New insights into the growth characteristics, bacterial interaction and spoilage contribution of Pseudomonas species in vacuum skin packaged beef

Pseudomonas is generally regarded as a strict aerobe that plays a critical role in aerobically packaged meat spoilage, which has been extensively explored. However, limited information is available about their growth in low-oxygen packaged meat. This study investigated the spoilage characteristics of vacuum skin packaged (VSP) beef steaks associated with microbiota dynamics including Pseudomonas species during chilled storage. Furthermore, the interaction and spoilage contribution of popular Pseudomonas (P. lundensis) and dominant lactic acid bacteria (LAB; Latilactobacillus curvatus) in VSP beef were explored by co-culture and mono-culture. Results demonstrated that Latilactobacillus and Carnobacterium were the predominant bacteria in VSP beef steaks at the end of storage (28 days), but Pseudomonas counts slowly increased during storage (P < 0.05). P. fluorescens subgroup was the main Pseudomonas cluster throughout the entire period, comprising P. azotoformans, P. orientalis, and P. fluorescens, etc. P. azotoformans, P. orientalis, and P. lundensis finally became the most abundant Pseudomonas species. Pseudomonas showed higher spoilage potential than LAB, especially for P. helmanticensis and P. lundensis. In the VSP inoculated beef, P. lundensis and L. curvatus had a competitive interaction and promoted off-odor volatiles (nonanal, acetoin, etc.) production. Albeit the overgrowth of L. curvatus in contrast to P. lundensis occurred in VSP beef, P. lundensis exhibited more robust myofibrillar degradation, accompanied by higher (P < 0.05) pH, total volatile basic nitrogen (TVB-N), and TCA-soluble peptides contents. Therefore, in addition to LAB, the influence of Pseudomonas growth on spoilage and thus on the shelf-life of VSP beef should not be neglected.