differences (p > 0.05) due to the two muscle types or packaging
(aerobic/vacuum) were detectable. Therefore, the results were
combined and are shown in Table 2. Overall, the 3 treatments
caused significant reductions in the number of survivors in all 4
groups. It is worth noting that storage day had a significant
(p < 0.05) effect on bacterial groups B to D, where a general trend
toward decreasing numbers of survivors with storage time was
evident. A similar observation was made by Gamage et al. (1997)
with ground beef irradiated at 2.2e2.4 kGy during the first two
weeks of storage at 2 C.
After inoculation with 5 log CFU/g of Salmonella (group D), 5%
lactic acid combined with irradiation was the most effective
treatment in reducing the viability of the pathogen. Lactic acid plus
irradiation caused a 4.5 log CFU/g
reduction throughout storage.
Lactic acid was far less effective in reducing the numbers of
E. coli compared to Salmonella, and the similar log reductions after
lactic acid plus irradiation and irradiation alone showed that lactic
acid did not appear to sensitize E. coli strains to subsequent irradiation
challenge. The numbers of surviving E. coli and Salmonella
recovered on selective and non-selective media were not signifi-
cantly different, although slightly larger numbers of E. coli on LMG
agar were recovered from the lactic acid-treated samples.
In the second part of the study, inoculated samples were treated
with lactic acid, vacuum-packed and refrigerated at 4 C or frozen
at 20 C. The samples were then treated with 1, 3 or 7 kGy e-beam
irradiation. Results shown in Table 3 represent the number of surviving
injured and uninjured bacteria.
E. coli from groups A, B and C were not detected by plating
frozen samples irradiated at 3 or 7 kGy with or without lactic acid
pre-treatment. An average 2 log CFU/g reduction of E. coli was
found in the frozen meat samples irradiated at 1 kGy. When lactic