Survival of Listeria monocytogenes, Bacillus cereus and Salmonella Typhimurium on sliced mushrooms during drying in a household food dehydrator

Martin Laage Kragh,Alyssa Marie Caindec,Louisa Obari,Lisbeth Truelstrup Hansen,Hanne Aarslev Jensen

doi:10.1016/j.foodcont.2021.108715

Martin Laage Kragh, Alyssa Marie Caindec + Show 3 more

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https://doi.org/10.1016/j.foodcont.2021.108715

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Journal: Food Control	Publication Date: Apr 1, 2022
Citations: 8	License type: cc-by

Affiliation: Technical University of Denmark

Abstract

The historic view on low-moisture foods (LMFs) as safe due to the lack of microbial growth in these foods is challenged by an increasing number of reports of outbreaks and recalls caused by LMFs contaminated with foodborne pathogens. The objective of this study was to determine the survival of Salmonella Typhimurium , Bacillus cereus and Listeria monocytogenes on sliced Portobello mushrooms ( Agaricus bisporus variant Portobello) during hot-air drying (mushroom internal temperature below 45 °C) for 8 h (h) in a small household food dehydrator (250 W) and subsequent storage of the vacuum-packed dried product for 2 months at room temperature. Hot-air drying reduced the water activity (a w ) of the mushrooms to 0.17 ± 0.03 well below the limit for microbial growth. S. Typhimurium and L. monocytogenes displayed total log CFU reductions of 2.5 ± 0.4 and 2.6 ± 0.8, respectively, while B. cereus exhibited significantly ( p < 0.05) lower log reductions of 1.2 ± 0.1. Storage of vacuum-packed dried mushrooms further reduced L. monocytogenes by 2 log CFU, while numbers of viable S. Typhimurium and B. cereus were not further reduced. The higher stability of S. Typhimurium and B. cereus were reflected in the number of reports in the European Rapid Alert System for Food and Feed system of the presence of these organisms in dried mushrooms. All three organisms regrew to high concentrations when dried mushrooms were soaked overnight at room temperature, simulating a scenario where mushrooms are improperly rehydrated. Combining results from hot-air drying and subsequent storage underlines that hot-air drying and prolonged storage at low a w cannot be relied on alone to reduce the microbial and pathogen load on Portobello mushroom. • Hot-air drying reduced the water activity well below microbial growth limits. • Observed inactivation during drying could not reduce reported mushroom pathogen loads. • B. cereus and S. Typhimurium were stable in stored vacuum packed dried mushrooms. • Foodborne pathogens were able to regrow when dried mushrooms were rehydrated. • Hot-air drying and storage at low a w are not sufficient to ensure safety for dried mushrooms.

Highlights

In recent years there has been an increase in outbreaks or recalls of low-moisture foods (LMFs) contaminated with foodborne pathogens (Beuchat et al, 2013; Sanchez-Maldonado et al, 2018)
The objective of this study was to determine the survival of Salmonella Typhimurium, Bacillus cereus and Listeria monocytogenes on sliced Portobello mushrooms (Agaricus bisporus variant Portobello) during hot-air drying for 8 h (h) in a small household food dehydrator (250 W) and subsequent storage of the vacuum-packed dried product for 2 months at room tem perature
LMFs are defined as foods that are naturally low in moisture or have been through a drying process to lower the water activity below 0.85 to inhibit growth and toxin production of foodborne pathogens (Young et al, 2015)

Summary

Introduction

In recent years there has been an increase in outbreaks or recalls of low-moisture foods (LMFs) contaminated with foodborne pathogens (Beuchat et al, 2013; Sanchez-Maldonado et al, 2018). LMFs are defined as foods that are naturally low in moisture or have been through a drying process to lower the water activity (aw) below 0.85 to inhibit growth and toxin production of foodborne pathogens (Young et al, 2015). Examples of LMF products include cereals, herbs, spices, honey, milk powder, pasta, peanut butter and dried meat, fruit and vegetables that are all considered less vulnerable to growth of foodborne pathogens and spoilage due to the low aw (Podolak et al, 2010). In order to minimize loss of organoleptic properties the tem perature during drying is kept relatively low (40–80 ◦C) with shorter drying times at higher temperatures, which restricts the inactivation of the microbial load present in the food (Bourdoux et al, 2016)

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