Development of polymeric and silica filtering materials functionalized with antimicrobial compounds for the elimination of microorganisms in liquid food

Tesis por compendio[ES] En la presente tesis doctoral se ha evaluado el uso de nuevos soportes celulósicos y silíceos como sistemas de filtración para la estabilización y conservación de alimentos líquidos con el fin de afrontar dos grandes retos de la industria de bebidas. Por un lado, evitar o minimizar los cambios en las propiedades nutricionales, estructurales y organolépticas de los alimentos, ocasionados por la pasteurización térmica tradicional, y ofrecer una alternativa al problema de la baja viabilidad debida a los altos costos de inversión/producción al aplicar nuevas tecnologías no térmicas. Por ello, esta tesis doctoral se centra en el desarrollo y evaluación de una nueva tecnología no térmica de conservación de alimentos líquidos basada en la filtración. Se han desarrollado sistemas de filtración a partir de soportes celulósicos y silíceos, sin funcionalizar o funcionalizados con compuestos antimicrobianos. En el primer capítulo se evaluó el uso de materiales de celulosa como soportes filtrantes para el tratamiento de alimentos líquidos. Como primera aproximación se desarrolló un material poroso nano-micro tubular a partir de la extracción y deslignificación del material celulósico presente en el corazón o raquis de la mazorca de maíz. El uso de este soporte resultó ser efectivo como material filtrante para el tratamiento de agua y zumo de naranja, en un sistema de flujo continuo, eliminando la carga microbiana. La aplicación de este soporte como sistema de filtración presenta diversas ventajas como su capacidad de retención microbiana, la reutilización de sub-productos del maíz y, por tanto, su respeto al medioambiente. Sin embargo, sería necesario optimizar el proceso de filtrado para evitar la frecuente obturación de sus poros que requirió varios ciclos de lavado durante el proceso, así como establecer un método de regeneración del material para incrementar su vida útil. Además, este sistema afectó al color del zumo filtrado, que no se mantuvo constante durante el proceso, lo que supone una importante desventaja que es necesaria abordar. Como segunda aproximación, se evaluó el potencial de la inmovilización de una molécula bioactiva sobre membranas de celulosa, para mejorar la capacidad de retención microbiana del material celulósico, así como permitir su reutilización. Los filtros de celulosa funcionalizados con poliaminas demostraron ser eficaces en la eliminación de patógenos en agua, debido a las cargas positivas generadas por los grupos amina inmovilizados en la superficie de las membranas, que atraen y retienen las bacterias cargadas negativamente. Dada la fácil preparación y procedimiento de uso de las membranas de celulosa funcionalizadas con poliaminas, éstas podrían ser consideradas una buena opción para el desarrollo de sistemas de tratamiento de aguas in situ, rápidos, de fácil manejo y de bajo coste. El segundo capítulo describe el desarrollo y aplicación de partículas de sílice funcionalizadas con compuestos de aceites esenciales, con el fin de diseñar coadyuvantes de filtración con actividad antimicrobiana. La filtración de diversas matrices alimentarias (agua, cerveza y zumo de manzana) a través de los soportes funcionalizados con los antimicrobianos naturales demostró ser eficaz en la reducción del recuento de la cepa patógena Escherichia coli, así como frente a la microflora endógena de la cerveza y el zumo (bacterias acidolácticas, aerobios mesófilos, psicrófilos, mohos y levaduras). La eficacia en el control microbiano se debe a la combinación de la adsorción física y la inactivación por contacto con los compuestos de aceites esenciales inmovilizados. Además, la evaluación de las propiedades físico-químicas y sensoriales de los alimentos líquidos demostró un efecto poco significativo, éste depende del tamaño de las partículas de sílice usadas y de la molécula bioactiva inmovilizada. Por lo tanto, el sistema de conservaci�[CA] En la present tesi doctoral s'ha avaluat l'ús de nous suports cel·lulòsics i silicis com a sistemes de filtració per a l'estabilització i conservació d'aliments líquids, amb la finalitat d'afrontar dos grans reptes de la indústria de begudes. D'una banda, evitar o minimitzar els canvis en les propietats nutricionals, estructurals i organolèptiques dels aliments, ocasionats per la pasteurització tèrmica tradicional, i oferir una alternativa al problema de la baixa viabilitat deguda als alts costos d'inversió/producció en aplicar noves tecnologies no tèrmiques. Per això, aquesta tesi doctoral es centra en el desenvolupament i avaluació d'una nova tecnologia no tèrmica de conservació d'aliments líquids basada en la filtració. S'han desenvolupat sistemes de filtració a partir de suports cel·lulòsics i silicis, sense funcionalitzar o funcionalitzats amb compostos antimicrobians. En el primer capítol es va avaluar l'ús de materials de cel·lulosa com a suports filtrants per al tractament d'aliments líquids. Com a primera aproximació es va desenvolupar un material porós nano-micro tubular a partir de l'extracció i deslignificació del material cel·lulòsic present en el cor o raquis de la panolla de dacsa. L'ús d'aquest suport va resultar ser efectiu com a material filtrant per al tractament d'aigua i suc de taronja, en un sistema de flux continu, eliminant la càrrega microbiana. L'aplicació d'aquest suport com a sistema de filtració presenta diversos avantatges com la seua capacitat de retenció microbiana, la reutilització de subproductes de la dacsa i, per tant, el seu respecte al medi ambient. No obstant això, seria necessari optimitzar el procés de filtrat per a evitar la freqüent obturació dels seus porus que va requerir diversos cicles de rentada durant el procés, així com establir un mètode de regeneració del material per a incrementar la seua vida útil. A més, aquest sistema va afectar el color del suc filtrat, que no es va mantenir constant durant el procés, la qual cosa suposa un important desavantatge que és necessari