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Secondary growth models from predictive microbiology can describe how the growth rate of microbial populations varies with environmental conditions. Because these models are built based on time and resource consuming experiments, model-based Optimal Experimental Design (OED) can be of interest to reduce the experimental load. In this study, we identify optimal experimental designs for two common models (full Ratkowsky and Cardinal Parameters Model (CPM)) for a different number of experiments (10–30). Calculations are also done fixing one or more model parameters, observing that this decision strongly affects the layout of the OED. Using in silico experiments, we conclude that OEDs are more informative than conventional (equidistant) designs with the same number of experiments. However, OEDs cluster the experiments near the growth limits (X min and X max) resulting in impractical designs with aggregated experimental runs ~10 times longer than conventional designs. To mitigate this, we propose a novel optimality criterion (i.e., the objective function) that accounts for the aggregated time. The novel criterion provides a reduction in parameter uncertainty with respect to the conventional design, without an increase in the experimental load. These results underline that an OED is only based on information theory (Fisher information), so the results can be impractical when actual experimental limitations are considered. The study also emphasizes that most OED schemes identify where to measure, but do not give an indication on how many experiments should be made. In this sense, numerical simulations can estimate the parameter uncertainty that would be obtained for a particular experimental design (OED or not). These results and methodologies (available in Open Code) can guide the design of future experiments for the development of secondary growth models. • Model-based OED identifies the most informative combination of growth experiments. • OEDs for secondary growth models are impractical due to excessive aggregated times. • We define a novel OED including a penalty criterion to make them more practical. • Fixing parameters affects the optimal design scheme and parameter correlation. • OEDs only define where to measure; numerical simulations predict precision. [ABSTRACT FROM AUTHOR]

In the context of ecological transition, the use of wine by-products for industrial applications is a major challenge. Wine lees, the second wine by-product in terms of quantity, represent a source of nutrients that can be used for stimulating the growth of microorganisms. Here, white wine lees were used as a stimulating agent for the growth of wine lactic acid bacteria (LAB) and to promote wine malolactic fermentation (MLF) driven out by Oenococcus oeni. By adding freeze-dried wine lees to wines under different conditions – including different wine lees at different concentrations and different O. oeni strains at various initial populations - it was observed that wine lees can enhance the growth of LAB and reduce the duration of MLF. The chemical composition of wines was also evaluated, proving that wine lees do not compromise the quality of the wines. In addition, wine lees did not seem to promote the growth of spoilage microorganisms like as Brettanomyces bruxellensis. Altogether, this work reports the possibility of recovering the lees of white wine to obtain a product favoring the MLF of red wines. More general, we propose a recycling strategy of wine by-products to obtain new products for winemaking. [Display omitted] • A low-cost culture medium for O. oeni and L. plantarum was developed. • Wine lees promoted MLF performance of O. oeni in synthetic medium and red wines. • 0.5 g/L of wine lees enable MLF with low inoculation rates. • Fruity esters levels increased with the addition of wine lees in wines. • Wine lees did not seem to promote the growth of B. bruxellensis. [ABSTRACT FROM AUTHOR]

Maize moldy and spoilage due to microbial growth is a significant challenge in grain storage. This study aimed to evaluate the effectiveness of a zinc oxide nanocomposite, ZnO@mSiO 2 , prepared in our previous research, in inhibiting mold growth and preserving maize cell quality. The results demonstrated that ZnO@mSiO 2 could effectively inhibit the growth of dominant microorganism, Aspergillus flavus , Talaromyces variabilis , Penicillium citrinum and Fusarium graminearum , in maize storage. Aspergillus flavus was selected as the model fungus, ZnO@mSiO 2 effectively disrupted fungal hyphae structure, leading to reduced hyphal mass and inhibited spore germination. The inhibitory effect of ZnO@mSiO 2 on mold growth was concentration-dependent. However, the ZnO@mSiO 2 at an appropriate concentration (not exceeding 3.0 g/kg) preserved the integrity of maize cell membranes and enhancing the antioxidant activity within maize cells. The findings highlight the potential of ZnO@mSiO 2 as an effective protectant to inhibit mold growth and preserve maize quality during storage. [Display omitted] • ZnO@mSiO 2 demonstrates significant inhibition of bacterial and fungal growth during maize storage. • ZnO@mSiO 2 effectively disrupts fungal mycelial structures. • Optimal concentrations of ZnO@mSiO 2 preserve the integrity of maize cells. • Optimal concentrations of ZnO@mSiO 2 enhance the antioxidant activity of maize cells. [ABSTRACT FROM AUTHOR]

Sourdough starters harbor microbial consortia that benefit the final product's aroma and volume. The complex nature of these spontaneously developed communities raises challenges in predicting the fermentation phenotypes. Herein, we demonstrated for the first time in this field the potential of genome-scale metabolic modeling (GEMs) in the study of sourdough microbial communities. Broad in-silico modeling of microbial growth was applied on communities composed of yeast (Saccharomyces cerevisiae) and different Lactic Acid Bacteria (LAB) species, which mainly predominate in sourdough starters. Simulations of model-represented communities associated specific bacterial compositions with sourdough phenotypes. Based on ranking the phenotypic performances of different combinations, Pediococcus spp. – Lb. sakei group members were predicted to have an optimal effect considering the increase in S. cerevisiae growth abilities and overall CO 2 secretion rates. Flux Balance Analysis (FBA) revealed mutual relationships between the Pediococcus spp. – Lb. sakei group members and S. cerevisiae through bidirectional nutrient dependencies, and further underlined that these bacteria compete with the yeast over nutrients to a lesser extent than the rest LAB species. Volatile compounds (VOCs) production was further modeled, identifying species-specific and community-related VOCs production profiles. The in-silico models' predictions were validated by experimentally building synthetic sourdough communities and assessing the fermentation phenotypes. The Pediococcus spp. – Lb. sakei group was indeed associated with increased yeast cell counts and fermentation rates, demonstrating a 25 % increase in the average leavening rates during the first 10 fermentation hours compared to communities with a lower representation of these group members. Overall, these results provide a possible novel strategy towards the de-novo design of sourdough starter communities with tailored-made characterizations, including a shortened leavening period. • Genome-scale metabolic modeling well-predicted sourdough fermentation phenotypes. • Pediococci and Lb. sakei were correlated with a 25 % increase in leavening rate. • Nutritional bidirectional dependencies and competition shape microbial consortia. • Species and community-related VOCs production patterns were in-silico observed. • The study suggests a novel approach towards tailored sourdough starter communities. [ABSTRACT FROM AUTHOR]

