17.5 Microbial growthin pipingsystems
Mostof the product will remain withinthe systemfor a shortertimethanthat
needed for the microorganismsto multiply.Onlya verysmall fractionof the
product flowscloseto the pipewallsand residessufficientlylongto allow
growth. Wouldthe growthin this verysmallvolumebe ableto increasethe
number of microorganismsin the mainflow?To verifythis, a simplesimulation
was madefor a viscousNewtonian flowthrougha straight pipewithan average
residence timein the pipeof 5, 8, 16 minutes,muchless thanthe doubling time
of 20 minutes.The initialconcentrationis 100 microorganisms/ml. Figure17.1
shows the averageconcentrationof microorganismsat the pipeexit.Fromthe
simulationwe learnthat althoughthe volumeavailable for growthis small,the
exponential nature will lead to a significant increase in the number of
microorganismsin the mainflow.This also impliesthat hygienicequipmentwill
havea limitedrun lengthwhen microorganismsare ableto growwithinthe
system.
Moreand moreantimicrobial materialsare being introducedto the market
and it wouldbe interestingto knowif the antimicrobialaction also penetrates
sufficientlyinto the productto stop the growth. Exampleswherethis problem
Fig. 17.1Averageconcentrationof microorganismsat the pipeexit.276 Handbookof hygiene controlin the foodindustry