abordar. Com a segona aproximació, es va avaluar el potencial de la immobilització d'una molècula bioactiva sobre membranes de cel·lulosa, per a millorar la capacitat de retenció microbiana del material cel·lulòsic, així com permetre la seua reutilització. Els filtres de cel·lulosa funcionalitzats amb poliamines van demostrar ser eficaces en l'eliminació de patògens en aigua, a causa de les càrregues positives generades pels grups amina immobilitzats en la superfície de les membranes, que atrauen i retenen els bacteris carregats negativament. Donada la fàcil preparació i procediment d'ús de les membranes de cel·lulosa funcionalitzades amb poliamines, aquestes podrien ser considerades una bona opció per al desenvolupament de sistemes de tractament d'aigües in situ, ràpids, de fàcil maneig i de baix cost. El segon capítol descriu el desenvolupament i aplicació de partícules de sílice funcionalitzades amb compostos d'olis essencials, amb la finalitat de dissenyar coadjuvants de filtració amb activitat antimicrobiana. La filtració de diverses matrius alimentàries (aigua, cervesa i suc de poma) a través dels suports funcionalitzats amb els antimicrobians naturals va demostrar ser eficaç en la reducció del recompte del cep patogen Escherichia coli, així com enfront de la microflora endògena de la cervesa i el suc (bacteris àcid làctics, aerobis mesòfils, psicròfils, floridures i llevats). L'eficàcia en el control microbià es deu a la combinació de l'adsorció física i la inactivació per contacte amb els compostos d'olis essencials immobilitzats. A més, l'avaluació de les propietats fisicoquímiques i sensorials dels aliments líquids estudiats va demostrar un efecte poc significatiu, aquest depèn de la grandària de les partícules de sílice usades i de la molècula bioactiva immobilitzada. Per tant, el sistema de conserv[EN] In the present doctoral thesis the use of new cellulosic and silica supports as filtering systems for the stabilization and preservation of liquid foods has been evaluated to overcome two major challenges of the beverage industry. On the one hand, avoid or minimize the changes in the nutritional, structural and organoleptic properties of food caused by traditional thermal pasteurization, and offer an alternative to the problem of low viability due to high investment/production costs when applying new non-thermal technologies. Therefore, this doctoral thesis focuses on the development and evaluation of a new non-thermal technology for the preservation of liquid foods based on filtration. The filtering systems have been developed from cellulosic and silica supports, non-modified or functionalized with antimicrobial compounds. In the first chapter, the use of cellulose materials as filtering supports for the treatment of liquid foods was evaluated. As first approximation, a porous nano-micro tubular material was developed from the extraction and delignification of the cellulosic material present in the corn stalk. The use of this support was effective as filtering material for the treatment of water and orange juice, in a continuous flow system, eliminating the microbial load. The application of this support as filtering system has several advantages, such as its microbial retention capacity, the reuse of corn by-products and, therefore, its respect for the environment. However, it would be necessary to optimize the filtering process to avoid the frequent clogging of its pores that required several washing cycles during the process, as well as to establish a method of material regeneration to increase its life. In addition, this system affected the color of the filtered juice, which did not remain constant during the process, representing an important disadvantage that must be addressed. As a second approach, the potential of the immobilization of a bioactive molecule on cellulose membranes was evaluated to improve the microbial retention capacity of the cellulosic material, as well as to allow its reuse. The cellulose filters functionalized with polyamines proved to be effective in eliminating pathogens in water, due to the positive charges generated by the amine groups immobilized on the surface of the membranes, which attract and retain the negatively charged bacteria. Given the easy preparation and usage of the polyamines-functionalized cellulose membranes, these could be considered a good option for the development of fast, easy to use and low cost in situ water treatment systems. The second chapter describes the development and application of silica particles functionalized with essential oil components to design filtering aids with antimicrobial activity. The filtration of various food matrices (water, beer and apple juice) through the supports functionalized with natural antimicrobials proved to be effective in reducing the load of the pathogenic strain Escherichia coli, as well as reducing the endogenous microflora of beer and the juice (lactic acid bacteria, mesophilic, psychrophilic, mold and yeast). The removal capability is due to the combination of physical adsorption and contact inactivation with the essential oil compounds immobilized. In addition, the evaluation of the physicochemical and sensory properties of the liquid foods studied showed a not significant effect, it depends on the size of the silica particles used and the immobilized bioactive molecule. Therefore, the proposed preservation system has a high potential for cold beverage pasteurization processes.N. Peña-Gomez would like to thank for financial support in the frame of her PhD project to Operational Programme of the European Social Fund (ESF) 2014-2020, the Agencia Estatal de Investigación, Generalitat Valenciana and FEDER-EU (Projects RTI2018-101599-B-C21 and AGL2015-70235-C2-1-R). The authors also thank the Electronic Microscopy & Microanalysis Laboratory at Patras University for support.Peña Gomez, N. (2020). Development of polymeric and silica filtering materials functionalized with antimicrobial compounds for the elimination of microorganisms in liquid food [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/137041TESISCompendi