Abstract Listeriosis is a food borne disease associated with high hospitalization and fatality rates; in 2014, EU member states reported 2194 cases with 98.9% hospitalization rates and 210 fatalities. Proper risk analysis and the development of effective food safety strategies critically depend on the knowledge of the growth characteristics of L. monocytogenes on the product in question. Ready-to-eat (RTE) salads present a challenge in this context due to the absence of a heat treatment step before consumption. This study provides challenge-test based data of the growth characteristics of L. monocytogenes on twelve RTE salads. The food matrix, storage time and storage temperature were factors with a significant impact on the growth of L. monocytogenes. While most tested salads permitted a significant increase of L. monocytogenes in at least one of the tested conditions, no growth was observed on celeriac, carrot and corn salad products. There was a considerable increase in growth at 8 °C compared to 5 °C. Our data indicate that the reduction of the storage temperature at retail level to 5 °C and product shelf life could help mitigate the risk of L. monocytogenes in RTE salads. Highlights • The food matrix had a large impact on the growth properties of L. monocytogenes. • Eight RTE salad products supported significant growth of L. monocytogenes. • Celeriac, carrots and corn salad did not support L. monocytogenes growth. • Modelling with Combase was more conservative and did not predict matrix differences. • Storage temperatures of 8 °C resulted in a higher growth potential compared to 5 °C. [ABSTRACT FROM AUTHOR]

Abstract Coupling microbial dynamics with the complete dynamics of the packaging gases is still a challenge. In this work the microbial growth kinetic parameters for Pseudomonas and Lactic Acid Bacteria (LAB) in MAP are identified based on accurate estimation of diffusivity of gases and parameter scaled sensitivity approaches. The microbial dynamics are also compared with those estimated based on partial pressure measurement. Scaled sensitivity coefficient analysis using dissolved gases as variable inputs, shows that in most cases the only coefficients large enough for estimation were those for CO 2max-diss , and for μ max. The current data showed that dissolved gases led significant differences on the microbial parameter of CO 2max values when compared with the headspace gases. On the other hand, the (so-called) dissolved specific growth rate follows a clear trend down for both microorganisms in relation to the increase of the initial headspace CO 2. Finally, current results indicate a possible correlation between CO 2max - diss , CO 2max - headspace , and μ max as functions of CO 2init. [ABSTRACT FROM AUTHOR]

Abstract Many foods and beverages in temperate and tropical regions are prone to contamination by ochratoxin A (OTA), one of the most harmful mycotoxins for human and animal health. Aspergillus ochraceus and Aspergillus carbonarius are considered among the main responsible for OTA contamination. We have previously demonstrated that four low or non- fermenting yeasts are able to control the growth and sporulation of OTA-producing Aspergilli both in vitro and on detached grape berries: the biocontrol effect was partly due to the release of volatile organic compounds (VOCs). Aiming to further characterise the effect of VOCs produced by biocontrol yeast strains, we observed that, beside vegetative growth and sporulation, the volatile compounds significantly reduced the production of OTA by two A. carbonarius and A. ochraceus isolates. Exposure to yeast VOCs also affected gene expression in both species, as confirmed by downregulation of polyketide synthase, non-ribosomal peptide synthase, monooxygenase, and the regulatory genes laeA and veA. The main compound of yeast VOCs was 2-phenylethanol, as detected by Headspace-Solid Phase Microextraction-Gas Chromatography-Tandem Mass Spectrometry (HS-SPME-GC–MS) analysis. Yeast VOCs represent a promising tool for the containment of growth and development of mycotoxigenic fungi, and a valuable aid to guarantee food safety and quality. Highlights • Food and feed can be contaminated by ochratoxin A (OTA) produced by Aspergillus spp. • Non- or low-fermenting yeast selected strains are able to control OTA-producing Aspergillus ochraceus and A. carbonarius. • Yeast volatile organic compounds (VOCs) are responsible for reduction of vegetative growth and sporulation. • Yeast VOCs also reduce OTA production and OTA-biosynthetic gene expression. • The main component of yeast VOCs is 2-phenylethanol. [ABSTRACT FROM AUTHOR]

Traditionally, predictive growth models for food pathogens are developed based on experiments in broth media, resulting in models which do not incorporate the influence of food microstructure. The use of model systems with various microstructures is a promising concept to get more insight into the influence of food microstructure on microbial dynamics. By means of minimal variation of compositional and physicochemical factors, these model systems can be used to study the isolated effect of certain microstructural aspects on microbial growth, survival and inactivation. In this study, the isolated effect on microbial growth dynamics of Listeria monocytogenes of two food microstructural aspects and one aspect influenced by food microstructure were investigated, i.e., the nature of the food matrix, the presence of fat droplets, and microorganism growth morphology, respectively. To this extent, fish-based model systems with various microstructures were used, i.e., a liquid, a second more viscous liquid system containing xanthan gum, an emulsion, an aqueous gel, and a gelled emulsion. Growth experiments were conducted at 4 and 10 °C, both using homogeneous and surface inoculation (only for the gelled systems). Results regarding the influence of the growth morphology indicated that the lag phase of planktonic cells in the liquid system was similar to the lag phase of submerged colonies in the xanthan system. The lag phase of submerged colonies in each gelled system was considerably longer than the lag phase of surface colonies on these respective systems. The maximum specific growth rate of planktonic cells in the liquid system was significantly lower than for submerged colonies in the xanthan system at 10 °C, while no significant differences were observed at 4 °C. The maximum cell density was higher for submerged colonies than for surface colonies. The nature of the food matrix only exerted an influence on the maximum specific growth rate, which was significantly higher in the viscous systems than in the gelled systems. The presence of a small amount of fat droplets improved the growth of L . monocytogenes at 4 °C, resulting in a shorter lag phase and a higher maximum specific growth rate. The obtained results could be useful in the determination of a set of suitable microstructural parameters for future predictive models that incorporate the influence of food microstructure on microbial dynamics. [ABSTRACT FROM AUTHOR]

Building mathematical models in predictive microbiology is a data driven science. As such, the experimental data (and its uncertainty) has an influence on the final predictions and even on the calculation of the model prediction uncertainty. Therefore, the current research studies the influence of both the parameter estimation and uncertainty propagation method on the calculation of the model prediction uncertainty. The study is intended as well as a tutorial to uncertainty propagation techniques for researchers in (predictive) microbiology. To this end, an in silico case study was applied in which the effect of temperature on the microbial growth rate was modelled and used to make simulations for a temperature profile that is characterised by variability. The comparison of the parameter estimation methods demonstrated that the one-step method yields more accurate and precise calculations of the model prediction uncertainty than the two-step method. Four uncertainty propagation methods were assessed. The current work assesses the applicability of these techniques by considering the effect of experimental uncertainty and model input uncertainty. The linear approximation was demonstrated not always to provide reliable results. The Monte Carlo method was computationally very intensive, compared to its competitors. Polynomial chaos expansion was computationally efficient and accurate but is relatively complex to implement. Finally, the sigma point method was preferred as it is (i) computationally efficient, (ii) robust with respect to experimental uncertainty and (iii) easily implemented. [ABSTRACT FROM AUTHOR]

