Differences in microbiological quality of leafy green vegetables

Abstract

Objective. The aim of the study was to determine the presence and concentration of indicator microorganisms on leafy green vegetables available in Poland. Material and methods. Microbial analyses of 122 samples of leafy green vegetables: rocket, lamb’s lettuce, iceberg lettuce, chive, spinach, celery, dill and parsley, sold in Polish supermarkets in 2018 and 2019, were conducted. The vegetables were analyzed for aerobic mesophilic bacteria, yeasts and moulds, Enterobacteriaceae, Enterococcus, coliforms and Escherichia coli number according to Polish standards. Results. The most microbiologically contaminated vegetables occurred to be parsley, rocket and spinach, and the least contaminated was iceberg lettuce. The presence of total mesophilic bacteria was found in all samples. The highest average number of mesophilic bacteria was found for lamb’s lettuce, rocket, parsley and spinach. Numerous yeasts were presented in almost all leafy green samples while rocket and parsley were the most contaminated with moulds. Enterobacteriaceae were isolated from all samples of parsley. High populations of these bacteria were found in rocket and celery samples. Of the 122 vegetable samples, 95 (78%) were positive for coliforms, especially all samples of parsley were inhabited by these bacteria. 24% of all samples were contaminated by Enterococcus, mainly parsley, spinach and chive. The presence of E. coli was found in only one sample of spinach. Conclusions. The levels of aerobic mesophilic bacteria, yeasts and moulds, Enterobacteriaceae, Enterococcus and coliforms in leafy green vegetables sold in Poland could be classified as moderate or low. The abundant presence of the studied microorganisms may pose a risk for some categories of people consuming leafy green vegetables, mostly immuno-compromised persons.