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Chapter 4
effective at eliminating all viable cells from the surface (7 log 10 reduction)
[219]. However cells were recovered from the biofilm (5 log 10 reduction) if
the cleaning temperature was reduced to 60°C or if the concentration was
reduced to 0.25M. This may have serious implications for the food
processing industry as the research presented in this chapter demonstrates
that cells can continues to form a dense biofilm over an extended period of
time and that this biofilm is more tolerant of disinfectant agents.
4.4.2. The log 10 reduction achieved by sodium hypochlorite
The research presented in this chapter indicates that sodium hypochlorite
inhibited cell growth using a suspension test method. However, viable cells
were recovered from a 48 hour and 168 biofilm after contact times of 10,
45 and 90 minutes. In most instances there was less than a 1 log 10
reduction after extensive contact (90 minutes) with the biofilm.
Møretrø et al. also found that sodium hypochlorite did not eliminate all
cells from a S. enterica biofilm (incorporating S. Agona and S.
Typhimurium) formed on glass slides after 48 hours [134]. Møretrø and
colleagues reported 0.5-1 log 10 reduction in the number of viable cells after
contact with sodium hypochlorite for 5 minutes. This broadly correlates
with the findings presented in this chapter, which also found that sodium
hypochlorite was not effective at reducing the number of cells recovered
from the surface. However the log 10 reduction of cells recovered from both
the 48 hour and 168 hour biofilm achieved in this research was lower in
most instances (~0.2-0.4 log 10 for the 48 hour biofilm) than what was
reported by Møretrø et al. [134]. Buckingham-Meyer et al. also found the
use of the CBR to produce a biofilm may resulting in a lower reduction after
treatment with disinfectants in comparison to other biofilm development
models which was previously discussed in section 4.5 has also been
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