Packaging of Beef Loin Steaks in 75% O₂ Plus 25% CO₂. II. Microbiological Properties

Numbers and types of bacteria were determined on steaks after refrigerated storage (1 ± 1 C) in 75% O₂ plus 25% CO₂ for 9 days in the dark plus display at 2 ± 2 C for 4 days under simulated retail conditions. Steaks were prepared from strip loins (IMPS #180) as received from the supplier (trial 1) and also from the same or similar loins that were vacuum-packaged at day 0 (trial 1) and then stored under refrigeration for 14 (trial 2) or 28 days (trial 3). Initially (day 0, trial 1), the microflora of steaks consisted primarily of Micrococcus and Moraxella-Acinetobacter sp. Following refrigerated storage in vacuum packages for either 14 or 28 days, Lactobacillus and Leuconostoc sp. became dominant. Refrigerated storage and display of steaks in 75%O₂ plus 25% CO₂ shifted the microbial population in favor of Leuconostoc sp. Initial log counts of steaks (day 0, trial 1) ranged from 0.88 to 2.02. Counts of steaks stored for 9 or 13 days in 75% O₂ plus 25% CO₂ nearly always exceeded 10⁶ per cm² when steaks were prepared from loins which had been stored in vacuum packages for either 14 or 28 days. The pH values of steaks prepared from loins which had been stored under refrigeration for 14 days were lower (0.27-0.56) than those of steaks prepared from comparable loins as they were received from the supplier (day 0, trial 1). Refrigerated storage of vacuum-packaged loins for an additional 14 days did not cause marked changes in pH of the steaks. No consistent differences in microbial flora were detected between green- and normal-pigmented areas of steaks prepared from vacuum-packaged loins which had been stored refrigerated for 14-28 days.