Question in review session 1

Question

21014-15 Final Exam Question B4

Answers

a. Number of D's in standard process 25 min 105C

bacteria 

D value=0.25 min
No. of D's = 25 min/0.25 min=100

spores

No. of D's 25/2.5=10

b. 
cell densities in contaminated lot:

Bacteria

10<5>/ml for 100 D reduction = 10<5>/10<100>=10<-95>/ml 

spores

10<4>/ml for 10 D reduction=10<-6>/ml

c. Use the curve to get Z values

bacteria

10C

spores

15C

d. 120C How long? Need to reduce the spores to 10<-8>/ml 

that is, from 10<4> to 10<-8>, or 12 D reduction

From Z value: D at 120C for spores is now 0.25min 

so 12D reduction requires 0.25min*12=3min

Calculate bacteria D value at 120C

0.25min/1.5=

Then calculate the time required for spores first. Use that time, calculate the reduction of bacteria. Then calculate the corresponding cell densities as you do with question a.