Seafood comprising of both vertebrate and invertebrate aquatic organisms are nutritious, rich in omega-3 fatty acids, essential vitamins, proteins, minerals and form part of healthy diet. However, despite the health and nutritional benefits, seafood is highly perishable. Spoilage of seafood could be as a result of microbial activity, autolysis or chemical oxidation. Microbial activity constitutes more spoilage than others. Spoilage bacteria are commonly Gram negative and produce off odours and flavours in seafood as a result of their metabolic activities. Storage temperature, handling and packaging conditions affect microbial growth and thus the shelf-life of seafood. Due to the complexity of the microbial communities in seafood, culture dependent methods of detection may not be useful, hence the need for culture independent methods are necessary to understand the diversity of microbiota and spoilage process. Similarly, the volatile organic compounds released by spoilage bacteria are not fully understood in some seafood. This review therefore highlights current knowledge and understanding of seafood spoilage microbiota, volatile organic compounds, effects of storage temperature and packaging conditions on quality of seafood. [ABSTRACT FROM AUTHOR]

Gloves are worn by workers harvesting ready-to-eat produce as a deterrent for contaminating the produce with enteric pathogens that may reside on their hands. As fields are not sterile environments, the probability for gloves to become contaminated still exists and therefore it is critical to understand the conditions that affect the survival of pathogens on gloves. Both Escherichia coli O157:H7 and Salmonella deposited on glove surfaces in a liquid state survived longer when the pathogen had been suspended in lettuce sap than when suspended in water. Despite this protection, pathogens deposited on clean single-use gloves were more likely to survive during drying than pathogens deposited on dirty gloves (a film of lettuce sap had been applied to the surface prior to pathogen application and soil had been ground into the gloves). Survival of both E . coli O157:H7 and Salmonella was biphasic with the greatest losses occurring during the first hour of drying followed by much slower losses in the ensuing hours. Pathogens grown in rich media (tryptic soy broth) versus minimal media (M9) as well as those cultured on solid agar versus liquid broth were also more likely to be resistant to desiccation when deposited onto gloves. Although survival of E . coli O157:H7 on nitrile gloves was in general greater than it was on latex gloves, the relative survival of Salmonella on the two glove types was inconsistent. Due to these inconsistencies, no one glove type is considered better than another in reducing the risk for contamination with enteric pathogens. In addition, the extended survival of what are generally referred to as stress-resistant pathogens suggests that gloves either be changed frequently during the day or washed in a disinfectant to reduce the risk of glove contamination that could otherwise contaminate product handled with the contaminated gloves. [ABSTRACT FROM AUTHOR]

Sugar is commonly substituted with stevia-based products in food industry and in our daily-life. This substitution results in a change in food product characteristic formula and properties that may affect the growth dynamics of food pathogenic and spoilage bacteria. This work studies the effect of table sugar (TS), laboratory sucrose (LS), commercial stevia (St) and steviol glycosides (SG) on the growth dynamics of Salmonella Typhimurium and Listeria monocytogenes . Experiments were carried out in general and minimal culture media at 3 equivalent concentration levels in terms of sweetness intensity (TS and LS at 3, 9 and 15% ( w/v ); St at 0.3, 0.9 and 1.5% ( w/v ); and SG at 0.01, 0.03 and 0.05% ( w/v )). Incubation temperatures were: 4, 8 and 20 °C for general media, and for minimal media 20 °C. To decipher the role of these sweeteners, their concentration evolution in minimal media was determined via HPLC analysis. The results revealed slow maximum specific growth rates ( μ max ) of S. Typhimurium in general media with increasing concentrations of TS and LS at 20 °C; and reduced maximum cell population ( N max ) at 8 °C. The growth of L. monocytogenes in general culture media remains invariable independently of the sweetener added, except at 4 °C. At this critical temperature, the presence of TS, LS and St seems to facilitate the growth of L. monocytogenes , presenting higher μ max values in comparison to SG and the control. Varying bacterial response to changes in media formulation suggests that further research is required, focusing on revealing the microbial dynamics in structured media, as well as in real food products. [ABSTRACT FROM AUTHOR]

Gene expression is a fundamentally noisy process giving rise to a significant cell to cell variability at the phenotype level. The phenotypic noise is manifested in a wide range of microbial traits. Heterogeneous behavior of individual cells is observed at the growth, survival and inactivation responses and should be taken into account in the context of Predictive Food Microbiology (PMF). Recent methodological advances can be employed for the study and modeling of single cell dynamics leading to a newgeneration of mechanistic models which can provide insight into the link between phenotype, gene-expression, protein and metabolic functional units at the single cell level. Such models however, need to deal with an enormous amount of interactions and processes that influence each other, forming an extremely complex system. In this review paper, we discuss the importance of noise and present the future challenges in predicting the ?noisy? microbial responses in foods. [ABSTRACT FROM AUTHOR]

The aim of the study was to develop and test the applicability of predictive models for shelf-life estimation of ready-to-eat (RTE) fresh cut salads in realistic distribution temperature conditions in the food supply chain. A systematic kinetic study of quality loss of RTE mixed salad (lollo rosso lettuce-40%, lollo verde lettuce-45%, rocket-15%) packed under modified atmospheres (3% O2, 10% CO2, 87% N2) was conducted. Microbial population (total viable count, Pseudomonas spp., lactic acid bacteria), vitamin C, colour and texture were themeasured quality parameters. Kineticmodels for these indiceswere developed to determine the quality loss and calculate product remaining shelf-life (SLR). Storage experiments were conducted at isothermal (2.5-15 ?C) and nonisothermal temperature conditions (Teff = 7.8 ?C defined as the constant temperature that results in the same quality value as the variable temperature distribution) for validation purposes. Pseudomonas dominated spoilage, followed by browning and chemical changes. The end of shelf-life correlated with a Pseudomonas spp. level of 8 log(cfu/g), and 20% loss of the initial vitamin C content. The effect of temperature on these quality parameters was expressed by the Arrhenius equation; activation energy (Ea) value was 69.1 and 122.6 kJ/mol for Pseudomonas spp. growth and vitamin C loss rates, respectively. Shelf-life prediction models were also validated in real cold chain conditions (including the stages of transport to and storage at retail distribution center, transport to and display at 7 retail stores, transport to and storage in domestic refrigerators). The quality level and SLR estimated after 2-3 days of domestic storage (time of consumption) ranged between 1 and 8 days at 4 ?C andwas predicted within satisfactory statistical error by the kinetic models. Teff in the cold chain ranged between 3.7 and 8.3 ?C. Using the validated models, SLR of RTE fresh cut salad can be estimated at any point of the cold chain if the temperature history is known. Shelf-life models of validated applicability can serve as an effective tool for shelf-life assessment and the development of new products in the fresh produce food sector. [ABSTRACT FROM AUTHOR]