An overview of emerging trends in pathogen reduction in the processing of fruit juices

Master of ScienceDepartment of Animal Sciences and Industry Food ScienceElizabeth BoyleUnpasteurized fruit juices have been implicated as the source of foodborne outbreaks due to pathogens such as Salmonella, Escherichia coli O157: H7 and Cryptosporidium parvum. The growth of pathogens can usually be slowed through freezing or largely eliminated through pasteurization. Although pasteurization is often effective in eliminating pathogens, it often yields undesirable flavors that are unlike those of fresh juice. Growing consumer trends towards “healthy” unpasteurized alternatives are fueling the development of alternative processing techniques. Several promising techniques for pathogen reduction in the processing of fruit juices are currently being developed. A new technique that is already being marketed worldwide is hyperbaric processing (HPP) which subjects the fruit juice to a high pressure of up to 1000 MPa. The high-pressure treatment results in up to a 7 log reduction kill in pathogens while preserving the naturally occurring flavor profile, sensory attributes and nutritional benefits. Pulsed electric fields (PEF) and ionizing radiation are also being widely explored as viable techniques to process unpasteurized fruit juices. PEF promises to be a commercially viable energy efficient alternative to pasteurization, adding only $0.03 –$0.05 per liter to final food costs. Although irradiation enjoys support for use in the processing of fruit juice by regulatory agencies, support in public opinion is lacking and hinders its growth as an alternative to pasteurization. Other experimental techniques are also present in the development pipeline. Ultrasonic radiation and high intensity pulsed light radiation are both experimental techniques that are being researched. A particularly exciting alternative is the use of plant-based antimicrobials. Several fruits and spices are known to be natural antimicrobials and are therefore being researched as alternatives to the traditional chemical preservatives

