Assessment of the hygienic performances of two beef carcass cooling processes from product temperature history data or enumeration of bacteria on carcass surfaces

The carcass cooling processes at two beef slaughtering plants 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 carcases. 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. Carcasses resided in the chiller at plant A for between 15.8 and 28.0 h, but for between 20.0 and 24.0 h at plant B. The ranges of minimum temperature attained at all three types of site were generally lower at plant B than at plant A. However, 1/25 carcasses at both plants had high minimum temperatures indicative of ineffective cooling. An E. coli proliferation value was calculated for each temperature history from a surface site. The sets of proliferation values for aitch bone pocket sites on carcasses passing through either process complied with three points of a four point criteria for acceptable carcass cooling, but one value in each exceeded the stipulated maximum value. Proliferation values for randomly selected sites indicated that if temperature alone controlled bacterial growth during cooling, then numbers of E. coli on cooling carcasses would on average increase by about 1 log unit at plant A but by only about 0.3 log units at plant B. However, enumeration of bacteria showed that cooling reduced the mean numbers of total counts, coliforms and E. coli on carcasses at plant A by <0.5 log units, while at plant B, cooling reduced the mean numbers of total counts by about 0.5 log units, and mean numbers of coliforms and E. coli by 2 log units. The findings indicate that microbiological data are required to properly assess the hygienic effects of carcass cooling processes, but that temperature history data may be conveniently used for monitoring the maintenance of standard operating procedures in such processes. (C) 1997 Academic Press Limited.