Microbiological limits are widely used in food processing as an aid to reduce the exposure to hazardousmicroorganisms for the consumers. However, in pork, the prevalence and concentrations of Salmonella are generally low and microbiological limits are not considered an efficient tool to support hygiene interventions. The objective of the present studywas to develop an approachwhich couldmake it possible to define potential risk-basedmicrobiological limits for an indicator, enterococci, in order to evaluate the risk frompotential growth of Salmonella. A positive correlation between the concentration of enterococci and the prevalence and concentration of Salmonellawas shown for 6640 pork samples taken at Danish cutting plants and retail butchers. The sampleswere collected in five different studies in 2001, 2002, 2010, 2011 and 2013. The observations that both Salmonella and enterococci are carried in the intestinal tract, contaminate pork by the same mechanisms and share similar growth characteristics (lag phase and maximum specific growth rate) at temperatures around 5-10 ?C, suggest a potential of enterococci to be used as an indicator of potential growth of Salmonella in pork. Elevated temperatures during processingwill lead to growth of both enterococci and, if present, also Salmonella. By combining the correlation between enterococci and Salmonellawith risk modelling, it is possible to predict the risk of salmonellosis based on the level of enterococci. The riskmodel used for this purpose includes the dose-response relationship for Salmonella and a reduction factor to account for preparation of the fresh pork. By use of the riskmodel, it was estimated that themajority of salmonellosis cases, caused by the consumption of pork in Denmark, is caused by the small fraction of pork products that has enterococci concentrations above 5 log CFU/g. This illustrates that our approach can be used to evaluate the potential effect of differentmicrobiological limits and therefore, the perspective of this novel approach is that it can be used for definition of a risk-basedmicrobiological limit for enterococci. The limit for enterococci can then be used for development of a process hygiene criterion in cutting plants and retail butcher shops, with the purpose of reducing the risk of Salmonella for the consumer. [ABSTRACT FROM AUTHOR]

Traditional Italian pork products can be consumed after variable drying periods, where the temporal decrease of water activity spans from optimal to inactivating values. This makes it necessary to A) consider the bias factor when applying culture-medium-based predictive models to sausage; B) apply the dynamic version (described by differential equations) of thosemodels; C) combine growth and deathmodels in a continuousway, including the highly uncertain growth/no growth range separating the two regions. This paper tests the applicability of published predictive models on the responses of Listeria monocytogenes and Yersinia enterocolitica to dynamic conditions in traditional Italian pork sausage, where the environment changes from growth-supporting to inhibitory conditions, so the growth and death models need to be combined. The effect of indigenous lactic acid bacteria was also taken into account in the predictions. Challenge tests were carried out using such sausages, inoculated separately with L. monocytogenes and Y. enterocolitica, stored for 480 h at 8, 12, 18 and 20 ?C. The pH was fairly constant, while the water activity changed dynamically. The effects of the environment on the specific growth and death rate of the studied organisms were predicted using previously published predictive models and parameters. Microbial kinetics inmany productswith a long shelf-life and dynamic internal environment, could result in both growth and inactivation, making it difficult to estimate the bacterial concentration at the time of consumption by means of commonly available predictive software tools. Our prediction of the effect of the storage environment, where the water activity gradually decreases during a drying period, is designed to overcome these difficulties. The methodology can be used generally to predict and visualise bacterial kinetics under temporal variation of environments, which is vital when assessing the safety of many similar products. [ABSTRACT FROM AUTHOR]

Lactic acid bacteria (LAB) are responsible for spoiling vacuum-packedmeat products, such as ham. Since the temperature is the main factor affecting the microbial dynamic, the use of mathematical models describing the microbial behavior into a non-isothermal environment can be very useful for predicting food shelf life. In this study, the growth of Lactobacillus viridescens wasmeasured in vacuum-packed sliced hamunder non-isothermal conditions, and the predictive ability of primary (Baranyi and Roberts, 1994) and secondary (Square Root) models were assessed using parameters estimated in MRS culture medium under isothermal conditions (between 4 and 30 ?C). Fresh ham piece was sterilized, sliced, inoculated, vacuum-packed, and stored in a temperature-controlled incubator at five different non-isothermal conditions (between 4 and 25 ?C) and one isothermal condition (8 ?C). The mathematical models obtained in MRS medium were assessed by comparing predicted values with L. viridescens growth data in vacuum-packed ham. Its predictive ability was assessed through statistical indexes, with good results (bias factor between 0.95 and 1.03; accuracy factor between 1.04 and 1.07, and RMSE between 0.76 and 1.33), especially in increasing temperature, which predictions were safe. The model parameters obtained from isothermal growth data inMRSmedium enabled to estimate the shelf life of a commercial ham under non-isothermal conditions in the temperature range analyzed. [ABSTRACT FROM AUTHOR]

Efficient modelling of the microbial growth rate can be performed by combining the effects of individual conditions in a multiplicative way, known as the gamma concept. However, several studies have illustrated that interactions between different effects should be taken into account at stressing environmental conditions to achieve a more accurate description of the growth rate. In this research, a novel approach for modeling the interactions between the effects of environmental conditions on themicrobial growth rate is introduced. As a case study, the effect of temperature and pH on the growth rate of Escherichia coli K12 is modeled, based on a set of computer controlled bioreactor experiments performed under static environmental conditions. The models compared in this case study are the gamma model, the model of Augustin and Carlier (2000), the model of Le Marc et al. (2002) and the novel multiplicative interaction model, developed in this paper. This novel model enables the separate identification of interactions between the effects of two (or more) environmental conditions. The comparison of thesemodels focuses on the accuracy, interpretability and compatibility with efficient modeling approaches. Moreover, for the separate effects of temperature and pH, new cardinal parameter model structures are proposed. The novel interaction model contributes to a genericmodeling approach, resulting in predictive models that are (i) accurate, (ii) easily identifiable with a limited work load, (iii) modular, and (iv) biologically interpretable. [ABSTRACT FROM AUTHOR]

The inhibitory effect of water activity (aw) and storage temperature on single spore lag times of Aspergillus niger, Eurotium repens (Aspergillus pseudoglaucus) and Penicillium corylophilum strains isolated from spoiled bakery products, was quantified. A full factorial designwas set up for each strain. Datawere collected at levels of aw varying from 0.80 to 0.98 and temperature from 15 to 35 °C. Experiments were performed on malt agar, at pH 5.5. When growthwas observed, ca 20 individual growth kinetics per condition were recorded up to 35 days. Radius of the colony vs time was then fitted with the Buchanan primary model. For each experimental condition, a lag time variability was observed, it was characterized by its mean, standard deviation (sd) and 5th percentile, after a Normal distribution fit. As the environmental conditions became stressful (e.g. storage temperature and aw lower), mean and sd of single spore lag timedistribution increased, indicating longer lag times and higher variability. The relationship betweenmean and sd followed amonotonous but not linear pattern, identicalwhatever the species. Next, secondary models were deployed to estimate the cardinal values (minimal, optimal and maximal temperatures, minimal water activitywhere no growth is observed anymore) for the three species. That enabled to confirm the observation made based on raw data analysis: concerning the temperature effect, A. niger behaviour was significantly different from E. repens and P. corylophilum: Topt of 37.4 °C (standard deviation 1.4 °C) instead of 27.1 °C (1.4 °C) and 25.2 °C (1.2 °C), respectively. Concerning the aw effect, from the three mould species, E. repens was the species able to grow at the lowest aw (awmin estimated to 0.74 (0.02)). Finally, results obtained with single spores were compared to findings from a previous study carried out at the population level (Dagnas et al., 2014). For short lag times (=5 days), there was no difference between lag time of the population (ca 2000 spores inoculated in one spot) and mean (nor 5th percentile) of single spore lag time distribution. In contrast, when lag time was longer, i.e. under more stressful conditions, there was a discrepancy between individual and population lag times (population lag times shorter than 5th percentiles of single spore lag time distribution), confirming a stochastic process. Finally, the temperature cardinal values estimated with single spores were found to be similar to those obtained at the population level, whatever the species. All these findings will be used to describe better mould spore lag time variability and then to predictmore accurately bakery product shelf-life. [ABSTRACT FROM AUTHOR]

