Microbial Persistence on Inoculated Beef Plates Sprayed with Hypochlorite Solutions

Exterior surfaces of beef plates were inoculated with aerobic mesophilic, psychrotrophic, coliform, fecal coliform and Staphylococcus aureus bacteria before spraying with city water (7.03 kg/cm²) or with 100, 150 or 200 ppm hypochlorite solutions applied at 3.75, 5.25 or 7.03 kg/cm²) for 12 sec. Surface strips excised from the inoculated carcass regions were analyzed for bacterial persistence at 2 hand 2,4,8,16 and 20 days after spray treatment. A one log. or greater, reduction incoliforms, fecal coliforms and S. aureus counts occurred within 4 days for each spray treatment. Initial aerobic mesophilic and psychrotrophic counts were reduced by < 1 log within 2 h but increased to original inoculum levels within 8 days for each treatment. Mesophilic and psychrotrophic counts increased to > 3.5 logs higher than inoculated levels after 16 days at 4-6 C. Spray pressure (P < .01) was more effective in reducing mesophilic, psychrotrophic and S. aureus counts than was hypochlorite concentration (P < .05) while both variables were about equally effective against coliforms (P < .01) and fecal coliforms (P < .05). Surprisingly, reductions of psychrotrophic, coliform and S. aureus counts on the beef carcass surface sprayed with hypochlorite solutions were not significantly (P < .05) different from those observed on carcasses sprayed with city water. However, a significantly (P < .05) greater reduction in aerobic mesophile and fecal coliform counts at 2 days after treatment was obtained when using the intermediate spray pressure of 5.25 kg/cm² containing 200 ppm hypochlorite, rather than city water. No undesirable change in beef grade, muscle shear or color property was observed for carcasses treated with the hypochlorite solutions.