Changes in microbial populations in ready-to-eat vegetable salads during shelf-life

The microbiological quality of 56 samples of packaged ready-to-eat vegetable salads was determined during the shelf-life at refrigerated temperature. The analyses included the enumeration and characterization of several microorganisms including total aerobic count, sporeformers, yeasts and moulds, acid lactic bacteria, coliforms, Staphylococcus aureus , Yersinia enterocolitica, Aeromonas spp, Vibrio spp.Pseudomonas spp. The samples were analyzed on the first day on the shelf-life and on the expiry date, 7 days after. In general,the microbiological analysis showed that the samples tested met health and safety conditions. In fact, pathogens such Listeria monocytogenes, Salmonella, Vibrio, Yersinia enterocolitica, Aeromonas spp. were always absent. As regards aerobic colony count, lactic acid bacteria and yeasts, the comparison with international guidelines revealed that all three parameters were satisfactory or acceptable for most samples (about 75%) ; however , considering the results obtained on the last day oh storage , the numbers of unsatisfacoty samples increased during shelf-life. In conclusion, the absence of pathogens and the low incidence of Escherichia coli(CFU/g >102-103 in 7.1%) indicate that in general the samples were in conformity with the conditions for health and safety. However the microbial changes found during storage indicate the need to improve the sanitization and preservation technologies in order to reduce deterioration and possibly increase the shelf-life of the product.