We studied microbiological and sensory effects of treating pig tissue for 15 s with 55 and 10°C sprays of acetic acid (AA; 0.15 to 0.3 M) and lactic acid (LA; 0.1 to 0.2 M) solutions prior to the tissue being subjected to steam condensation (18 s at 65°C or 10 s at 75°C). LA or AA spraying and then steam treatment resulted in 3- to 4-log average reductions of Pseudomonas fragi and Yersinia enterocolitica inocula (6 to 7 log CFU/cm(2)), regardless of acid temperature or concentration. Buffered LA or 1:1 mixtures of AA:LA and then steam treatment yielded similar reductions. Most of the acid-steam-treated samples had microbial counts below the limit of detection (2 log CFU/cm(2)); thus, the results likely underestimate the potential of this procedure. When the period between inoculation and acid-steam treatment was extended from 0.5 to 24 h, up to a 1-log-higher microbial reduction was observed, due to a 1- to 2-log-greater initial contamination. Increasing the LA contact time to 6 min increased the microbial reduction by 0.8 log. Acid-steam treatment effected lower L* values (darker color) on pigskin, but higher L* values on muscle and fat tissue (paler color). Many muscle samples exhibited lower a* values and off-color brown hues. Off-odors were observed immediately after treatment, but with the exception of fat tissue and AA-treated samples, they largely disappeared during further storage. Off-flavors were only detected in AA-treated muscle samples.

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Beef has a requirement for refrigerated storage up to 14 d to achieve adequate aging and a tender product. To achieve this aging with little spoilage and no surface drying, vacuum packaging is attractive, because it is inherently simple and offers a clear indication to the packer when the process has failed or there is risk of spoilage. However, there is increasing pressure on the meat industry to limit the use of packaging materials in view of their cost and the cost involved in their recovery and recycling. The purpose of this report was to evaluate an alternative storage system in containers using modified atmospheres at reduced pressure (approximately 25 kPa). The quality of the meat for both container- and vacuum-packed treatments was measured during chilled storage for up to 3 wk. Storage time had the most significant effect on quality characteristics, irrespective of the packaging method. Storage in containers under a 70%N2:30%CO2 gas mixture gave characteristics similar to beef stored under vacuum. Storage in containers under 100% CO2 produced less drip loss than under 70%N2:30%CO2, but generally container storage produced 3 times as much drip loss as vacuum packaging. Shear force of the LM was unaffected by the type of packaging, and at d 2 after slaughter (i.e., before the storage trial was begun), sarcomere lengths of muscles intended for container storage were similar to those destined for vacuum storage. During the packaging treatment, the comparison between the storage systems was always done within 1 animal using one carcass-half for container storage and the other half for vacuum packaging; all bulls were shackled from the left hindleg during bleeding. The majority of the muscles from the left sides had lower shear force values than those from the right sides at the earlier storage times (2 and 9 d after slaughter) but had similar values after longer storage (16 and 23 d after slaughter). This is the first report that shackling beef carcasses from the left side can result in more tender meat in the LM from that side. The increased tenderness in the LM from the shackled side probably resulted from an early decrease in pH and an increase in calpain activity after mechanical strain of the muscles on the shackled side. This effect of shackling should be taken into account when designing systematic comparisons of tenderness in beef.

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The microflora was studied in beef stored in stainless steel containers kept under reduced pressure (20 to 30 kPa) in a modified atmosphere (70% N2 + 30% CO2 or pure CO2) at 3 to 4 degrees C and 0 to 1 degrees C at a headspace:meat volume ratio of 2:1. Samples were obtained at weekly intervals, 1 to 3 times. Total colony counts (TCC) for Pseudomonas spp. and Brochothrix thermosphacta were generally 1 to 2 log10 cfu greater than in the control group of vacuum-packaged beef cuts stored at the same temperatures. In containers with the 70% N2 + 30% CO2 atmosphere at 20 to 30 kPa and 3 to 4 degrees C, substantial growth of Pseudomonas sp. was observed (median of 6 log10 cfu/cm2 at d 21 of storage compared with 3 log10 cfu/cm2 for vacuum-packaged beef). Pseudomonas counts were lower when the container system was held at 0 to 1 degrees C, especially when combined with the pure CO2 atmosphere. As expected for CO2-enriched atmospheres, B. thermosphacta was the dominant spoilage bacterium, in the same log10 order as the TCC. Lowering the storage temperature and changing the atmosphere to pure CO2 resulted in a reduction of 1 log10 for TCC (median values after 2 wk of storage). Although pathogenic bacteria such as Campylobacter, Salmonella, and Listeria monocytogenes were not detected in any sample, further studies are necessary to evaluate potential growth risks. The results demonstrate that CO2-enriched and O2-depleted atmospheres under low pressure have a limited effect on reducing bacterial growth, probably because the antibacterial activity of CO2 is proportional to the effective concentration of this gas in the headspace. At pressures of 20 to 30 kPa, a headspace with pure CO2 would still contain only approximately 20 to 30% CO2.