Atmospheric Cold Plasma as a Tool for Microbiological Control

Outbreaks of foodborne human illnesses resulting from contaminated raw or minimally processed fruits and vegetables have been widely reported globally. The microbiological challenges associated with fresh produce are diverse and respond differently to minimal processing technologies. Atmospheric cold plasma is a relatively new technology and represents a potential alternative to traditional methods for decontamination of foods. The objective of this work was to determine the influence of extrinsic atmospheric cold plasma (ACP) treatment control parameters and to optimize treatment parameters for decontamination with respect to different forms of key safety challenges pertinent to fresh produce. The optimisation studies demonstrated that inactivation efficacy of treatment, when tested against high populations of E. coli suspended in liquid media, was governed by the processing parameter of mode of exposure, treatment time, post treatment storage time, voltage levels, working gas and media composition. Post treatment storage time emerged as a critical treatment parameter for consistency and efficiency of bacterial inactivation with the system. The effect of media complexity was evident with higher inactivation rates achieved in media with simpler composition. Antimicrobial efficacy of ACP increased when voltage level and gas mixture with higher oxygen content was utilised, nullifying the effect of mode of ACP exposure and media composition. High voltage in-package indirect ACP treatment with 24 h of post treatment storage time, selected as the more favourable treatment approach in terms of produce quality retention, was highly effective for decontamination of cherry tomatoes and strawberries inoculated with Salmonella, E. coli and L. monocytogenes monocultures and against background microflora of produce. However, the produce type and the contaminating pathogen influenced decontaminating effect of ACP with higher inactivation rates achieved for Gram-negative bacteria and bacteria associated with smooth surface of produce. The antimicrobial potential of high voltage either direct or indirect in-package atmospheric air ACP treatment with subsequent 24 h of storage was proven to be effective for inactivation of pathogens in the form of monoculture biofilms commonly implicated in foodborne and healthcare associated human infections, E. coli, L. monocytogenes, S. aureus, P. aeruginosa established during 48 h on abiotic surface. However, the efficiency of ACP treatment was again bacterial type dependant. Although complete inactivation of metabolic activity of Gram-negative bacteria could not be achieved, electron microscopy analyses confirmed the destructive action of ACP treatment. In-package high voltage indirect ACP treatment was effective against Salmonella, L. monocytogenes and E. coli biofilms developed on lettuce. This study also demonstrated that produce storage conditions, such as temperature, light and storage time had interactive effects on bacterial proliferation, internalisation, stress response and susceptibility to the ACP treatment, highlighting the importance of preventive measures as key factors for the assurance of microbiological safety of fresh produce. Significant reductions of P. aeruginosa quorum sensing (QS)-regulated virulence factors, such as pyocyanin and elastase production, were achieved, suggesting that ACP technology could be a potential QS inhibitor and may play an important role in attenuation of virulence of pathogenic bacteria. Despite the varying parameters that influenced plasma bactericidal activity, high voltage in-package atmospheric air ACP decontamination approach showed an efficient reduction of high concentrations of bacteria in liquids, associated with produce and bacteria in their most resistant, biofilm form. These results represent significant technological advances in non-thermal bactericidal treatment with a key advantage of elimination of post-processing contamination of the product, thereby increasing microbiological safety and extension of produce shelf life

