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 immunocompromised persons.

Fresh Herbs Addition to Fresh-Cut Iceberg Lettuce: Impact on Quality and Storability

“…The other dominant group of microorganisms were yeasts. According to Kowalska and Szczech [36] their number in iceberg lettuce ranged from 3.4 to 4.0 log10 cfu g -1 , while in other leafy greens the value was higher -about 6.0 log10 cfu g -1 , and these findings are in accordance with presented data. In the case of molds, their number increased during storage especially in control lettuce.…”

“…Jackson et al [41] have found that total cultured bacteria in lettuce and spinach, stored in modified chilled atmosphere increased to 5.5 x 10 8 cfu g -1 . Kowalska and Szczech [36] reported that in leafy vegetables sold in supermarkets, the mesophilic bacteria was the dominant group in all products and reached values as high as 8.4 log10 cfu g -1 , and for iceberg lettuce the bacterial load ranged from 2.08 to 7.16 log10 cfu g -1 . Similarly Sun et al [42] have found that after storage for 3 days the number of bacteria in lettuce increased more than 5 log10 cfu g -1 .…”

“…The strongest increase after herbs application was observed for molds. Kowalska and Szczech [36] reported that among the leafy green vegetables (rocket, spinach, lamb's lettuce, iceberg lettuce, celery, chive, dill, and parsley) the most contaminated vegetables with molds were parsley and rocket, but the least contaminated was iceberg lettuce. This was related to the structure of the plants, as the inner leaves in lettuce heads are less likely to be colonized by microorganisms [37] than the leaves of plants with a spreading, open habit (like parsley and other herbs).…”

Effect of Packaging on Microbial Quality of Edible Flowers During Refrigerated Storage

“…This is because these microorganisms change and accelerate the aging process of stored flowers and can produce volatile compounds responsible for off-flavours and texture changes [Rawat, 2015]. The presence of moulds and yeasts is also undesirable due to their potential adverse effects on human health -some of them (Aspergillus, Penicillium, Alternaria or Fusarium) may produce mycotoxins and others may cause allergies (Cladosporium, Alternaria) [Habibi Najafi & Bahreini, 2012; Kowalska & Szczech, 2022;Tournas, 2005].…”

The Effect of Light Intensity and Photoperiod on the Yield and Antioxidant Activity of Beet Microgreens Produced in an Indoor System

“…According to Kowalska and Szczech [81], assessing the microbiological contamination of vegetables includes determining the levels of Gram-negative bacteria of the Enterobacteriaceae family, with particular relevance to fecal Enterobacteriaceae as general indicators of pollution. The RSA [78] determines that the upper limit value of the microbiological count below which ready-to-eat foods do not represent a health risk corresponds to 5.69 log CFU g −1 .…”