In predictive microbiology, the model parameters have been estimated using the sequential two-step modeling (TSM) approach, inwhich primary models are fitted to themicrobial growth data, and then secondarymodels are fitted to the primary model parameters to represent their dependence with the environmental variables (e.g., temperature). The Optimal Experimental Design (OED) approach allows reducing the experimental workload and costs, and the improvement of model identifiability because primary and secondary models are fitted simultaneously from non-isothermal data. Lactobacillus viridescenswas selected to this study because it is a lactic acid bacterium of great interest to meat products preservation. The objectives of this study were to estimate the growth parameters of L. viridescens in culture medium from TSM and OED approaches and to evaluate both the number of experimental data and the time needed in each approach and the confidence intervals of the model parameters. Experimental data for estimating the model parameters with TSM approach were obtained at six temperatures (total experimental time of 3540 h and 196 experimental data of microbial growth). Data for OED approach were obtained from four optimal non-isothermal profiles (total experimental time of 588 h and 60 experimental data of microbial growth), twoprofileswith increasing temperatures (IT) and twowith decreasing temperatures (DT). The Baranyi and Roberts primarymodel and the square root secondarymodelwere used to describe themicrobial growth, inwhich the parameters b and Tmin (?95% confidence interval)were estimated from the experimental data. The parameters obtained from TSM approach were b = 0.0290 (?0.0020) [1/ (h0.5 ?C)] and Tmin = -1.33 (?1.26) [?C], with R2 = 0.986 and RMSE = 0.581, and the parameters obtained with the OED approach were b = 0.0316 (?0.0013) [1/(h0.5 ?C)] and Tmin = -0.24 (?0.55) [?C], with R2 = 0.990 and RMSE= 0.436. The parameters obtained from OED approach presented smaller confidence intervals and best statistical indexes than those fromTSMapproach. Besides, less experimental data and timewere needed to estimate the model parameters with OED than TSM. Furthermore, the OED model parameters were validated with non-isothermal experimental data with great accuracy. In this way, OED approach is feasible and is a very useful tool to improve the prediction of microbial growth under non-isothermal condition. [ABSTRACT FROM AUTHOR]

The limited knowledge concerning the influence of food (micro)structure on microbial dynamics decreases the accuracy of the developed predictive models, asmost studies have mainly been based on experimental data obtained in liquid microbiological media or in/on real foods. The use of model systems has a great potential when studying this complex factor. Apart from the variability in (micro)structural properties, model systems vary in compositional aspects, as a consequence of their (micro)structural variation. In this study, different experimental food model systems, with compositional and physicochemical properties similar to fish patés, are developed to study the influence of food (micro)structure on microbial dynamics. The microbiological safety of fish products is of major importance given the numerous cases of salmonellosis and infections attributed to staphylococcus toxins. The model systems understudy represent food (micro)structures of liquids, aqueous gels, emulsions and gelled emulsions. The growth/inactivation dynamics and a modelling approach of combined growth and inactivation of Salmonella Typhimuriumand Staphylococcus aureus, related to fish products, are investigated in/on thesemodel systems at temperatures relevant to fish products' common storage (4 ?C) and to abuse storage temperatures (8 and 12 ?C). ComBase (http://www.combase.cc/) predictions compared with the maximum specific growth rate (?max) values estimated by the Baranyi and Roberts model in the current study indicated that the (micro)structure influences the microbial dynamics. Overall, ComBase overestimated microbial growth at the same pH, aw and storage temperature. Finally, the storage temperature had also an influence on how much each model system affected the microbial dynamics. [ABSTRACT FROM AUTHOR]

Quantitative microbiology is used in risk assessment studies, microbial shelf life studies, product development, and experimental design. Realistic prediction is, however, complicated by different sources of variability. The final concentration of microorganisms at themoment of consumption is affected by different sources of variability: variability in the storage times and temperatures, variability in product characteristics, variability in process characteristics, variability in the initial contamination of the raw materials, and last but not least, microbiological variability. This article compares different sources of microbiological variability in growth and inactivation kinetics of a pathogen and a spoiler, namely experimental variability, reproduction variability (within strain variability), strain variability (between strain variability) and variability between individual cells within a population (population heterogeneity). Comparison of the different sources of microbiological variability also allows to prioritize their importance. In addition, the microbiological variability is compared to other variability factors encountered in a model food chain to evaluate the impact of different variability factors on the variability in microbial levels encountered in the final product. [ABSTRACT FROM AUTHOR]

Electrospray (ES) is a new non-thermal processing technology for pasteurising liquid foods. This study aimed to investigate the effects of ES on the cell structure and function of Saccharomyces cerevisiae , Escherichia coli and Staphylococcus aureus and then compare the effects of ES and heat treatment (HT) on microbial inactivation and flavour composition in honey raspberry wine. First, we found that the inactivation effect of ES treatment on the three microorganisms was significantly influenced by the voltage intensity. The degree of damage to the cellular structures and functions of the three microorganisms increased with increasing voltage. Second, the environment in which the microorganisms were present significantly influenced the ES pasteurisation effect. Pasteurisation by ES was better when the three microorganisms were in honey raspberry wine than in saline. Finally, the total number of colonies in honey raspberry wine was reduced from 4.50 to 2.03 log colony forming units/mL after ES treatment, and the wine had good stability during storage (84 days at 4 °C). In the honey raspberry wine, the contents of the main flavour substances (ketones and esters) did not change significantly after ES treatment, but HT decreased the content of esters and ketones by 13.5 % and 75.4 %, respectively. • ES disrupted the cell structure and function of S. cerevisiae , E. coli and S. aureus. • ES reduced the total bacterial count of honey raspberry wine by 2.5 log CFU/mL. • The total bacterial count in the ES-treated wine did not increase significantly during the 12-weeks storage (4 °C). • The main flavour substances of the ES-treated wine remained stable during the 12-weeks storage (4 °C). [ABSTRACT FROM AUTHOR]

