Microbial Quality of Ground Beef after Simulated Freezer Failure

Abstract

Six lots of ground meat, obtained at intervals from a local supermarket, were frozen, and later held with other frozen foods in the freezer compartment of a refrigerator-freezer where power failure was simulated by unplugging the unit. Mean values for the counts (log10) of the beef as purchased were as follows: aerobic and psychrotrophic plate counts 6.35 and 6.66, respectively; presumptive coliforms 4.48; coagulase-positive staphylococci 4.67; and presumptive Clostridium perfringens 1.43. Presumptive salmonellae were detected in three of the six lots. Counts of the same order of magnitude as above were obtained after 7 days in the freezers, complete defrost of the meat and 6 h thereafter. Between 6 and 24 h, aerobic and psychrotrophic plate counts and numbers of coliforms and coagulase-positive staphylococci increased approximately 10-fold. Forty-eight hours after complete defrost, further increases in counts occurred. The appearance and aroma of the meat were acceptable 24 h after defrost; after 48 h, it would have been discarded because of browning, slime and off-odors.