to adhereto surfaces (Lunde¬net al., 2002).The contaminationwasfinally
eradicated afterthoroughdisassemblyof the machine and harsh alkali±acid±
alkalitreatments.
33.4 Psychrotrophiclacticacidbacteriumcontaminationin
meatprocessing environments
33.4.1 Lactic acidbacteriaand microbial ecologyof packagedmeat
products
Vacuumor modifiedatmosphere packagingis commonly usedfor increasing the
shelf-life and hygienic handling of meatproducts. Owing to the anaerobic
atmosphere created by these packagingtechniques, LABare the majorspoilage-
causingbacteriain theseproducts (Borchet al., 1996).SomeLABare also
resistantto the effectof smoke and nitriteand toleraterelatively highNaCl
concentrationswhichenablesthemto growalso in cookedmeatproducts, such
as cured hamand sausages(Korkeala and Bjo»rkroth, 1996 ).
Metabolic activity of LABproduces the typical spoilage changes making
products eventually unfit for humanconsumption.Sourflavourand off-odour,
formation of CO 2 resulting in bulging of packages, slime formation and
discolorationsare typical sensory changes involvedin LABmeat spoilage.
Spoilagechanges are usuallydelayeduntilthe stationarygrowth phaseof LAB
(Reuter,1970;Korkealaet al., 1989),and a productis expectedto retain good
sensorial quality for severaldays.In comparisonto the aerobic spoilage rate,
LABspoilageis much slowerand therefore prolongedproduct shelf-life is
obtained by anaerobic packagingof meat.
Thereare differencesbetweenthe abilityof variousLABspeciesand strains
to spoilmeat products(Borchet al., 1996;Korkealaand Bjo»rkroth, 1996).On
the basisof LABenumeration,it cannot be determinedwhether a sample
contains species/strainslaterassociatedwiththe spoilage of a product. In the
studyof Bjo»rkrothet al.(2005), dealing withLABspoilage in MAP marinated
broiler legs,a clearswitch fromthe initialcontaminants to the spoilage-causing
LAB was detected during the storage at 6 ÎC. The results showed that
enterococci(35.7% of the initialLABpopulation) weredominating in the
freshproduct whereas carnobacteria(59.7%)dominatedwithinthe spoilage
LAB.Onlyabout19%of the initialLABcontaminantswerecarnobacteria and
no enterococci weredetected in the spoiled products. In general, when the initial
LAB population was compared with the spoilage LAB, a shift from
homofermentative cocci towardscarnobacteria,Lactobacillussakei/curvatus
and heterofermentativerodswas seenin this marinatedproduct.
Since all LABdetected in the food processing environment cannotbe
considered as spoilage causing,contaminationanalysesmust be basedon the
tracingof the rightstrains. If no prior knowledge existsof the spoilage-
associated strains/species, molecular typing methods provide tools for
distinguishingspoilage-associatedLABstrains fromthe `background noise'.
Contaminationroutes and analysis in foodprocessing environments 547