The dissolved O2 concentrations decreased significantly over time
(p b 0.0001) in the purge of the vacuum-packaged pork chops (Fig. 4).
On day 0, the dissolved O2 concentrations was 8.31 mg/L before
decreasing to 0.326 mg/L on day 5. This decrease in dissolved O2
concentrations occurred because there was an approximate log10
3 CFU/g increase in bacterial populations between day 0 and day 5. As
the bacterial populations increased, their cellular metabolism would
have resulted in the dissolved O2 being converted to CO2 (Dainty &
Mackey, 1992). Between day 15 and day 45, the dissolved O2 concentrations
remained around 0.11 mg/L but on day 60, they increased slightly
to 0.15 mg/L. The dissolved O2 concentrations increased slightly at the
end of the storage period because there was a loss in vacuum and gas
permeation through the packaging film. Gas permeation through the
packaging film occurred because the had an O2 transmission rate of
3–6 cm3
/m2
, 24 h, 1 atm, at 4.4 °C and 0% relative humidity. Since the
dissolved O2 concentrations in the present study remain below
0.20 mg/L, or 2%, throughout the storage period after day 5, it is consistent
with the literature that O2 concentrations in vacuum-packages
remains around 1% after sealing (Dainty & Mackey, 1992).
The results of these experiments demonstrated that the spoilage
bacteria in vacuum-packaged pork chops increase the dissolved CO2
and decrease the dissolved O2 concentrations. The dissolved CO2 concentrations
increased because of increasing LAB concentrations that produce
CO2 as a metabolism by-product (Hammes & Hertel, 2006). The increasing
spoilage bacteria concentrations also decrease the dissolved O2
concentrations because of the increased rates of cellular respiration occurring
(Dainty & Mackey, 1992). These results also showed that LAB dominate
the spoilage flora of vacuum-packaged pork chops because they had
the highest microbial populations throughout the storage period, either
core or purge. After LAB, the Enterobacteriaceae had the second highest
populations and also contributed to spoilage, but did not dominate the
spoilage flora. B. thermosphacta also contributes to spoilage, but they
also do not dominate because they had the lowest populations out of all
the bacterial types measured.