To address the problem of serious microbial spoilage of dark-cutting (DC) beef, this study investigated the changes in the sensory quality, microbial growth, and volatile organic compounds (VOCs) contents of DC beef during storage under mother packaging (MP) consisting of 80% CO₂ and 20% N₂ or 40% CO₂ and 60% N₂, or vacuum packaging (VP) at chilled (4 ℃ ) or superchilled (-1.5 ℃ ) temperature and subsequent display under high-oxygen modified atmosphere packaging (HiOx-MAP) consisting of 60% O₂ and 40% CO₂ at 4 ℃ . The results showed that during superchilled storage, MP significantly inhibited bacterial growth, reduced the contents of certain VOCs (such as hexanal and 1-octen-3-ol), and thus maintained better odor freshness compared to VP; MP with 80% CO₂ concentration showed higher antibacterial effect, and it significantly reduced the concentration of 3-methyl-1-butanol in displayed DC beef steaks while promoting the formation of some VOCs such as diacetyl and hexanal. After storage under high-CO₂ MP, an off-odor was formed, but it disappeared at 15 min after opening the packaging, which did not cause any adverse effects on the freshness. Both CO₂ concentration and VP affected the change of the microbial community during storage. For all packaging treatments, Carnobacterium was the dominant bacteria after display under HiOx-MAP. The growth of Carnobacterium, Serratia and Leuconostoc may be the main cause of off-odor development in DC steaks throughout the storage and display periods. This study recommends the use of storage with 80% CO₂ MP at superchilled temperature and subsequent display under HiOx-MAP to extend the shelflife of DC beef and inhibit spoilage odor due to microbial growth.

Pseudomonas fragi is a predominant meat-borne spoilage bacterium that is sensitive to CO₂ under high-oxygen modified atmosphere packaging (HiOx-MAP). This study was designed to reveal the spoilage potential of a popular wild-type P. fragi T1 in HiOx-MAP beef by whole genome sequencing, and explore the bacterial metabolic response to CO₂ utilizing combined metabolomic and volatile organic compounds (VOCs) analysis, under treatment (CO₂-enriched) HiOx-MAP (TMAP, 50% O₂/40% CO₂/10% N₂) or control (non-CO₂) HiOx-MAP (CMAP, 50% O₂/50% N₂) during chilled storage. Results showed that the strain P. fragi T1 was endued with spoilage-related genes associated with protease, lipase and esterase production, amino acid metabolism, carbon metabolism, sulfur metabolism, and putrescine metabolism, which was responsible for the hydrolysis of meat protein and lipid, as well as off-odor formation. The growth of P. fragi under CMAP resulted in the production of VOCs, such as diacetyl, 1-undecene, 2-undecanone, nonanal, (Z)-5-decen-1-ol, and (E)-2-octenal, etc. The TMAP declined above VOCs concentrations significantly (P < 0.05) by inhibiting P. fragi growth and regulating its metabolic activities. The metabolomic analysis further manifested that CO₂ inhibited the P. fragi growth by decreasing cell membrane fluidity, disturbing energy metabolism, and inhibiting amino acid metabolism and nucleotide biosynthesis. This work provides valuable information for understanding the P. fragi-induced meat spoilage phenomena, and the antibacterial mechanism of CO₂ against P. fragi.