24.2.2 Fungi and actinobacteriain end-products
Fungimaypresent a potentialfoodspoilage risk because of theirabilityto
degrade,ferment or convertsubstratesas well as to produceodorous metabolites
(off-flavours)and mycotoxins.The growthof fungion paperand paperboardis
quitecommon,especiallyunderconditions of highmoistureand low illumina-
tion (Piluso, 1987).The presenceof fungiis primarily due to postcontamination
via air and water during and after product manufacture. Aspergillus,
Cladosporium,Fusarium,MucorandPenicilliumspecieshavebeenisolated
fromfibreboardcartons(Tindaleet al., 1989).Suihkoand Hoekstra (1999)
isolatedyeastsand mouldsfromrecycledfibrepulpsand paperboards. They
observed that the drying stages of the paper and boardmaking processes
drastically eliminated the fungipresent in the recycledfibrepulps and process
water,but not during the heat dispersal.Mouldswerepresent in all paperboard
samples; however, the numbers werecloseto the detectionlimit(10 cfu gˇ^1 ).
The dominant speciesoccurring in all the recycled fibreboards wasGilmaniella
humicola;Paecilomyces variotiiwas as wellalso found(Suihko and Hoekstra,
1999). The mill environment (air) or the boardmaking chemicals were
considered to be the likely contaminationsources. The low level of contamina-
tion by microorganismsof food-gradepapersurfaces indicates that the risk for
foodcontaminationis low.However, whenpasteurisedand sterile foodsare
packed the demandsfor the packagingmaterials are high.Fungalascosporescan
contaminateproducts of low pH duringlong-term storageif migration through
pinholes occurs. The spoilageof fruitjuicebyPenicilliumspeciesoriginating
fromcartonmaterial havebeenreported(Narciso and Parish, 1997).
Actinobacteriaare a large groupof morphologically and physiologically
diverse, Gram-positivebacteria, havingin commonDNAwithan unusually high
GC content (Ensign, 1992). The morphological diversity ranges from the
micrococcito the branchedfilament-forming species. Actinobacteriainclude,
e.g.,the generaActinomyces,Mycobacterium, Frankia, Nocardia,Micrococcus
andStreptomyces.Actinobacteria are the mostprevalent producers of organic
odours. The mycelialactinobacteriaare ableto causeproblemsin paperand
boardproduction and odourproblems in the finalproduct by producing volatile
metabolites,mainlygeosmins. Furthermore, many streptomyceteshavebeen
reported to produce antibiotics and some, likeS. anulatus, may produce
genotoxins. Thermophilicactinobacteriahavebeenisolated up to 10^2 cfu gˇ^1 dry
weightfromboardsamples on whichrecycled fibre pulps had beenused(Suihko
and Skytta», 1997).
24.2.3 Migrationof microorganismsintofoodsfromthe packaging
material
Mostpackagingmaterials have proven to be completelyimpervious to micro-
organisms.Moreover,the microbialload of freshfoodproducts is incomparably
largerelativeto the amounts of microorganismsthat couldpermeate througha
package, so this phenomenon can usually be neglected(Ho»utmann, 1999).
Managingcontaminationrisksfromfoodpackagingmaterials 385