Atmospheric Cold Plasma as a Tool for Microbiological Control

Outbreaks of foodborne human illnesses resulting from contaminated raw or minimally processed fruits and vegetables have been widely reported globally. The microbiological challenges associated with fresh produce are diverse and respond differently to minimal processing technologies. Atmospheric cold plasma is a relatively new technology and represents a potential alternative to traditional methods for decontamination of foods. The objective of this work was to determine the influence of extrinsic atmospheric cold plasma (ACP) treatment control parameters and to optimize treatment parameters for decontamination with respect to different forms of key safety challenges pertinent to fresh produce. The optimisation studies demonstrated that inactivation efficacy of treatment, when tested against high populations of E. coli suspended in liquid media, was governed by the processing parameter of mode of exposure, treatment time, post treatment storage time, voltage levels, working gas and media composition. Post treatment storage time emerged as a critical treatment parameter for consistency and efficiency of bacterial inactivation with the system. The effect of media complexity was evident with higher inactivation rates achieved in media with simpler composition. Antimicrobial efficacy of ACP increased when voltage level and gas mixture with higher oxygen content was utilised, nullifying the effect of mode of ACP exposure and media composition. High voltage in-package indirect ACP treatment with 24 h of post treatment storage time, selected as the more favourable treatment approach in terms of produce quality retention, was highly effective for decontamination of cherry tomatoes and strawberries inoculated with Salmonella, E. coli and L. monocytogenes monocultures and against background microflora of produce. However, the produce type and the contaminating pathogen influenced decontaminating effect of ACP with higher inactivation rates achieved for Gramnegative bacteria and bacteria associated with smooth surface of produce. The antimicrobial potential of high voltage either direct or indirect in-package atmospheric air ACP treatment with subsequent 24 h of storage was proven to be effective for inactivation of pathogens in the form of monoculture biofilms commonly implicated in foodborne and healthcare associated human infections, E. coli, L. monocytogenes, S. aureus, P. aeruginosa established during 48 h on abiotic surface. However, the efficiency of ACP treatment was again bacterial type dependant. Although complete inactivation of metabolic activity of Gram-negative bacteria could not be achieved, electron microscopy analyses confirmed the destructive action of ACP treatment. In-package high voltage indirect ACP treatment was effective against Salmonella, L. monocytogenes and E. coli biofilms developed on lettuce. This study also demonstrated that produce storage conditions, such as temperature, light and storage time had interactive effects on bacterial proliferation, internalisation, stress response and susceptibility to the ACP treatment, highlighting the importance of preventive measures as key factors for the assurance of microbiological safety of fresh produce. Significant reductions of P. aeruginosa quorum sensing (QS)-regulated virulence factors, such as pyocyanin and elastase production, were achieved, suggesting that ACP technology could be a potential QS inhibitor and may play an important role in attenuation of virulence of pathogenic bacteria. Despite the varying parameters that influenced plasma bactericidal activity, high voltage in-package atmospheric air ACP decontamination approach showed an efficient reduction of high concentrations of bacteria in liquids, associated with produce and bacteria in their most resistant, biofilm form. These results represent significant technological advances in non-thermal bactericidal treatment with a key advantage of elimination of post-processing contamination of the product, thereby increasing microbiological safety and extension of produce shelf life

Design and Implementation of IGBT Based Power Supply for Food Treatment

Pulsed electric field (PEF) processing has been demonstrated to be an effective non-thermal pasteurization method for food-treatment applications. With this method, high voltage, short-duration pulses are applied to a chamber through which liquid food is passed. If the voltage applied and the corresponding electric field develops a potential higher than a critical trans-membrane potential, the pores expand, and the membrane of the living cell is ruptured. Due to the lower amount of energy consumed during a PEF process, the temperature of the liquid is kept much lower than as opposed to conventional pasteurization. The PEF method thus kills bacteria and other microorganisms while preserving the nutrition and taste of the liquid foods. Although the parameter responsible for inactivation is the voltage applied, for any given voltage, the conductivity of the liquid defines a current through the liquid that causes the temperature to rise. Therefore, preventing excessive heating of the liquid requires the application of an efficient waveform. According to the literature, the most efficient waveform is a square wave since the entire energy applied would be used for the inactivation process. Although some power supplies are capable of generating such a waveform, the generation of an efficient waveform that satisfies all the requirements for producing a viable product for PEF applications is still a challenging problem. In this research, a cascadable pulse generator, based on a Marx generator design, was designed and implemented in order to generate a pulsed waveform for the treatment of liquid food. IGBT switches were used to charge capacitors in parallel and to discharge them in series as a means of generating a high voltage at the output. The design was implemented and tested for two stages, generating up to 6 kV and 1.6 kA square pulses with a controllable pulse width from 1 µs to 10 µs. Up to 3 switches were connected in parallel to enhance the current capability of the system. Also investigated are ways to improve the transient time by enhancing the IGBT driver circuit. The effect of design parameters such as pulse width, voltage, and current on the temperature rise in the liquid was also studied. A variety of liquid foods with different conductivities were tested in order to confirm the functionality of the system