Gochujang (fermented hot pepper paste) products are well known for their distinct, spicy flavor. However, frequent pack burst spoilage of gochujang products occurs during transportation and storage because of microbial aerogenesis, resulting in considerable economic losses. The present study aimed to prevent pack burst spoilage of gochujang products by supplementing them with garlic ethanol extract. A simulated pack burst experiment revealed that 42.86 % of normal gochujang products were spoiled. Garlic ethanol extract significantly inhibited the growth of Zygosaccharomyces rouxii in gochujang products, with low minimum inhibitory concentration values (12.5–25 mg/mL). Gochujang products supplemented with various concentrations (1 % and 2.5 %) of garlic ethanol extract exhibited marked inhibition of microbial growth, particularly Z. rouxii , and pack burst spoilage. Microbiome analysis revealed that the pack burst samples harbored a high abundance of Z. rouxii. Supplementation of gochujang with 1 % garlic ethanol extract drastically reduced Z. rouxii abundance and prevented pack burst. Moreover, gochujang products supplemented with 1 % garlic ethanol extract exhibited a high hedonic score in the sensory analysis. Based on the results of this study, we concluded that supplementation of gochujang products with 1 % garlic ethanol extract before packaging could be effective in preventing pack burst spoilage of gochujang. • About 43 % (n = 35) of normal gochujang products exhibited pack-burst spoilage. • Zygosaccharomyces rouxii abundance increased in pack-burst gochujang products. • Garlic ethanol extract supplementation inhibited Z. rouxii growth in gochujang. • Garlic ethanol extract supplementation (1 % and 2.5 %) prevented pack burst spoilage. • 1 % of garlic ethanol extract supplemented gochujang harbor high sensory score. [ABSTRACT FROM AUTHOR]

R(+)limonene (LMN) is the major aromatic compound in essential oils obtained from oranges, grapefruits, and lemons. The improvement of preservation techniques to reduce the growth and activity of spoilage microorganisms in foods is crucial to increase their shelf life and to reduce the losses due to spoilage. The aim of this work is to evaluate the effect of LMN on the shelf life of fish fillets. Its effectiveness was preliminarily investigated in vitro against 60 strains of Specific Spoilage Organisms (SSOs) and then on gilt-head sea bream fillets stored at 2 ± 0.5 °C for 15 days under vacuum. LMN showed a good inhibitory effect against tested SSOs strains. On gilt-head sea bream fillets, LMN inhibited the growth SSOs effectively, and its use resulted in a shelf-life extension of ca. 6–9 days of treated fillets, compared to the control samples. The LMN addition in Sparus aurata fillets giving a distinctive smell and like-lemon taste to fish fillets that resulted pleasant to panellists. Its use contributed to a considerable reduction of fish spoilage given that the fillets treated with LMN were still sensory acceptable after 15 days of storage. LMN may be used as an effective antimicrobial system to reduce the microbial growth and to improve the shelf life of fresh gilt-head sea bream fillets. [ABSTRACT FROM AUTHOR]

Chitosan coatings incorporated with 0.5% of oregano and thyme EO were applied onto ready-to-eat peeled shrimp tails and packed under MAP conditions. The growth of naturally present spoilage microorganisms was evaluated for 12 days during chilled storage (4 °C). Coatings containing thyme EO were more effective in inhibiting the microbial species studied, specially lactic acid and psychrotrophic bacteria. As carrier of EOs, chitosan was more effective in inhibiting the growth of bacteria present in peeled shrimps than the direct application of an oil-water (O/W) emulsion. Finally, results from sensory analysis showed that the sensorial quality was affected by the chitosan-thyme coatings despite characteristics like firmness and colour were kept. The present work demonstrates the effectiveness of chitosan enriched coatings, offering a promising alternative to control the growth of spoilage and pathogen microorganisms on peeled shrimps during refrigeration storage. [ABSTRACT FROM AUTHOR]

Proliferation of microbial population on fresh poultry meat over time elicits spoilage when reaching unacceptable levels, during which process slime production, microorganism colony formation, negative organoleptic impact and meat structure change are observed. Spoilage organisms in raw meat, especially Gram-negative bacteria can be difficult to combat due to their cell wall composition. In this study, the natural antimicrobial agents ε-poly- l -lysine (ε-PL) and isoeugenol were tested individually and in combinations for their activities against a selection of Gram-negative strains in vitro. All combinations resulted in additive interactions between ε-PL and isoeugenol towards the bacteria tested. The killing efficiency of different ratios of the two antimicrobial agents was further evaluated in vitro against Pseudomonas putida . Subsequently, the most efficient ratio was applied to a raw turkey meat model system which was incubated for 96 h at spoilage temperature. Half of the samples were challenged with P. putida , and the bacterial load and microbial community composition was followed over time. CFU counts revealed that the antimicrobial blend was able to lower the amount of viable Pseudomonas spp. by one log compared to untreated samples of challenged turkey meat, while the single compounds had no effect on the population. However, the compounds had no effect on Pseudomonas spp. CFU in unchallenged meat. Next-generation sequencing offered culture-independent insight into population diversity and changes in microbial composition of the meat during spoilage and in response to antimicrobial treatment. Spoilage of unchallenged turkey meat resulted in decreasing species diversity over time, regardless of whether the samples received antimicrobial treatment. The microbiota composition of untreated unchallenged meat progressed from a Pseudomonas spp. to a Pseudomonas spp., Photobacterium spp., and Brochothrix thermosphacta dominated food matrix on the expense of low abundance species. We observed a similar shift among the dominant species in meat treated with ε-PL or the antimicrobial blend, but the samples differed markedly in the composition of less abundant species. In contrast, the overall species diversity was constant during incubation of turkey meat challenged with P. putida although the microbiota composition did change over time. Untreated or ε-PL treated samples progressed from a Pseudomonas spp. to a Pseudomonas spp. and Enterobacteriaceae dominated food matrix, while treatment with the antimicrobial blend resulted in increased relative abundance of Hafnia spp., Enterococcaceae , and Photobacterium spp. We conclude that the blend delayed the onset of spoilage of challenged meat, and that all antimicrobial treatments of unchallenged or challenged meat affect the progression of the microbial community composition. Our study confirms that the antimicrobial effects observed in vitro can be extrapolated to a food matrix such as turkey meat. However, it also underlines the consequence of species-to-species variation in susceptibility to antimicrobials, namely that the microbial community change while the CFU remains the same. Addition of antimicrobials may thus prevent the growth of some microorganisms, allowing others to proliferate in their place. [ABSTRACT FROM AUTHOR]

Biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus on food-contact-surfaces represents a significant risk for the public health. In this context, the present study investigates the relationship between the environmental conditions of biofilm formation and the resistance to disinfectants. Therefore, a static biofilm reactor, called NEC-Biofilm System, was established in order to study the effect of growth temperature (20, 30 and 37 °C), and of the surface type (stainless steel and polycarbonate), on biofilm resistance to disinfectants. These conditions were selected to mimic the biofilm formation on abiotic surfaces of food processing industries. The antibiofilm assays were performed on biofilms grown during 24 h. The results showed that the growth temperature influenced significantly the biofilm resistance to disinfectants. These data also revealed that the growth temperature has a significant effect on the biofilm structure of both bacteria. Furthermore, the increase of the biofilm growth temperature increased significantly the algD transcript level in sessile P. aeruginosa cells, whereas the icaA one was not affected in S. aureus cells. Overall, our findings show that the biofilm structure and matrix cannot fully explain the biofilm resistance to disinfectant agents. Nevertheless, it underlines the intimate link between environmental conditions, commonly met in food sectors, and the biofilm resistance to disinfectants. [ABSTRACT FROM AUTHOR]

