A review of quantitative methods to describe efficacy of pulsed light generated inactivation data that embraces the occurrence of viable but non culturable state microorganisms

The purpose of this timely review is to critically appraise and to assess the potential significance of best-published microbial inactivation kinetic data generated by pulsed light (PL). The importance of selecting different inactivation models to describe the PL inactivation kinetics is highlighted. Current methods for the detection of viable-but-nonculturable (VBNC) organisms post PL-treatments are outlined along with the limitations of these methods within food microbiology. Greater emphasis should be placed on elucidating appropriate inactivation kinetic model(s) to cater for the occurrence of these VBNC organisms that are underestimated in number using traditional culture-based enumeration methods. Finally, the importance of further molecular and combinational research to tackle the potential threat posed by VBNC organisms with regard to kinetic inactivation modelling and nexus to public health and food safety is presented.Ciencias de la Alimentació

Influence of food intrinsic factors on the inactivation efficacy of cold atmospheric plasma: Impact of osmotic stress, suboptimal pH and food structure

Cold atmospheric plasma (CAP) has proved to have great potential as a mild food decontamination technology. Different process parameters, including food intrinsic factors, are known to influence the resistance of the cells towards the treatment. The importance of osmotic stress (0, 2, 6% (w/v) NaCl) and suboptimal pH (5.5, 6.5, 7.4) on the CAP efficacy to inactivate Salmonella Typhimurium and Listeria monocytogenes is studied for various food structures. The helium-oxygen plasma was generated by a dielectric barrier discharge reactor, treating samples up to 10min. If grown under osmotic stress or at suboptimal pH, microbial cells adapt and become more resistant during CAP treatment (stress hardening). Additionally, the microorganisms and the food structures also influence the inactivation results. This study illustrates the importance of increasing knowledge on food intrinsic factors, to be able to predict the final CAP inactivation result.publisher: Elsevier articletitle: Influence of food intrinsic factors on the inactivation efficacy of cold atmospheric plasma: Impact of osmotic stress, suboptimal pH and food structure journaltitle: Innovative Food Science & Emerging Technologies articlelink: http://dx.doi.org/10.1016/j.ifset.2016.09.028 content_type: article copyright: © 2016 Published by Elsevier Ltd.status: publishe

Impact of food model (micro)structure on the microbial inactivation efficacy of cold atmospheric plasma

The large potential of cold atmospheric plasma (CAP) for food decontamination has recently been recognized. Room-temperature gas plasmas can decontaminate foods without causing undesired changes. This innovative technology is a promising alternative for treating fresh produce. However, more fundamental studies are needed before its application in the food industry. The impact of the food structure on CAP decontamination efficacy of Salmonella Typhimurium and Listeria monocytogenes was studied. Cells were grown planktonically or as surface colonies in/on model systems. Both microorganisms were grown in lab culture media in petri dishes at 20°C until cells reached the stationary phase. Before CAP treatment, cells were deposited in a liquid carrier, on a solid(like) surface or on a filter. A dielectric barrier discharge reactor generated helium-oxygen plasma, which was used to treat samples up to 10min. Although L. monocytogenes is more resistant to CAP treatment, similar trends in inactivation behavior as for S. Typhimurium are observed, with log reductions in the range [1.0-2.9] for S. Typhimurium and [0.2-2.2] for L. monocytogenes. For both microorganisms, cells grown planktonically are easily inactivated, as compared to surface colonies. More stressing growth conditions, due to cell immobilization, result in more resistant cells during CAP treatment. The main difference between the inactivation support systems is the absence or presence of a shoulder phase. For experiments in the liquid carrier, which exhibit a long shoulder, the plasma components need to diffuse and penetrate through the medium. This explains the higher efficacies of CAP treatment on cells deposited on a solid(like) surface or on a filter. This research demonstrates that the food structure influences the cell inactivation behavior and efficacy of CAP, and indicates that food intrinsic factors need to be accounted when designing plasma treatment.publisher: Elsevier articletitle: Impact of food model (micro)structure on the microbial inactivation efficacy of cold atmospheric plasma journaltitle: International Journal of Food Microbiology articlelink: http://dx.doi.org/10.1016/j.ijfoodmicro.2016.07.024 content_type: article copyright: © 2016 Published by Elsevier B.V.status: publishe

Identification of non-linear microbial inactivation kinetics under dynamic conditions

In this study dynamic microbial inactivation experiments are exploited for performing parameter identification of a non-linear microbial model. For that purpose microbial inactivation data are produced and a differential equation exhibiting a shoulder and a loglinear phase is employed. The derived parameter estimates from this method were used to perform predictions on an independent experimental set at fluctuating temperature. Joint confidence regions and asymptotic confidence intervals of the estimated parameters were compared with previous studies originating from parameter identification under isothermal conditions. The developed approach can provide more reliable estimates for realistic conditions compared to the usual or standard two step approach.[**]status: publishe

