MICROBIOLOGY OF BEEF SHELL FROZEN WITH LIQUID NITROGEN

SUMMARY— The effect of freezing primal cuts of beef with liquid nitrogen on the subsequent microbiological quality of their retail cuts was studied. Cryovac-packaged loins were shell frozen by spraying with liquid nitrogen and held for 2 or 3 days at room temperature (25–27°C) in insulated styrofoam boxes. Frozen packaged loins were also aged at 2°C for 21 days and at 22°C for 3 days before being cut into steaks. Steaks from each treated loin and steaks from fresh loins (controls) were packaged and stored in a display case at about 5°C. Examination was made of the loins and packaged steaks during storage to determine total anaerobes, fluorescent Pseudomonas , coliforms, enterococci, Clostridium perfringens , and incidence of Salmonellae and coagulase-positive staphylococci. Initial contamination on steaks increased with loins aged for a long time at low temperatures. Aging of loins at 22°C for 3 days promoted multiplication of C. perfringens and resulted in the steaks having the highest occurrence of coagulase positive Staphylococcus . Recovery of Salmonella from the steaks was more closely related to the source and level of contamination of the fresh meat than to time and temperature of holding of the wholesale cuts. These findings have application to shell freezing of beef with liquid nitrogen for air transport and to possible commercial aging practices.