Effects of Spray-Cooling Processes on the Microbiological Conditions of Decontaminated Beef Carcasses

Abstract

Spray processes for cooling decontaminated carcasses were examined at four beef packing plants. Temperature histories were collected from deep leg sites on 25 carcasses and from randomly selected sites on the surfaces of a further 25 carcasses selected at random from carcasses undergoing cooling at each plant. Carcass cooling rates were similar at all four plants. Proliferation values calculated from surface temperature histories indicated similar increases of ≤2 log units in the numbers of pseudomonads on carcasses at all plants and increases of <0.5 and >0.5 log units in the numbers of Escherichia coli on carcasses at plants A and B and plants C and D, respectively. The numbers of aerobes recovered from carcasses after cooling were about 1 log unit larger than the numbers recovered from carcasses before cooling at plants A, B, and C but >1.5 log units larger at plant D. These increases in numbers of aerobes were in agreement with the estimated proliferations of pseudomonads. The larger increase in the number of aerobes on carcasses at plant D may be attributable to carcasses not being pasteurized at that plant, while carcasses were pasteurized at all of the other plants. The numbers of E. coli recovered from carcasses after cooling at plants B, C, and D were also in agreement with the increases calculated from surface temperature histories. However, numbers of E. coli declined by about 1 log unit during carcass cooling at plant A. This decline may have been due to death occurring during chilling for some E. coli cells that were injured rather than killed by pasteurization with sprayed hot water at plant A, whereas pasteurization with steam at plants B and C seemingly left few injured E. coli cells. The growth of bacteria on decontaminated carcasses during spray cooling at the four plants was apparently constrained by temperature alone.