microorganisms that can cause colour defects in products and
microorganismsharmful to the hygiene of the end-product, e.g.Bacillus
cereus,Staphylococcus aureus, coliforms and moulds.
∑ Microorganismsthat can causesmellor tastedefects, suchas the volatile,
foul-smelling compounds produced during microbial metabolism, e.g.
Clostridiumspp.,Desulfovibriospp. and actinobacteria.
Importantpotentialcontaminants in the paperand packagingindustry and their
characteristicsare summarisedin Table 24.1.
Thereare two waysin whichmicroorganismsmaycontaminatethe end-
product: duringthe manufacturingprocess when microorganisms are found
withinthe products(mainlydue to the microbial qualityof the fibre,water,
aerosols and pulpadditives),or at a laterstate duringrecolonisation,when
microorganisms are found on the surface of the product (airborne micro-
organisms,aerosols, handling by personneland storage conditions). Micro-
organismscan enterthe production facilities via raw materials, e.g freshwater,
raw materials and additivessuchas fillers, pigments,starchesand coatings.
Furthermore harmful microorganisms can enter via packaging materials,
transport equipment, open windows, doors and openings, air conditioning,
insects and pestsand personneland settleinto the production facilitities.Con-
tamination risk depends on the source of contaminant,number of micro-
organisms, quality of microorganisms, conditions in production premises
(temperature,moisture, pH),availabilityof nutrientsand efficiencyof control
methods (Fig. 24.1). The characteristics of some important groups of
contaminantsare describedin the following sections.
24.2.1 Spore-formingbacteriain end-products
Heatand steamin the dryernormally kill bacterial vegetative cells.However,
certainspecies of bacteria formendosporesthat are highlyresistantto heat,
desiccation, disinfectants, chemicalbiocides, ultraviolet light and ionising
radiation. The surviving free sporescan remain dormantuntilexternal conditions
are favourablefor germinationand development intovegetativecells. Heat-
stableenzymes and toxinscan alsobe problematic if migration into delicate
foodstuffsoccurs (Pirttija»rvi, 2000).Thisis most likely withproducts having a
highgrammage,where the thicknessof the product protectsthe microorganisms
fromheatduringthe dryingstage.Microorganisms also withstandheatwellin
end-productscontainingmineralsby adheringto the mineral crystals.Fromthe
pointof viewof end-products safety, the most importantmicroorganismsinclude
spore-forming bacteria (Bacillus spp., Clostridium spp.), bacteria that are
injuriousto health,certainmoulds,actinobacteria and anaerobic bacteria.
Aerobic endospore-formingbacteriaare widelydistributedin nature. The
sporesare resistant to heat,desiccation,disinfectants,ionising radiation and
ultravioletlight(Russell,1990).Spore-formingbacteriaare commonin mill
watercirculations and havealso beenisolatedfromboardsamples.Studieshave
shownthatthe main contaminantsin food-packaging paperand boardare
Managingcontaminationrisksfromfoodpackagingmaterials 381