Microbiological Quality of Nuts, Dried and Candied Fruits, Including the Prevalence of Cronobacter spp.

Anna Berthold-Pluta,Ilona Stefańska,Tamara Aleksandrzak-Piekarczyk,Antoni Pluta,Monika Garbowska,Lidia Stasiak-Różańska

doi:10.3390/pathogens10070900

Abstract

Cronobacter genus bacteria are food-borne pathogens. Foods contaminated with Cronobacter spp. may pose a risk to infants or immunocompromised adults. The aim of this study was to determine the microbiological quality of nuts, seeds and dried fruits with special emphasis on the occurrence of Cronobacter spp. Analyses were carried out on 64 samples of commercial nuts (20 samples), dried fruits (24), candied fruits (8), seeds (4), and mixes of seeds, dried fruits and nuts (8). The samples were tested for the total plate count of bacteria (TPC), counts of yeasts and molds, and the occurrence of Cronobacter spp. Cronobacter isolates were identified and differentiated by PCR-RFLP (Polymerase Chain Reaction - Restriction Fragments Length Polymorphism) and RAPD-PCR (Random Amplified Polymorphic DNA by PCR) analysis. TPC, and yeasts and molds were not detected in 0.1 g of 23.4%, 89.1%, and 32.8% of the analyzed samples. In the remaining samples, TPC were in the range of 1.2–5.3 log CFU g−1. The presence/absence of Cronobacter species was detected in 12 (18.8%) samples of: nuts (10 samples), and mixes (2 samples). The 12 strains of Cronobacter spp. included: C. sakazakii (3 strains), C. malonaticus (5), and C. turicensis (4). The results of this study contribute to the determination of the presence and species identification of Cronobacter spp. in products of plant origin intended for direct consumption.

Highlights

Nuts and dried fruits belong to the category of low moisture food (LMF) [1]
This work was aimed at studying the microbiological quality of commercial ready-toeat food products of plant origin, and at determining the prevalence of Cronobacter spp. in these products with the use of PCR-RFLP (Polymerase Chain Reaction - Restriction Fragments Length Polymorphism), and RAPD-PCR
Presence of Cronobacter spp. in the Tested Food Products and Phenotypic Identification of Twelve samples out of 64 tested (18.8%) classified as nuts and mixtures of seeds, dried fruit and nuts, on the basis of phenotypic characteristics, were considered contaminated with bacteria of the genus Cronobacter, and 12 isolates were isolated from them

Summary

Introduction

Nuts and dried fruits belong to the category of low moisture food (LMF) [1]. Low moisture food products are characterized by extended stability owing to their low water activity (aw ). Ntuli et al [2] and Danyluk et al [3] reported that aw of commercially dried fruits and nuts was approximately 0.78–0.83 and less than. Such a level of aw prevents growth of many pathogens and lends to the microbiological safety of the LMFs. bacteria of the Enterobacteriaceae family (Escherichia coli, Salmonella) cannot propagate on plant products with a low aw , they can remain alive on/in such products for a long time (up to 1 year), especially when products are stored in cold [3,4]

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