Low water activity foods (LWAF), specifically nuts and dried fruits, have been generally considered safe because they do not support the growth of foodborne pathogens. However, many pathogens have been noted to survive in LWAF for considerable periods of time, and a number of recent outbreaks and recalls have implicated various types of nuts and dried fruits. The Food Safety Modernization Act requires food processors to develop preventive control plans that make ready-to-eat LWAF safer for consumers. The presented research was designed to investigate several aspects of LWAF safety by evaluating a steam process as a strategy to remove pathogen contamination from LWAF, modeling the inactivation of such treatments, and studying the thermal resistances of two E. coli strains in low-water activity solutions. Low-temperature, vacuum-assisted steam (vacuum-steam) was evaluated as a potential intervention and preventive control to remove pathogens from the surface of LWAF without using high-heat treatments that could damage product quality. The presented work examined the efficacy of vacuum-steam (<85°C) as a means to decontaminate the surface of whole macadamia nuts, dried apricot halves, and raisins from Salmonella spp., Listeria monocytogenes, and Shiga toxin-producing Escherichia coli (STEC) contamination. The low-temperature steam treatments successfully reduced all pathogens by >4 log CFU/g from the surfaces of the foods. Additionally, Pediococcus acidilactici, proved to be a surrogate organism for these pathogens and could be used to challenge and validate similar treatments within processing plants. The data were fit to models, which showed that food type significantly impacted the fit, with the Weibull model best describing bacterial inactivation kinetics on raisins and macadamia nuts, and the Gompertz model best describing reductions on the apricot halves. The models were challenged for validation of their abilities to predict times required for 3-log reductions using internal and external datasets, determining the usefulness to industry members who wish to design similar thermal treatments for LWAF. Comparing predicted values from internally constructed models to observed values generated from external data, models were shown to be limited in scope and application and could only be applied to pathogen inactivation on different LWAF or thermal processes in certain circumstances. First-order and Weibull model predictions of bacterial reductions on dried apricots had varied success in predicting times for 3-log reductions on other thermally treated LWAF. However, the models of bacterial reductions on thermally treated macadamia nuts frequently overestimated the times required for 3-log bacterial reductions for other LWAF. In an effort to understand the effect that reduced water activity has specifically on STEC, two strains were investigated for induced thermal resistance due to osmotic stress. Thermal resistance of STEC strains (O121:H19 and O157:H7) were evaluated on the basis of strain variation, culture preparation, and water activity (D- and z-values). At the lowest treatment temperature (56°C), O121 displayed greater heat resistance than O157, and the broth-grown samples exhibited greater heat resistance than the lawn-grown cells, but significant differences were not observed at higher temperatures. Samples in reduced-water activity solutions displayed reduced thermal resistance at 56°C, but the z-values were 29-43% higher than those of high-water activity samples. While water activity has been shown to impact thermal resistance of pathogens, comparisons of STEC thermal resistance according to the D- and z-values revealed that other factors also play roles in pathogen thermal resistance on LWAF. Results from the collection of experiments conclude that efficacy of thermal treatments is impacted by the physiological state of the cells, stress experienced in the food matrix, and characteristics of the food, including water activity and composition. / Doctor of Philosophy / Consumers expect foods they purchase to be safe to consume by themselves and family members, particularly those that are ready-to-eat with no additional cooking requirements. Many of these foods are low-water activity foods (LWAF), like nuts and dried fruits, with very little water content that could be used by bacteria. These foods may be preferred snack foods due to their affordability, long shelf lives, and health benefits over other types of snack foods. Until recently, LWAF were generally considered safe because they do not support the growth of foodborne pathogens due to the lack of moisture or water within the food. However, a number of recent outbreaks related to various types of nuts and dried fruits have proven that many pathogens can survive in dried foods, even if not actively growing, for considerable amounts of time. Designed to address these types of food safety issues, the Food Safety Modernization Act recognizes risks associated with foods and responded with regulations requiring food processors to take steps to make ready-to-eat LWAF, like nuts and dried fruits, safer for consumers. A popular strategy is to treat foods with heat to destroy pathogens, however the quality attributes of some nuts and dried fruits could be damaged by high-heat treatments like roasting. An alternative process uses a vacuum to form steam at lower temperatures, allowing for efficient heat transfer through water droplets to the surface of the foods, thus causing less damage to the foods without introducing too much moisture. This research evaluated how this process could be used by food processors to remove harmful bacteria from the surfaces of whole macadamia nuts, dried apricot halves, and raisins. Results indicated that the low-temperature steam treatments successfully reduced Salmonella, Listeria monocytogenes, and Shiga toxin-producing Escherichia coli (STEC) by >4 log CFU/g (>99.99%) from the surfaces of the foods. Additionally, a nonpathogenic lactic acid bacterium, Pediococcus acidilactici, exhibited similar or greater heat tolerance, which would allow food processors to use it as a substitute, or surrogate, for in-plant studies without introducing harmful bacteria into the food processing environment. Mathematical models were used to describe the trends of bacterial death due to the steam treatments, and the results indicated that the type of food significantly impacted the reduction of bacteria. The models were tested using additional data collected within our own laboratory, as well as others. Results indicated that some of the models could be used as predictors of bacterial death for similar LWAF but can only be applied with caution and consideration for the type of food and process. Additionally, two different E. coli strains associated with outbreaks (O121:H19 and O157:H7) were investigated to understand impacts of strain variation, growth method, and water activity on thermal resistance. Some differences in heat resistance were observed between the strains and between the growth methods. Additionally, the reduced water activity seemed to decrease the bacteria's ability to withstand some heat treatments. Overall, thermal resistance studies indicated that several factors, in addition to water activity, impact pathogens' development of resistance to heat treatments. The experiments' results show that there are complex relationships between bacteria and the food they inhabit. Food processors must consider these relationships in order to design the best thermal processes to make LWAF safe for consumers.

