Mesophilic and Psychrotrophic Bacterial Populations on Hot-Boned and Conventionally Processed Beef'

Abstract

Mesophilic and psychrotrophic bacterial counts of hot-boned and conventionally treated cuts from 15 steers were low [Log 0-2 colony forming units (CFU)/cm 2 ] at 0 time; and after 14 days of vacuum-packaged storage (2.2 C), hot-boned cuts had higher counts than conventionally-treated cuts. In the first experiment involving 10 steers, the mesophilic and psychro-trophic counts for hot-boned cuts were Log 5.26 CFU/cm 2 and Log 5.15 CFU/cm 2 , respectively, and for conventionally treated cuts, log 4.64 CFU/cm 2 and Log 4.43 CFU/cm 2 , respectively. In the second experiment involving 5 steers, the mesophilic and psychrotrophic counts were Log 6.62 CFU/cm 2 and Log 6.61 CFU/cm 2 , respectively, for hot-boned cuts; and Log 5.93 CFU/cm 2 and Log 4.91 CFU/cm 2 , respectively, for conventionally treated cuts. Some hot-boned cuts had low levels (Log 0-3 CFU/cm 2) of coliforms, fecal coliforms, Clostridium perfrin-gens, coagulase-positive Staphylococcus aureus and fecal streptococci. No Salmonella were recovered from any cuts. Temperature-decline data indicated that hot-boned cuts had longer (~everal hours) periods of rapid bacterial growth (above 21 C) than conventionally-treated cuts. The longer rapid growth period for hot-boned cuts may have contributed to higher microbial loads and subsequently to more growth of bacteria in cold storage. Slower chilling of hot-boned samples stemmed from vacuum-packaging and boxing soon after cutting. Temperature control of hot-boned meat during the first several hours of chilling is critical, particularly if hot cuts are vacuum-packaged and boxed before chilling. Some temperature decline guidelines, based on bacterial counts, are presented for hot-boned, vacuum-packaged boxed cuts. Most hot-boned cuts processed and stored under our experimental conditions were bacteriologically acceptable. The potential advantages of hot-boning beef include facilitating centralized processing, reduced cooler space and reduced energy (refrigeration) input, with no reduction in cut yield (4). Those potential economic advantages have prompted an increased interest in hot-boning to produce subprimal beef cuts that can be vacuum-packaged and stored in boxes soon after cutting. To help insure that the process is safe, the microbiology of hot-boning (the number and kinds of microorganisms involved during processing and storage) must be understood and controlled, particularly for vacuum-packaged, hot-boned cuts. 'Contribution No. 79-380·J, Department of Animal Sciences and Industry. Kansas Agricultural Experiment Station, Manhattan 66506. Microbiological work on hot-boned beef and lamb (1,6,9,10,11) has shown counts of Log 3-6 CFU/cm 2 , g, or ml after 1 to 14 days of storage at 1 to 15 C, and that the cuts were generally bacteriologically acceptable. The purpose of this study was to ascertain mesophilic and psychrotrophic bacterial populations of hot-boned vacuum-packaged beef using conventionally chilled meat as a comparison. Occurrence of indicator organisms and potential pathogens in some meat samples was also monitored. MATERIALS AND METHODS Meat processing Fifteen steers were used in this study. Ten were slaughtered on two successive days (five per day) at hourly intervals in experiment one (September, 1978) and five were slaughtered at hourly intervals in experiment two (March, 1979). Half of each carcass was hot-boned within 2 h postmortem, and the other half of the same carcass was conventionally chilled and cut in the same manner at 48 h postmortem. Samples (32.26 cm 2) were removed aseptically from the plate region of the hanging carcass (12) at 2 h postmortem and after chilling 48 h at 2.2 C for "0" time samples representing hot-boned and conventionally-processed products, respectively. Thin samples (ca. 2.5 x 15 x 22 em) from the plate region (cut from the carcass exterior to the underlying connective tissue septa) were excised aseptically immediately adjacent to where "0" time samples had been removed. Then the thin samples were vacuum-packaged in very low gas and H 2 0 transmission bags (Cryovac SR823), boxed (24 x 56 x 32 em box) and stored at 2.2 C for 14 days. Subsamples (32.26 cm 2) were removed aseptically later for the 14-day analyses from the hot-boned and conventionally processed sides. In the first experiment, two samples (32.26 cm 2) adjacent to each other were removed per sampling time, and one sample was removed for each period in the second experiment. After 14 days of storage, all vacuum packages maintained a vacuum within the range of 23.0 to 26.8 inches of Hg. Inches of Hg were determined by the vacuum required to initiate separation of the packaging material from the meat sample. Temperature measurements In the first experiment, temperature of the hot·boned and conventionally processed meat was monitored at 2, 4, 6, 8 and 24 h postmortem under an ambient temperature of 2.2 C. Temperature measurements of semimembranosus and longissimus muscles were used as indicators of the relative chill rates between treatments. Metal dial thermometers were inserted S em into the muscles at constant muscle locations whether muscles were intact on the carcass or excised. In the second experiment, metal dial thermometers were inserted S em into the muscles of the carcass to measure temperature decline of conventionally chilled meat. To simulate commercial conditions, hot-boned vacuum-packaged plate samples were placed in the center of the box, sandwiched between hot meat masses from other parts of the carcass. Temperature was recorded at the center (adjacent to the surface of the plate samples) and S em inward from the exterior of the