To enable an assessment of the uncertainty of cell enumeration
by the classical plating method (International Standard
Organization, 2006) and to obtain standardized samples, 10 working
suspensions were prepared, and their exact microbial contents
were quantified. In either fresh or treated cultures, a fraction of the
microbial population may be in a sub-lethally injured status, and
mild conditions are required for their cultivation (Besse, 2002).
However, because selective media are normally used to enumerate
microbial species in foods, an assessment of the sub-lethal injury is
needed and is performed by comparing the selective and nonselective
media counts, at least for the pathogenic species of
concern (L. monocytogenes in this study). In addition, the performance
of selective media in supporting the growth of intact cells
compared to the non-selective one must be determined.
The yeast content of the corresponding working suspensions
was estimated by plating decimal dilutions on YPD non-selective
agar medium and incubating the plates for 72 h at 30 C.
The L. monocytogenes inoculum level was determined by plating
decimal dilutions of working suspensions on both selective ALOA