Micro-organisms mesophilic

The minimum F value is based only on microbial spore destruction. It is believed that F0 = 12 min is a realistic minimum value, since most mesophilic spore-forming micro-organisms have D values <0.5 min at 121°C. Even if Dm = 1.0 min, the spore log reduction value according to Eq. (10) would be 12. ... 

Cooling water systems generally operate in the range 20 - 50°C so that the micro-organisms likely to be encountered in these systems are mesophiles, but biofilms are likely to be encountered at any temperature below 90°C. 

Figure 2.8. Arrhenius plot (log of the growth rate versus temperature ) for a typical mesophilic micro-organism.

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