwas estimatedby different enumeration tech-
niques and pathogen detection by conventional, usually enrichment-based
culturing methods. Today,contamination analysesemploy a mixtureof culture-
basedand molecularapproaches.Thisdevelopmenthas beenwelcomesincethe
limitations of enumeration analyses and the lack of specific information
involved in the barespeciesleveldetectionof a contaminanthas clearly been
elucidatedin associationwithcertainindustrial foodhygienic problems.
Increasinginformationon specificspoilage organismshas revealed that total
bacterialcountshavelimitationsin showing the relevant sitesand sources of
bacterialcontaminationin foodprocessing. Our knowledgehas improved our
understanding of the microbial ecologyof foods. Throughthis knowledge we
can nowadaysbetteridentifythe relevantspoilageorganismsassociated with
540 Handbookof hygiene controlin the foodindustry