Characterizing the spoilage microbiota of Belgian market fresh-cut iceberg lettuce in controlled atmosphere packaging

Fresh-cut iceberg lettuce is gaining popularity for its convenience, but it is highly susceptible to microbial spoilage. This study aimed to investigate the microbial community dynamics in commercially available fresh-cut iceberg lettuce packaged under controlled atmosphere in Belgium during storage at 7 °C for up to 12 days. To achieve a comprehensive understanding of the spoilage microorganisms and their interactions, a culture-complemented metataxonomic approach was conducted, including plating on non-selective and selective culture media for enumeration of total psychrotrophic counts (TPC), enterobacteria, Pseudomonas spp., psychrotrophic lactic acid bacteria (LAB) and yeasts. Throughout storage, TPC remained the predominant group, followed by Pseudomonas spp. until day 2, and by enterobacteria thereafter. The initial oxygen present in the commercial lettuce bags (1.5-2.0 %) was rapidly consumed within the first 24 h of storage (<0.1 %), resulting in a decrease in the dominance of Pseudomonas spp. (38.9 %) since then. By the end of storage, Pseudomonas spp. represented a minor group (<2 %), yet retained the capacity to grow. In contrast, Lactococcus spp. increased in abundance as CO₂ rose (1.1-25.8 %), eventually dominating the bacterial community (>44 %) together with Serratia (21 %) and Rahnella (9.5-11 %) species. In fact, LAB showed the highest increase in population throughout storage, with levels rising from ∼1.8 log on day 0 to ∼7.5 log colony forming units per gram on day 12. These findings offer new insights into the deterioration mechanisms of fresh-cut lettuce stored under controlled atmosphere packaging, providing a basis for developing new strategies to prevent lettuce spoilage and thereby help the industry and retailers reduce food waste and associated economic losses.