Foodborne Pathogens and Food Safety

Foodborne pathogens represent a major burden on society as they are the cause of high numbers of illnesses, hospitalizations, and deaths each year. In addition to their detrimental impact on human health, these microorganisms, which include pathogenic bacteria, viruses, fungi, and a range of parasites, also represent a significant economic cost to food companies in the implementation and constant oversight of food hygiene and safety programs, product recalls, and potential litigation if outbreaks occur. Advancing our current knowledge of the food processing chain and its vulnerabilities to the many factors related to foodborne pathogens (e.g., their stress response, survival and persistence in processing environments, acquisition of virulence factors and antimicrobial drug resistance) is paramount to the development of effective strategies for early detection and control of pathogens, thereby improving food safety.This Special Issue compiled original research articles contributing to a better understanding of the impact of all aspects of foodborne pathogens on food safety

Salubrité des légumes en conserve par traitement thermique combiné à l'électro-activation : analyse de l'efficacité du système et détermination des économies d'énergie

La salubrité et la qualité des aliments en conserve dépendent toujours des paramètres appliqués lors de la stérilisation (le temps, les températures). L'application de températures élevées peut détériorer la qualité des produits et augmenter les coûts énergétiques associés au procédé de stérilisation. De plus, l’attente des consommateurs se dirige, de nos jours, vers des produits sains et frais, ce qui encourage les chercheurs à découvrir de nouvelles approches et techniques pour améliorer la conservation des aliments. Les technologies émergentes combinées à d'autres approches classiques ont démontré des résultats probants (effet barrière ou «hurdle effect ») quant à la préservation de produits non acidifiés. Récemment, des études sur l'électro-activation (EA) ont mis en évidence son fort potentiel antibactérien applicable pour une large gamme de produits alimentaires. En outre, cette technologie a été reconnue comme étant sécuritaire et peu coûteuse. Le but de ce projet était d'étudier l'EA comme une barrière efficace afin de préserver les qualités nutritionnelles des aliments tout en réduisant les barèmes de stérilisation et les coûts de production dans un respect total de la salubrité du produit. Le premier objectif était d'étudier les propriétés des solutions électro-activées (SEA) ainsi que la dynamique de leurs modifications en fonction de plusieurs paramètres comme la densité de courant appliqué au système, le temps d'excitation, le type de sels utilisés, la concentration en sel et les configurations du réacteur d’électro-activation. De plus, les paramètres optimaux comme le pH, le potentiel redox et la résistance électrique du système, qui est un indice d’efficacité énergétique, ont été déterminés pour la production des SEA à l'aide de la méthode de surface de réponse. Par la suite, les SEA optimisés ont été étudiés sur la corrosivité dans des boîtes de conserve en métal et les résultats obtenus ont montré que la SEA n'a aucun effet significatif sur l'oxydation des contenants de maïs en conserve. Le deuxième objectif a permis de mettre en évidence l'activité sporicide des SEA. En effet, l’étude a montré que les SEA ont une forte capacité d'inhibition de la croissance des spores de Clostridium sporogenes et de Geobacillus stearothermophilus. La combinaison de traitements modérés (T ≤ 100 °C) avec différentes SEA dans la purée de légumes a entraîné une destruction importante ou totale des spores de C. sporogenes. Une diminution considérable de la résistance à la chaleur de G. stearothermophilus a été également observée. Un effet synergique d’une grande efficacité a été obtenu lorsque la SEA a été utilisée en combinaison avec un traitement thermique lors de la stérilisation. Sur le plan pratique, cela résulte en une modification significative des barèmes de stérilisation en utilisant des températures modérées. Le troisième objectif consistait à étudier l'effet combiné des SEA et de la stérilisation à des températures