Assessment of the hygienic performances of an air-cooling process for lamb carcasses and a spray-cooling process for pig carcasses

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The air-cooling process for carcasses at a lamb slaughtering plant and the blast-plus-spray-cooling process for carcasses at a pig slaughtering plant were examined. Temperature histories were collected from the deep leg, the aitch bone pocket surface and randomly selected surface sites of carcasses passing through each process. For each process, sets of 25 temperature histories were collected for each type of site, with a single history being collected from each of 75 randomly selected carcasses. A swab sample was obtained from a randomly selected site on each of 25 randomly selected carcasses entering and 25 leaving each process. Total aerobic counts, coliforms and Escherichia coli were enumerated in each sample. Lamb carcasses resided in the chiller for between 17.5 and 66.8 h, and pig carcasses for between 14.8 and 24.5 h. All the lamb carcasses attained deep leg and aitch bone pocket surface temperatures <7°C as did most pig carcasses. However, those temperatures remained >13°C in 8% of pig carcasses. Such inadequate cooling of pig carcasses was not apparent in temperature histories from randomly selected surface sites as such sites on both pig and lamb carcasses all attained temperatures <7°C. Proliferation values for E. coli and psychrotrophic pseudomonads calculated for the temperature history from each randomly selected surface site indicated that growth of E. coli on either lamb or pig carcasses would be undetectable, but that increases in the log numbers of total aerobic counts of >1 and <1 during the cooling processes could be expected for lamb and pig carcasses respectively. Enumerations of bacteria showed that bacteria on pig carcasses behaved much as would be expected from the temperature histories from randomly selected sites. However, on lamb carcasses the log numbers of bacteria were reduced by about 0.5, 1.5 and 2 for total aerobic counts, coliforms, and E. coli, respectively. The findings indicate that microbiological data are required to properly assess the microbiological effects of carcass cooling processes because, in some, factors other than temperature determine the behavior of the microflora.