A note on the microbiology of retail packs of prepared salad vegetables

Retail packs of mixed, prepared salad vegetables from two different manufacturers were stored at 7 degrees C until the end of storage-life (sell-by date plus 1 d), when the microbial flora was examined. The quality of the salads was acceptable at the end of storage life. The oxygen concentrations in packs were lower, and the carbon dioxide concentrations were higher, than those in air. High numbers of bacteria were present, with Pseudomonas spp. and Enterobacter agglomerans predominating in packs of both salads, together with lactic acid bacteria in one of the salads. Significant numbers of pectolytic bacteria including Pseudomonas spp. and Erwinia carotovora were detected. Despite the presence of high numbers of coliform bacteria, Escherichia coli was not detected in batches of one salad, and was detected in relatively low numbers in batches of the other. Yersinia spp., predominantly environmental strains of Yersinia enterocolitica, were isolated by enrichment from all samples tested; Staphylococcus aureus and enterococci were not detected.