modérées sur la qualité des conserves. Des petits pois et du maïs en grain ont été utilisés comme légumes modèles. L'analyse organoleptique a montré qu'un temps de stérilisation écourté conserve mieux les attributs sensoriels du produit. En plus, les températures de stérilisation utilisées avec les SEA étaient adéquates pour la préservation de la vitamine C qui est utilisée comme indicateur de préservation de la qualité. Aussi, la différence entre la technologie de stérilisation utilisant l’effet combiné de barrières composées de SEA et d’un traitement thermique modéré, comparativement à la technologie de stérilisation classique, laisse entrevoir la possibilité de réaliser d'importantes économies énergétiques. De plus, il sera possible de préserver la qualité nutritionnelle du produit et tout cela sans compromettre sa salubrité. Finalement, ce projet a apporté une contribution significative aux connaissances applicables à l’amélioration de la technologie classique de mise en conserve des légumes via une meilleure compréhension du comportement des spores thermophiles sous l'action des SEA combinées à des températures nettement inférieures à celles utilisées dans le procédé conventionnel de stérilisation des légumes en conserve.The safety and quality of low-acid canned food always depends on the parameters of sterilization. However, high temperatures may lead to a deterioration of product quality and to an increase of energy costs. In addition, today’s the increase of consumer demand for more «fresh-like» foods is challenging researchers to discover innovative approaches and techniques to improve methods of food preservation. Emerging technologies in combination with classical approaches exhibited high effectiveness (hurdle effect) in preservation of low-acid products. Recently, electro-activation (EA) convincing results by demonstrating high antibacterial potential on food products at large scale; furthermore, it has been recognized as a safe and an inexpensive hurdle. Taking sense from the hurdle approach, the aim of this project was to study EA as an effective and potent hurdle, so that it could result in a decrease in sterilization temperatures, thereby decreasing energy costs, increasing food quality and ensuring sterility. The first objective was to study the properties of EA solutions as well as the dynamics of their changes using variety of parameters (current density, excitation time, type and concentration of salts, configurations). In addition, by using the response surface methodology the optimum parameters (pH, redox potential, resistance) for the production of EA solutions (EAS) were found. Thereafter, the optimized EAS were studied for corrosiveness in canned containers showing no significant oxidizing effect on container filled with canned corn which was within the acceptable limits according to the stipulated regulations. The next objective focused on its sporicidal activity. The study showed that EAS has strong inhibiting capacity on the growth of Clostridium sporogenes and Geobacillus stearothermophilus spores. The combination of mild treatments (≤100°C) and EAS in vegetable puree resulted in significant or total destruction of putrefactive spores of C. sporogenes. A considerable decrease in heat-resistance of G. stearothermophilus was also observed. A synergistic effect was observed when EAS was used in combination with heat treatment during sterilisation, which allows changing the temperatures of sterilization. Thus, the last objective investigated the combined effect of EAS and sterilization at mild temperatures on the quality of canned peas and corn. The sensorial analysis showed that a shorter sterilization time increase the preservation of sensorial attributes. Indeed, the lowest temperatures appeared to be more favourable for vitamin C preservation. Nevertheless the difference between classical sterilization and hurdle technologies using EAS displayed significant energy savings and quality preservation. Overall, this project proposed a new approach to improve food canning technology; furthermore, it allowed a better understanding of the thermal behaviour of thermophilic spores under action of EAS as well as expands the scientific knowledge of EA technology

