Modified atmosphere packaging using CO, was demonstrated to be effective in retarding the growth of microorganisms during storage of fresh fish from the Gulf of Mexico. At 4"C, there was at least a log difference in bacterial counts at 2, 4, and 6 days between fish stored in CO, as compared to control fish stored without CO,. While the CO, atmosphere was shown to inhibit the growth of common spoilage types of bacteria such as gram-negative rods (Pseudomonas), stimulation of gram-positive bacteria such as Lactobacillus was also demonstrated. Fish stored at 4°C for 2-8 days in a modified atmosphere containing CO, had lower TVN values than fish stored at the same temperature without CO,. The results indicate that an extension of the shelf-life of fresh fish can be obtained by packaging and storing the fish in a CO, atmosphere.

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A study to compare procedures and interventions for removing physical and bacterial contamination from beef carcasses was conducted in six carcass conversion operations that were representative of modern, high-volume plants and located in five different states. Treatment procedures included trimming, washing, and the current industry practice of trimming followed by washing. In addition, hot (74 to 87.8°C at the pipe) water washing and rinsing with ozone (0.3 to 2.3 ppm) or hydrogen peroxide (5%) were applied as intervention treatments. Beef carcasses were deliberately contaminated with bovine fecal material at >4.0 log colony-forming units (CFU)/cm2 in order to be better able to observe the decontaminating effects of the treatments. Carcasses were visually scored by 2 to 3 trained personnel for the level of gross contamination before and after treatment. Samples (10 by 15 cm, 0.3 to 0.5 cm thick) for microbiological testing were excised as controls or after application of each procedure or intervention and analyzed for aerobic mesophilic plate counts, Escherichia coli Biotype I counts, and presence or absence of Listeria spp., Salmonella spp., and Escherichia coli O157:H7. Average reductions in aerobic plate counts were 1.85 and 2.00 log CFU/cm2 for the treatments of trimming-washing and hot-water washing, respectively. Hydrogen peroxide and ozone reduced aerobic plate counts by 1.14 and 1.30 log CFU/cm2, respectively. In general, trimming and washing of beef carcasses consistently resulted in low bacterial populations and scores for visible contamination. However, the data also indicated that hot- (74 to 87.8°C at the pipe) water washing was an effective intervention that reduced bacterial and fecal contamination in a consistent manner.

Swordfish (Xiphias gladius) steaks were held in retail packages containing 100% CO2 and in mixtures of 40% and 70% CO2 in combination with either oxygen or nitrogen. Controls were stored in air. Samples were removed for chemical and microbiological analyses after 2–22 d of storage at 3.5°C. The inhibitory effect of CO2 on psychrotrophic, aerobic gram-negative spoilage bacteria was proportional to the CO2 tension in the packages. Maximum inhibition of growth was achieved with 100% CO2. Except for steaks stored in 40% CO2:60% O2 heterofermentative Lactobacillus spp. became a dominant part of the microflora of steaks stored in CO2-enriched atmospheres. Pseudomonas spp. continued to be a major part of the microflora of steaks stored in 40% CO2:60% O2. During the first 2 d of storage, there was a decrease in the surface pH of the swordfish steaks proportional to the CO2 tension in the packages. Swordfish steaks stored in CO2-enriched atmospheres had lower total volatile nitrogen (TVN), trimethylamine (TMA) and total volatile acid (TVA) values than steaks stored in air. Oxidative rancidity was not a flavor problem of fish in any of the atmospheres after 20 d of refrigerated storage.