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      Physiology of the Inactivation of Vegetative Bacteria by Thermal Treatments: Mode of Action, Influence of Environmental Factors and Inactivation Kinetics

      review-article
      * , ,
      Foods
      MDPI
      heat, inactivation, bacteria, sublethal injury, review

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          Abstract

          Heat has been used extensively in the food industry as a preservation method, especially due to its ability to inactivate microorganisms present in foods. However, many aspects regarding the mechanisms of bacterial inactivation by heat and the factors affecting this process are still not fully understood. The purpose of this review is to offer a general overview of the most important aspects of the physiology of the inactivation or survival of microorganisms, particularly vegetative bacteria, submitted to heat treatments. This could help improve the design of current heat processes methods in order to apply milder and/or more effective treatments that could fulfill consumer requirements for fresh-like foods while maintaining the advantages of traditional heat treatments.

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          Most cited references143

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          Biofilm formation and the food industry, a focus on the bacterial outer surface.

          The ability of many bacteria to adhere to surfaces and to form biofilms has major implications in a variety of industries including the food industry, where biofilms create a persistent source of contamination. The formation of a biofilm is determined not only by the nature of the attachment surface, but also by the characteristics of the bacterial cell and by environmental factors. This review focuses on the features of the bacterial cell surface such as flagella, surface appendages and polysaccharides that play a role in this process, in particular for bacteria linked to food-processing environments. In addition, some aspects of the attachment surface, biofilm control and eradication will be highlighted. © 2010 The Authors. Journal compilation © 2010 The Society for Applied Microbiology.
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            On the use of the Weibull model to describe thermal inactivation of microbial vegetative cells.

            This paper evaluates the applicability of the Weibull model to describe thermal inactivation of microbial vegetative cells as an alternative for the classical Bigelow model of first-order kinetics; spores are excluded in this article because of the complications arising due to the activation of dormant spores. The Weibull model takes biological variation, with respect to thermal inactivation, into account and is basically a statistical model of distribution of inactivation times. The model used has two parameters, the scale parameter alpha (time) and the dimensionless shape parameter beta. The model conveniently accounts for the frequently observed nonlinearity of semilogarithmic survivor curves, and the classical first-order approach is a special case of the Weibull model. The shape parameter accounts for upward concavity of a survival curve (beta 1). Although the Weibull model is of an empirical nature, a link can be made with physiological effects. Beta 1 indicates that the remaining cells become increasingly damaged. Fifty-five case studies taken from the literature were analyzed to study the temperature dependence of the two parameters. The logarithm of the scale parameter alpha depended linearly on temperature, analogous to the classical D value. However, the temperature dependence of the shape parameter beta was not so clear. In only seven cases, the shape parameter seemed to depend on temperature, in a linear way. In all other cases, no statistically significant (linear) relation with temperature could be found. In 39 cases, the shape parameter beta was larger than 1, and in 14 cases, smaller than 1. Only in two cases was the shape parameter beta = 1 over the temperature range studied, indicating that the classical first-order kinetics approach is the exception rather than the rule. The conclusion is that the Weibull model can be used to model nonlinear survival curves, and may be helpful to pinpoint relevant physiological effects caused by heating. Most importantly, process calculations show that large discrepancies can be found between the classical first-order approach and the Weibull model. This case study suggests that the Weibull model performs much better than the classical inactivation model and can be of much value in modelling thermal inactivation more realistically, and therefore, in improving food safety and quality.
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              Hfq structure, function and ligand binding.

              Recent studies on Hfq have provided a deeper understanding of the multiple functions of this pleiotropic post-transcriptional regulator. Insights into the mechanism of Hfq action have come from a variety of approaches. A key finding was the characterization of two RNA binding sites: the Proximal Site, which binds sRNA and mRNA; and the Distal Site, which binds poly(A) tails. Hfq was shown to interact with PAP I, PNP and RNase E, proteins that are involved in mRNA decay and in vitro, was shown to form fibres, the physiological significance of which is unknown. Fluorescence resonance energy transfer (FRET) studies directly demonstrated the role of Hfq as a chaperone that facilitates the interaction between sRNAs and target mRNAs. There are still, however, some unresolved questions.
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                Author and article information

                Journal
                Foods
                Foods
                foods
                Foods
                MDPI
                2304-8158
                30 November 2017
                December 2017
                : 6
                : 12
                : 107
                Affiliations
                Tecnología de los Alimentos, Facultad de Veterinaria de Zaragoza, Instituto Agroalimentario de Aragón—IA2, Universidad de Zaragoza-CITA, 50009 Zaragoza, Spain; scondon@ 123456unizar.es (S.C.); manas@ 123456unizar.es (P.M.)
                Author notes
                [* ]Correspondence: guiceb@ 123456unizar.es ; Tel.: +34-976-761-581
                Author information
                https://orcid.org/0000-0002-5049-3646
                Article
                foods-06-00107
                10.3390/foods6120107
                5742775
                29189748
                6bb9c7f4-52f8-4d8c-99c3-7fd194670f44
                © 2017 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 10 October 2017
                : 28 November 2017
                Categories
                Review

                heat,inactivation,bacteria,sublethal injury,review
                heat, inactivation, bacteria, sublethal injury, review

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