Microbiologic evaluation of carcasses before and after washing in a beef slaughter plant

The effect of washing on the bacterial contamination of beef carcasses in a modern abattoir was evaluated. Twenty-six carcasses were evaluated at the end of the slaughter process before and after washing, and 13 other carcasses were evaluated only after being washed. An excision sample (5 x 5 x 0.5 cm) was collected from 10 sites on each carcass immediately before washing and at an adjacent site immediately after washing. Aerobic bacterial colonies were enumerated, using hydrophobic grid membrane filter technology. After washing, the log10 of the most probable number of growth units/cm2 decreased (P < 0.01) at the lateral rump site, increased (P < 0.01) at the thorax and neck sites, but was unchanged at the other 7 sites, compared with before washing. The sample size required to estimate, within 0.5 log10 units, the mean log10 most probable number of growth units/cm2 at a site for use in future group-carcass evaluations was determined and compared with a previously used sample size definition. It was concluded that the washing process described did not result in a major change in the bacterial contamination of carcasses.