2.5. Enumeration of microorganisms
In order to determine the correlation between number of microorganisms
and the CO2 signal recorded by the R.A.B.I.T. instrument,
total colony counts were determined at various time points
for each microorganism and food matrix. At each time point,
replicate tubes containing the sample under test were recovered
from the instrument and a dilution series was prepared for each
sample point from 1 g of the 3 g inoculated sample using BPW as a
diluent. Twenty microliters of each dilution were spotted in triplicate
on appropriate agar plates to enumerate the bacteria. Colonies
were counted manually after incubation (24 h at 30 C or
37 C for bacteria or 48 h at 25 C for yeast).