Effect of incubation temperature on aerobic plate counts of beef and sheep carcasses

Australian regulations for microbiological testing of carcasses specify a number of incubation temperatures and media for meat processed at both domestic and export establishments. Accordingly, the effect of incubation temperature and media on aerobic plate counts of samples from beef and sheep carcasses was investigated. For both species, aerobic plate counts on Petrifilm incubated at 35 degrees C were significantly lower than those counts on Petrifilm and pour plates incubated at 25 and 30 degrees C, reflecting the inability of many psychrotrophs to grow at 35 degrees C. When samples were taken from carcasses that had been stored in abattoir chillers for periods between 16 h and 5 days, difference between counts at 35 degrees C versus those incubated at 25 and 30 degrees C became greater as the period of refrigerated storage increased. For export beef carcasses, the effect of this difference is minimal, since the vast majority of counts incubated at 35 degrees C are done on carcasses that have been chilled for less than 24 h and will not have a large proportion of psychrotrophs.