3.2.3. Working suspensions and determination of threshold value
Working suspensions used in the pressure experiments were set
at initial levels of Listeria and yeast cell contents of 6.80 ± 0.09 and
6.33 ± 0.07 Log cfu/mL, respectively.
No significant differences (p > 0.05) between the mean values of
non-selective and selective media counts were observed in the
working suspensions. The threshold value, calculated as one SD
above the mean sublethal-injury percentage of the working suspension
data set (10), was 25.2%. Following the formula of Hansen
& Knøechel (2001), such a percentage corresponds to a difference
of 0.126 Log cfu/mL between counts on the two different media.