The enormous potential of multi-omics approaches to unravel microbiome-related links between food quality, sustainability and safety still requires experimental work and extensive data integration to increase knowledge and understand the biological and ecological processes involved in the assembly and dynamics of microbial communities along the production chains. Data spanning from DNA sequences to transcripts and metabolites need to be integrated in order to be translated at industrial level and literature showed several successful examples. The application of microbiome studies in food systems has shown the potential to improve food quality. Nevertheless, classical microbiological methods are still highly relevant even if isolation and characterization of strains in pure culture is often laborious and time-consuming and requires the use of several specific growth media that take into the account microbial growth characteristics as well as food characteristics. Studies on microbiomes have become a popular topic in the food industry since it can be used as a tool to improve quality and safety in the food chain. • Microbial clusters and their interactions are often connected with the final characteristics of the products. • Processing environment is one source of microbes that can easily affect the final structure of the microbiota. • Understanding role, origin and diversity of microbiome increases knowledge with several fields of applications in industry [ABSTRACT FROM AUTHOR]

Prediction of microbial growth kinetics can differ from the actual behavior of the target microorganisms. In the present study, the impact of strain variability on maximum specific growth rate ( μ max ) (h − 1 ) was quantified using twenty Listeria monocytogenes strains. The μ max was determined as function of four different variables, namely pH, water activity (a w )/NaCl concentration [NaCl], undissociated lactic acid concentration ([HA]), and temperature (T). The strain variability was compared to biological and experimental variabilities to determine their importance. The experiment was done in duplicate at the same time to quantify experimental variability and reproduced at least twice on different experimental days to quantify biological (reproduction) variability. For all variables, experimental variability was clearly lower than biological variability and strain variability; and remarkably, biological variability was similar to strain variability. Strain variability in cardinal growth parameters, namely pH min , [NaCl] max, [HA] max , and T min was further investigated by fitting secondary growth models to the μ max data, including a modified secondary pH model. The fitting results showed that L. monocytogenes had an average pH min of 4.5 (5–95% prediction interval (PI) 4.4–4.7), [NaCl] max of 2.0 mM (PI 1.8–2.1), [HA] max of 5.1 mM (PI 4.2–5.9), and T min of − 2.2 °C (PI (− 3.3)–(− 1.1)). The strain variability in cardinal growth parameters was benchmarked to available literature data, showing that the effect of strain variability explained around 1/3 or less of the variability found in literature. The cardinal growth parameters and their prediction intervals were used as input to illustrate the effect of strain variability on the growth of L. monocytogenes in food products with various characteristics, resulting in 2–4 log CFU/ml(g) difference in growth prediction between the most and least robust strains, depending on the type of food product. This underlined the importance to obtain quantitative knowledge on variability factors to realistically predict the microbial growth kinetics. [ABSTRACT FROM AUTHOR]

Lactobacillus plantarum has been associated with food spoilage in a wide range of products and the biofilm growth mode has been implicated as a possible source of contamination. In this study we analysed the biofilm forming capacity of L. plantarum WCFS1 and six food spoilage isolates. Biofilm formation as quantified by crystal violet staining and colony forming units was largely affected by the medium composition, growth temperature and maturation time and by strain specific features. All strains showed highest biofilm formation in Brain Heart Infusion medium supplemented with manganese and glucose. For L. plantarum biofilms the crystal violet (CV) assay, that is routinely used to quantify total biofilm formation, correlates poorly with the number of culturable cells in the biofilm. This can in part be explained by cell death and lysis resulting in CV stainable material, conceivably extracellular DNA (eDNA), contributing to the extracellular matrix. The strain to strain variation may in part be explained by differences in levels of eDNA, likely as result of differences in lysis behaviour. In line with this, biofilms of all strains tested, except for one spoilage isolate, were sensitive to DNase treatment. In addition, biofilms were highly sensitive to treatment with Proteinase K suggesting a role for proteins and/or proteinaceous material in surface colonisation. This study shows the impact of a range of environmental factors and enzyme treatments on biofilm formation capacity for selected L. plantarum isolates associated with food spoilage, and may provide clues for disinfection strategies in food industry. [ABSTRACT FROM AUTHOR]

The practice of freezing food is one of the main processes used by the industry to prolong the shelf life of foods. Its use has expanded in recent years due to the increased consumption of convenience products, many of which are sold in frozen form. The temperature at which these foods are maintained during marketing in supermarkets or stored in the consumer's home is critical to ensure microbiological stability of products. Temperature abuse can allow microbial growth, especially growth of filamentous psychrophilic fungi. Besides economic losses in the industrial sector due to the return of products and loss of confidence by consumers, the development of fungi in foods is a public health problem due to the possibility of mycotoxin production. The aim of this study was to assess the growth at temperatures of 5, 0, − 5 and − 18 °C for two species of fungi involved in the deterioration of frozen chicken nuggets, Penicillium polonicum (33/12 NGT) and Penicillium glabrum (29/12 NGT), inoculated both in culture medium and in the food. The results demonstrated that P. polonicum was able to form microcolonies on potato dextrose agar plates at 0 °C and form visible colonies on the surface of the frozen chicken nuggets kept at − 5 °C for 120 days, regardless of brand. For P. glabrum the limiting growth temperature was 5 °C in the culture medium and 0 °C on frozen chicken nuggets, regardless of the brand analyzed. Thus, it is essential to adhere to the storage temperatures recommended to ensure the stability and safety of this food product. [ABSTRACT FROM AUTHOR]

Microorganisms rarely live in isolation but are most often found in a consortium. This provides the potential for cross-feeding and nutrient competition among the microbial species, which make it challenging to predict the growth kinetics in coculture. In this paper we developed a mathematical model to describe substrate consumption and subsequent microbial growth and metabolite production for bacteria grown in monoculture. The model characterized substrate utilization kinetics of 18 Bifidobacterium strains. Some bifidobacterial strains demonstrated preferential degradation of oligofructose in that sugars with low degree of polymerization (DP) (DP ≤ 3 or 4) were metabolized before sugars of higher DP, or vice versa. Thus, we expanded the model to describe the preferential degradation of oligofructose. In addition, we adapted the model to describe the competition between human colonic bacteria Bacteroides thetaiotaomicron LMG 11262 and Bifidobacterium longum LMG 11047 or Bifidobacterium breve Yakult for inulin as well as cross-feeding of breakdown products from the extracellular hydrolysis of inulin by B. thetaiotaomicron LMG 11262. We found that the coculture growth kinetics could be predicted based on the respective monoculture growth kinetics. Using growth kinetics from monoculture experiments to predict coculture dynamics will reduce the number of in vitro experiments required to parameterize multi-culture models. [ABSTRACT FROM AUTHOR]