La masse de la baie est le résultat de l’effet intégré de plusieurs facteurs. La recherche a été dessinée afin d’étudier l’effet simultané des facteurs majeurs influençant la masse et la composition de la baie, de les hiérarchiser selon leur degré d’impact à des échelles différentes, de séparer leur effet direct et indirect sur la composition du raisin et de comparer le profil de vins élaborés à partir de petites et grosses baies. L’étude a été conduite sur deux sites expérimentaux, localisés dans les régions de Saint-Emilion (France) et Alcamo (Italie), pendant les années 2014 et 2015. Sur le premier site, les vignes sont plantées sur deux types de sols, tandis que sur le deuxième, deux traitements hydriques étaient appliqués. A l’échelle intra-parcellaire, l’état hydrique de la vigne représente le facteur le plus important, tandis que l’effet du nombre de pépins par baie n’est pas significatif. Des résultats opposés sont obtenus lorsque les relations sont étudiées à l’échelle de la grappe et de la plante. A large échelle, les facteurs impactent directement et indirectement la composition du raisin et les petites baies produisent des moûts et des vins plus concentrés. A l’inverse, à l’échelle de la grappe et de la plante, la masse de la baie n’influence pas la composition du raisin. Seule la concentration en anthocyanes est significativement liée à la masse à toutes les échelles. Cette relation est particulièrement évidente sous conditions hydriques limitantes. Un déficit hydrique augmente le ratio pellicule/pulpe, indépendamment de la masse de la baie. Petites et grosses baies d’une parcelle ayant une condition hydrique homogène, tendent à avoir un profil similaire. / Final berry mass is the result of the integrated effect of several factors. They also influence berry composition. The present work was designed to study the simultaneous effect of major factors influencing berry mass and composition, to hierarchize their impact at different scales, to distinguish their direct and indirect effect on berry composition and to compare the profile of wines made from large and small berries. The study was carried out simultaneously on two vineyards located in the Saint Emil ion (France) and Alcamo (Sicily) areas, during 2014 and 2015. On the first site, vines were planted on two soil types, while on the second site two different irrigation treatments were applied. Depending on the scale, some factors homogeneously impacted the berry mass and composition. At the intra-parcel scale, vine water status represented the most impacting factor, while berry seed number did not have significant effect. Opposite results were obtained when the investigation was carried out at the intra-bunch and intra-plant scales. At large scale, factors impacted directly and indirectly berry compounds and grape juices and wines produced from smaller berries were more concentrated. Neither at intra-bunch, nor at intra-plant scales, berry size effect on juice composition was significant. Only anthocyanin concentration was related to berry size at all scales. This fact was particularly obvious in berries produced under limited water conditions. Water deficit increased the skin to flesh ratio, independently of berry size. This means that small and large berries, produced from a single parcel with homogenous water uptake conditions, tend to have similar enological profiles.

Certains microorganismes qui coexistent sur la vigne, peuvent avoir des effets bénéfiques sur la qualité du vin alors que d'autres peuvent être à l'origine de déviations organoleptiques. Dans la dernière décennie, dans diverses régions viticoles de France, plusieurs odeurs de moisi ou de terre ont été mises en évidence. La (-)-géosmine a été considérée comme étant le principal composé responsable de ce défaut. Des moisissures comme Botrytis cinerea et d'autres appartenant au genre Penicillium ont été souvent isolées à partir des raisins présentant l'odeur " moisi-terreuse ". Les effets de cette molécule sur la qualité des vins a motivé notre étude sur la caractérisation des moisissures responsables de ce défaut organoleptique. A partir d'échantillons prélevés en 2007 en Bourgogne, on a identifié, par des méthodes morphologiques et moléculaires, les moisissures présentes sur les raisins, Une souche de Penicilium expansum (25.03) et deux souches de Botrytis cinerea (BC1 et BC2) ont été sélectionnées. Sur baies de raisin, la validation d'un modèle prédictif des effets combinés de la température et de l'activité de l'eau, sur la croissance des champignons, a pu être mise en oeuvre. Elle a montré, sur de larges gammes de T°C et d'aw, que les modèles cardinaux avec inflexion peuvent être validés sur les produits agro-alimentaires en utilisant le gamma concept. L'étude de l'effet du cuivre sur le taux de croissance radiale et le temps de latence des moisissures, a été entreprise afin de mieux comprendre les mécanismes de résistance au cuivre des champignons et d'en déduire des résultats pour une meilleure efficacité des fongicides. Les moisissures testées ont montré une grande tolérance au cuivre, jusqu'à 4,7 mM pour P. expansum et jusqu'à 8, 2 mM et 7,3 mM respectivement pour B. cinerea, BC1 et BC2. L'étude des effets combinés des facteurs environnementaux et nutritionnels (T°C, CO2; Cu+2) sur la production de géosmine par P. expansum, a conduit à définir les conditions minimisant la production de géosmine. Ainsi, on a pu déterminer que le cuivre (composant actif de nombreux fongicides) est un facteur clé dans la production de géosmine par P. expansum.