There was a significant interaction between dissolved CO2 and
microbial population type (p b 0.0484). This was expected because
different microbial populations have different sensitivities to dissolved
CO2 concentrations, with LAB having the greatest resistance, and
B. thermosphacta and Enterobacteriaceae having intermediate resistance
(Dixon & Kell, 1989). There was also a significant interaction between the
dissolved O2 concentration and microbial population type (p b 0.0066).
The dissolved O2 concentration effect had the most influence during the
first 5 days within the package because that is when the greatest decrease
in O2 occurred (Section 3.2). This decrease in O2 concentration resulted in
an anaerobic environment in the vacuum-package. The APC bacterial
population increased by log10 0.87 CFU/g, while the B. thermosphacta
and Enterobacteriaceae populations increased by log10 2.48 CFU/g and by
log10 2.96 CFU/g, respectively. In contrast, the LAB population decreased
by log10 1.83 CFU/g. This observed decrease in population could be attributable
to the higher oxygen content in the initial vacuum-package resulted
in a temporary population reduction, as LAB have a primarily anaerobic
metabolism (Hammes & Hertel, 2006). As the oxygen concentrations
decreased after day 5, the absence of dissolved O2 allowed the LAB to
grow rapidly