Development of a novel approach for secondary modelling in predictive microbiology: incorporation of microbiological knowledge in black box polynomial modelling

This research deals with the development of a novel secondary modelling procedure within the framework of predictive microbiology. The procedure consists of three steps: (i) careful formulation of the available microbiological information, both from literature and from the experimental case study at hand, (ii) translation of these requirements in mathematical terms under the form of partial derivatives throughout the complete interpolation region of the experimental design, and (iii) determination of parameter values with suitable optimisation techniques for a flexible black box modelling approach, e.g., a polynomial model or an artificial neural network model. As a vehicle for this procedure, the description of the maximum specific growth rate of Lactobacillus sakei in modified BHI-broth as influenced by suboptimal temperature, water activity, sodium lactate and dissolved carbon dioxide concentration is under study. The procedure results in a constrained polynomial model with excellent descriptive and interpolating features in comparison with an extended Ratkowsky-type model and classical polynomial model, by combining specific properties of both model types. The developed procedure is illustrated on the description of the lag phase as well. It is stressed how the confrontation with experimental data is very important to appreciate the descriptive and interpolating capacities of new or existing models, which is nowadays not always carefully performed. Alternatively, the first two steps of the novel procedure can be used as a tool to demonstrate clearly (possible) interpolative shortcomings of an existing model with straightforward spreadsheet calculations. (C) 2003 Elsevier B.V. All rights reserved.status: publishe

Combined effect of cold atmospheric plasma, intrinsic and extrinsic factors on the microbial behavior in/on (food) model systems during storage

Microbial decontamination by means of cold atmospheric plasma (CAP) offers great potential for treatment of heat-sensitive food products, extending their storage life. CAP is created by applying a high voltage to a gas stream, resulting in microbial inactivation according to different mechanisms. This paper thoroughly assesses the influence of CAP on the storage life of food model systems inoculated with Salmonella Typhimurium. (Food) model systems, with varying intrinsic factors (pH, salt concentration, and food (micro)structure), are treated for 5 min using a dielectric barrier discharge reactor generating a helium‑oxygen plasma. Following treatment, the impact of extrinsic factors is evaluated by storage at 8 °C or 20 °C. During storage, cell densities are determined. Data are fitted with predictive (growth or inactivation) models. As additional experiments indicate that the CAP treatment itself has a limited or even negligible effect on the properties of the model system (pH, aw, (micro)structure), the microbial behavior of CAP treated samples during storage can be attributed to the treatment. CAP treatment can result in microbial reductions up to 2.7 log10 and prolongs storage, however its rate of success is dependent on both extrinsic and intrinsic factors. An important factor is the storage temperature, as recovery of CAP treated cells proves more difficult when stored at 8 °C. At 20 °C, cell growth is merely slowed down. Additionally, at pH 5.5, 6% (w/v) NaCl, osmotic stress is induced on the microorganisms, which results in low cell recovery or further inactivation. The influence of the food (model) structure on the storage behavior is insignificant.Although being a very promising technology, most studies regarding the use of cold atmospheric plasma (CAP) for food decontamination focus on the inactivation of a target microorganism, in relation to a specific food product. Fundamental knowledge on this non-thermal technology, including its impact on the storage life, is lacking. This study investigates the effect of CAP on the microbial behavior during storage. By performing tests on model systems, for a variation of intrinsic and extrinsic factors, this work renders information on the suitability of this novel technology regarding treatment of a broad spectrum of food products. Moreover, this study demonstrates the limited impact of CAP on the food (model) properties, enhancing the suitability of the technology to be implemented in the food industry.status: publishe

Development of predictive modelling approaches for surface temperature and associated microbiological inactivation during hot dry air decontamination

This research deals with the development of predictive modelling approaches in the field of heat transfer and microbial inactivation. Upon making some backstage microbiological considerations, surface temperature predictions during hot dry air decontaminations are incorporated in a microbial inactivation model, in order to describe inactivation kinetics under realistic (time-varying) temperature conditions. In the present study, the following parts are presented. (i) First, a one-dimensional heat transfer model is developed taking into account exchanges by convection, radiation and evaporation. The model is subsequently validated on a laboratory setup and on a test rig, assuming no water activity changes. This test rig is developed for studying-at a later stage-surface pasteurisation treatment on food products with the use of hot dry air. (ii) Isothermal inactivation data of Escherichia coli K12 MG1655 have been collected and inactivation parameters are accurately estimated by using a primary and a secondary model in a global modelling approach. (iii) Microbiological considerations such as microbial growth effects during come-up times, initial temperature of inactivation, and heat resistance effects, based on experimental observations and on literature studies, are formulated in order to evaluate possible microbial effects arising under the dynamic temperature conditions modelled in step (i). (iv) Microbial inactivation simulations with the incorporation of surface temperature predictions are presented. (v) Finally, the level of the microbial decontamination in an example based on the design of an industrial installation is presented, outlining the importance of the combination of surface temperature and microbial inactivation modelling approaches.status: publishe