Radiofrequency and Gaseous Technologies for Enhancing the Microbiological Safety of Low Moisture Food Ingredients

High heat resistance and long survival of Salmonella in low moisture food ingredients (LMFIs) such as spices and seeds are concerning as they are typically consumed without cooking. Therefore, it is challenging to effectively inactivate pathogenic bacteria without negatively impacting the quality of the treated product. This dissertation aimed to develop and evaluate novel intervention technologies: in-package radiofrequency steaming and non-thermal gaseous technologies to improve the microbial safety of LMFIs. The dissertation can be divided into three parts. The first part of this dissertation on the thermal inactivation kinetics of Salmonella and a surrogate, Enterococcus faecium NRRL B-2354on black pepper powder indicated that microbial inactivation increased with increasing treatment temperature and water activity. Inoculation protocol also influenced the heat resistance of Salmonella where inoculation of black peppercorns pre-grinding had higher D-values compared to those inoculated post-grinding. The second part of this dissertation aimed at developing an in-package pasteurization process to inactivate Salmonella enterica in spices (black peppercorn) and herbs (dried basil leaves). During RF heating, the one-way steam vent enabled the accumulation of steam inside the package improving the heating uniformity before venting off excess steam. In-package radiofrequency steaming reduced Salmonella below detection levels on dried basil leaves within 35 s in a bottle sealed with a steam vent and 40 s in polymer packages with steam-vent and on black peppercorns within 155 s in a polymer package. A single intervention technology is not fit for all LMF matrices. Thermal processing would not be feasible for chia seeds due to the potential oxidation of fats and gelling in the presence of moisture. Therefore, the third part of the study explored non-thermal antimicrobial gaseous technologies, such as chlorine dioxide (ClO2), and ethylene oxide (EtO) gas on the decontamination of chia seeds. The developed response surface model suggested that an increase in gas concentration, relative humidity, and treatment time enhanced the microbial reduction on chia seeds. At gas concentration of 10 mg/L and 80% RH over a 5 h exposure period; Salmonella and E. faecium populations were reduced by 3.7 ± 0.2 and 3.2 ± 0.3 log CFU/g, respectively. Mild heating at 60 °C after ClO2 (90 %RH, 3 mg/L for 2 h) followed by ambient storage for seven days enhanced the inactivation to achieve 5-log reduction. The quality of treated products was not significantly impacted except for an increase in peroxide value after ClO2 treatment. EtO inactivation was faster than ClO2 treatment on chia seeds providing more than 5 log reduction of Salmonella within 10 minutes at 50% RH and 60 °C without significantly affecting its quality. E. faecium was a suitable surrogate for Salmonella in all intervention technologies investigated in this study. The developed predictive models would benefit food industries in identifying the process parameters for improving LMFIs safety without altering the nutritional and sensorial qualities of food

Radiofrequency and Gaseous Technologies for Enhancing the Microbiological Safety of Low Moisture Food Ingredients

High heat resistance and long survival of Salmonella in low moisture food ingredients (LMFIs) such as spices and seeds are concerning as they are typically consumed without cooking. Therefore, it is challenging to effectively inactivate pathogenic bacteria without negatively impacting the quality of the treated product. This dissertation aimed to develop and evaluate novel intervention technologies: in-package radiofrequency steaming and non-thermal gaseous technologies to improve the microbial safety of LMFIs. The dissertation can be divided into three parts. The first part of this dissertation on the thermal inactivation kinetics of Salmonella and a surrogate, Enterococcus faecium NRRL B-2354on black pepper powder indicated that microbial inactivation increased with increasing treatment temperature and water activity. Inoculation protocol also influenced the heat resistance of Salmonella where inoculation of black peppercorns pre-grinding had higher D-values compared to those inoculated post-grinding. The second part of this dissertation aimed at developing an in-package pasteurization process to inactivate Salmonella enterica in spices (black peppercorn) and herbs (dried basil leaves). During RF heating, the one-way steam vent enabled the accumulation of steam inside the package improving the heating uniformity before venting off excess steam. In-package radiofrequency steaming reduced Salmonella below detection levels on dried basil leaves within 35 s in a bottle sealed with a steam vent and 40 s in polymer packages with steam-vent and on black peppercorns within 155 s in a polymer package. A single intervention technology is not fit for all LMF matrices. Thermal processing would not be feasible for chia seeds due to the potential oxidation of fats and gelling in the presence of moisture. Therefore, the third part of the study explored non-thermal antimicrobial gaseous technologies, such as chlorine dioxide (ClO2), and ethylene oxide (EtO) gas on the decontamination of chia seeds. The developed response surface model suggested that an increase in gas concentration, relative humidity, and treatment time enhanced the microbial reduction on chia seeds. At gas concentration of 10 mg/L and 80% RH over a 5 h exposure period; Salmonella and E. faecium populations were reduced by 3.7 ± 0.2 and 3.2 ± 0.3 log CFU/g, respectively. Mild heating at 60 °C after ClO2 (90 %RH, 3 mg/L for 2 h) followed by ambient storage for seven days enhanced the inactivation to achieve 5-log reduction. The quality of treated products was not significantly impacted except for an increase in peroxide value after ClO2 treatment. EtO inactivation was faster than ClO2 treatment on chia seeds providing more than 5 log reduction of Salmonella within 10 minutes at 50% RH and 60 °C without significantly affecting its quality. E. faecium was a suitable surrogate for Salmonella in all intervention technologies investigated in this study. The developed predictive models would benefit food industries in identifying the process parameters for improving LMFIs safety without altering the nutritional and sensorial qualities of food