Recovery Estimation of Dried Foodborne Pathogens Is Directly Related to Rehydration Kinetics

RESEARCH ARTICLE Recovery Estimation of Dried Foodborne Pathogens Is Directly Related to Rehydration Kinetics Emilie Lang1,2, Fiona Zoz1, Cyril Iaconelli1, Stéphane Guyot1, Pablo Alvarez-Martin2, Laurent Beney1, Jean-Marie Perrier-Cornet1, Patrick Gervais1* 1 Unité Mixte de Recherche—Procédés Alimentaires et Microbiologiques (UMR PAM), Université de Bourgogne Franche-Comté, AgroSup Dijon, 1, Esplanade Erasme, 21000, Dijon, France, 2 Novolyze, 50 rue de Dijon, 21121, Daix, France a11111 * Abstract OPEN ACCESS Citation: Lang E, Zoz F, Iaconelli C, Guyot S, Alvarez-Martin P, Beney L, et al. (2016) Recovery Estimation of Dried Foodborne Pathogens Is Directly Related to Rehydration Kinetics. PLoS ONE 11(8): e0160844. doi:10.1371/journal.pone.0160844 Editor: Anderson de Souza Sant'Ana, University of Campinas, BRAZIL Received: March 11, 2016 Accepted: July 26, 2016 Published: August 5, 2016 Copyright: © 2016 Lang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: Agence Nationale de la Recherche et de la Technologie: The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Novolyze provided support in the form of salaries for authors [EL and PAM] and had a role in decision to publish, but did not have any additional role in the study design, data collection and analysis, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. Drying is a common process which is used to preserve food products and technological microorganisms, but which is deleterious for the cells. The aim of this study is to differentiate the effects of drying alone from the effects of the successive and necessary rehydration. Rehydration of dried bacteria is a critical step already studied in starter culture but not for different kinetics and not for pathogens. In the present study, the influence of rehydration kinetics was investigated for three foodborne pathogens involved in neonatal diseases caused by the consumption of rehydrated milk powder: Salmonella enterica subsp. enterica serovar Typhimurium, Salmonella enterica subsp. enterica serovar Senftenberg and Cronobacter sakazakii. Bacteria were dried in controlled relative humidity atmospheres and then rehydrated using different methods. Our results showed that the survival of the three pathogens was strongly related to rehydration kinetics. Consequently, rehydration is an important step to consider during food safety assessment or during studies of dried foodborne pathogens. Also, it has to be considered with more attention in consumers’ homes during the preparation of food, like powdered infant formula, to avoid pathogens recovery. Introduction Drying is an environmental and technological perturbation involving a water transfer from a liquid state to a gaseous state, following the aW gradient which allows the transformation from a liquid to a solid and dried product. Water activity or aW represents the available water for chemical and biochemical reactions and is theoretically comprised between 0 (no water) and 1 (pure water). During drying, the water activity of products is reduced, preventing bacterial growth and below an aW of 0.6, no microorganisms can grow. This is the reason why drying is a common method used for the preservation of food products or microorganisms of technological interest such as lactic acid and probiotic bacteria. Several methods can be used to reduce aW and, consequently, to dry food or microorganisms. Common drying processes are spraydrying, fluidized bed drying and freeze-drying [1,2] and are used to conserve dried food PLOS ONE | DOI:10.1371/journal.pone.0160844 August 5, 2016 1 / 10 Rehydration of Dried Foodborne Pathogens Competing Interests: EL and PAM are employed by Novolyze. There are no patents, products in development or marketed products to declare. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors. products such as herbs, spices or milk. Moreover, drying has a deleterious effect on cells. Indeed, at the beginning of the drying process, evaporation of water causes an increase in the osmotic pressure of the extracellular medium and, consequently, provokes a large cellular water outflow from the cells creating then an osmotic stress which is damaging for cells [3]. Afterward, in the case of drying conducing to products of low aW, the water removal from extracellular and intracellular media will provoke a direct exposition of cells to oxygen in the air which generates reactive oxygen species in cells and the accumulation of free radicals, creating oxidative stress [3,4]. Damages caused by this stress affect macromolecules and membranes [3,5–9]. Nevertheless, even if drying involves cellular injuries to bacterial cells, dried foods are non-sterilized foods [10] and a large range of microorganisms can survive drying such as fungi, like Aspergillus spores, bacteria, like Salmonella spp., and viruses, like Norovirus [10,11]. Some of them can be dangerous for consumers’ health and this is the reason why a great deal of research is focused on the development of specific decontamination processes [12] for the purpose of achieving a minimal microbial load in dried food according to legal requirements and for consumer health protection. Assessment of microbial survival in dried products involves a rehydration step that is necessary in the method to restore cellular activities, permitting to reach a physiological aW. The influence of this step has already been studied for the optimization of preservation processes of lactic acid bacteria and flora with technological purpose in a dried form [1]. For example, Morgan et al. (2006) reviewed the impact of rehydration of freeze dried lactic acid bacteria and presented it as the final critical step for the revival of cells after drying. Nevertheless, the rehydration kinetics has not been investigated in foodborne pathogens. Moreover, this step has been neglected in the case of pathogens contaminating dried foods or environments. Accordingly, the current method for microbial safety assessment of dried food products is based on their rehydration in a liquid buffer before diluting and spreading for cultivability measurement. However, the rehydration mode, and particularly rehydration kinetics, could drastically impact the cultivability measurement and could lead to erroneous estimation of pathogenic bacteria. This may pose a risk for the consumer due to an underestimation of pathogenic bacteria. Moreover, dried foods are often rehydrated by t (...truncated)