Influence of hot-processing and electrical stimulation on the bacteriology and retail case-life of vacuum packaged lamb

Abstract

Carcasses from 48 wether lambs 6 to 9 months of age were utilized to evaluate the effects of hot-processing and electrical stimulation on bacterial numbers and types of bacteria on lamb cuts, following vacuum packaged storage and during simulated retail display. Carcasses were subdivided into groups of 16. One subgroup was processed conventionally or chilled for 24 h at 1 °C. Another subgroup was electrically stimulated (20; 2 s pulses interspersed with 1 s resting intervals; 550V, AC, 50–60 cycles/s) at approximately 45 min post mortem and then chilled conventionally at 1 °C until 24 h post mortem. The final subgroup was treated identically to the subgroup receiving electrical stimulation, but was hotboned immediately following stimulation, vacuum packaged, and chilled at 1 °C until 24 h post mortem. At 24 h post mortem the racks from conventional and electrically stimulated carcasses were removed and vacuum packaged. All vacuum packaged racks were then randomly allocated to four post mortem storage intervals (0, 14, 28 and 42 days) within processing treatments, so that four racks from each processing treatment were evaluated at each storage interval. Following storage for the designated intervals, racks were fabricated into chops. The two centre chops from each rack were placed into styrofoam trays, overwrapped with oxygen permeable film and displayed under simulated retail conditions for 5 days. Racks were sampled for bacteriological analyses before and immediately after storage and chops were sampled before and after 5 days of simulated retail display. Four bacterial groups were enumerated (psychrotrophs, pseudomonads, lactics and Brochothrix thermosphacta). Processing treatments were not found to have any consistent effects upon bacterial populations except for the absence of B. thermosphacta on hot-boned and electrically stimulated racks. Neither storage time nor processing treatment produced a significant effect on retail case-life. Consequently, lamb carcasses can be processed using electrical stimulation and hot-boning alone or in combination to increase processing efficiency; and cuts can be stored in vacuum for up to 42 days without reducing the case-life of retail cuts below an acceptable level of 2 to 3 days.