B. thermosphacta contributed to spoilage but had the lowest microbial
population compared to the other types of bacteria enumerated in the
core and purge samples. B. thermosphacta populations on core samples
for day 0 were log10 2.9 CFU/cm2 and increased to log10 3.47 CFU/cm2
by day 5, and remained at approximately log10 4.5 CFU/cm2 for the
remainder of the storage period (Fig. 2). Similar populations
for B. thermosphacta were found in the purge samples, with log10
2 CFU/mL on day 0 and increasing to log10 3.7 CFU/mL by day 30
(Fig. 3). On day 45, the B. thermosphacta populations reached log10
4.1 CFU/mL before decreasing to log10 2.91 CFU/mL by day 60. The
B. thermosphacta populations in this study were lower than those
found by Blixt and Borch (2002), who reported B. thermosphacta populations
of approximately log10 3–4 CFU/g on pork loins after 56 days at
4 °C. However, this may be attributable to higher concentrations of lactic
acid in the purge of this study, as B. thermosphacta is inhibited by lactic
acid at 5 °C (Grau, 1980). B. thermosphacta also has a faster anaerobic
growth rate when the pH is greater than 5.8 (Knox et al., 2008). The
surface pH in the study presented here was 5.7, which may have resulted
in a slower growth rate for B. thermosphacta. The initial populations of
B. thermosphacta, in the present study, log10 2.9 CFU/cm2
, were similar to
those reported by Nowak et al. (2012), who reported B. thermosphacta
populations on pork loins between log10 3–6 CFU/g.