Chitosan/cyclodextrin films (CS:CD) incorporating carvacrol were obtained by casting, and conditioned at 23 °C and 75% relative humidity prior to being immersed in liquid carvacrol until they reached sorption equilibrium. In a previous work, the in vitro antimicrobial activity of these films was studied. In this work, active films were used to inhibit microbial growth in packaged chicken breast fillets. Samples of CS:CD films loaded with carvacrol, of different sizes and thus with different quantities of antimicrobial agent, were stuck to the aluminium lid used to seal PP/EVOH/PP cups containing 25 g of chicken fillets. These samples were stored for 9 days at 4 °C. The packages were hermetically sealed and it was confirmed that they provided an infinite barrier to carvacrol. The partition of the antimicrobial agent within the food/packaging system was analysed. The antimicrobial devices rapidly released a large percentage of the agent load, amounts that were gained by the adhesive coating of the lid and especially by the chicken fillets. The latter were the main sorbent phase, with average concentrations ranging between 200 and 5000 mg/Kg during the period of storage. The microbiota of the packaged fresh chicken fillets - mesophiles, psychrophiles, Pseudomonas spp., enterobacteria, lactic acid bacteria and yeasts and fungi - were analysed and monitored during storage. A general microbial inhibition was observed, increasing with the size of the active device. Inhibition with a 24 cm² device ranged from 0.3 log reductions against lactic acid bacteria to 1.8 logs against yeasts and fungi. However, the large amount of antimicrobial that was sorbed or that reacted with the fillet caused an unacceptable sensory deterioration. These high sorption values are probably due to a great chemical compatibility between chicken proteins and carvacrol. [ABSTRACT FROM AUTHOR]

Spoilage of chocolate pralines, due to growth of microorganisms tolerating low water activity, causes problems in the confectionary industry. Therefore, an increased knowledge on which organisms are present in the chocolate fillings and their tolerance towards low aw, pH, ethanol and other preservatives is needed. Using media containing 40-50% glucose (aw 0.872-0.925) bacteria, yeasts and moulds were isolated from chocolate pralines (aw 0.70-0.898) of nine manufactures and sugar syrups (aw 0.854) used as ingredient in chocolate praline production by one of the manufacturers. Isolates were identified by conventional microbiological analyses and by sequencing of their 16S rRNA, 26S rRNA (D1/D2-region) or calmodulin genes. Further, for several species the identity was confirmed by amplification and sequencing of additional genes. In total 677 isolates were identified as belonging to ten different bacteria species, six yeast species and ten mould species with yeast being the most frequently isolated. Bacteria and moulds were found in low numbers, whereas yeast were found in numbers up to 107CFU/g. The most frequently isolated yeast, bacteria and moulds belonged to the species of Zygosaccharomyces rouxii, Bacillus subtilis and Aspergillus terreus, respectively. Fifteen isolates were screened for their ability to grow in presence of low aw (0.65-0.90), low pH (pH=2.0-7.0), ethanol (0-15%), sorbic acid (0-1500ppm) and different temperatures (15°C-25°C) relevant for chocolate manufacturing. Z. rouxii was overall the most tolerant organism to the stress factors and grew within the same range of environmental conditions as found in chocolate pralines. It was able to grow at water activities down to 0.70, ethanol concentrations up to 6.0%, pH down to pH2.0, sorbic acid concentrations up to 1500ppm and at all temperatures tested. Eurotium amstelodami also showed high tolerance towards all the stress factors except for ethanol. None of the bacteria were able to grow at the conditions tested. However, B. subtilis survived the 60day incubation period. [ABSTRACT FROM AUTHOR]

Abstract: Deterministic models describing heat transfer and microbial growth in the cold chain are widely studied. However, it is difficult to apply them in practice because of several variable parameters in the logistic supply chain (e.g., ambient temperature varying due to season and product residence time in refrigeration equipment), the product's characteristics (e.g., pH and water activity) and the microbial characteristics (e.g., initial microbial load and lag time). This variability can lead to different bacterial growth rates in food products and has to be considered to properly predict the consumer's exposure and identify the key parameters of the cold chain. This study proposes a new approach that combines deterministic (heat transfer) and stochastic (Monte Carlo) modeling to account for the variability in the logistic supply chain and the product's characteristics. The model generates a realistic time-temperature product history , contrary to existing modeling whose describe time-temperature profile Contrary to existing approaches that use directly a time-temperature profile, the proposed model predicts product temperature evolution from the thermostat setting and the ambient temperature. The developed methodology was applied to the cold chain of cooked ham including, the display cabinet, transport by the consumer and the domestic refrigerator, to predict the evolution of state variables, such as the temperature and the growth of Listeria monocytogenes. The impacts of the input factors were calculated and ranked. It was found that the product's time-temperature history and the initial contamination level are the main causes of consumers' exposure. Then, a refined analysis was applied, revealing the importance of consumer behaviors on Listeria monocytogenes exposure. [Copyright &y& Elsevier]

Abstract: Proto-cooperation between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus is one of the key factors that determine the fermentation process and final quality of yoghurt. In this study, the interaction between different proteolytic strains of S. thermophilus and L. delbrueckii subsp. bulgaricus was investigated in terms of microbial growth, acidification and changes in the biochemical composition of milk during set-yoghurt fermentation. A complementary metabolomics approach was applied for global characterization of volatile and non-volatile polar metabolite profiles of yoghurt associated with proteolytic activity of the individual strains in the starter cultures. The results demonstrated that only non-proteolytic S. thermophilus (Prt−) strain performed proto-cooperation with L. delbrueckii subsp. bulgaricus. The proto-cooperation resulted in significant higher populations of the two species, faster milk acidification, significant abundance of aroma volatiles and non-volatile metabolites desirable for a good organoleptic quality of yoghurt. Headspace SPME-GC/MS and 1H NMR resulted in the identification of 35 volatiles and 43 non-volatile polar metabolites, respectively. Furthermore, multivariate statistical analysis allows discriminating set-yoghurts fermented by different types of starter cultures according to their metabolite profiles. Our finding underlines that selection of suitable strain combinations in yoghurt starters is important for achieving the best technological performance regarding the quality of product. [Copyright &y& Elsevier]

The influence of growth temperature (10, 25, 37, and 42°C) on the survival of Salmonella Enteritidis in simulated gastric fluid (SGF; pH=2.0) and during heat treatment (54, 56, 58, and 60°C), on the membrane fatty acid composition, as well as on stress-/virulence-related gene expression was studied. Cells incubated at temperatures lower or higher than 37°C did not increase their acid resistance, with the maximum D-value of 3.07min in cells grown at 37°C; while those incubated at higher temperature increased their heat resistance, with the maximum D 60°C-values of 1.4min in cells grown at 42°C. A decrease in the ratio of unsaturated to saturated fatty acids was observed as the growth temperature increased. Compared to the control cells grown at 37°C, the expression of rpoS was 16.5- and 14.4-fold higher in cells cultivated at 10 and 25°C, respectively; while the expression of rpoH was 2.9-fold higher in those cultivated at 42°C. The increased expression of stress response gene rpoH and the decreased ratio of unsaturated to saturated fatty acids correlated with the greater heat resistance of bacteria grown at 42°C; while the decreased expression of stress response gene rpoS at 42°C might contribute to the decrease in acid resistance. Virulence related genes-spvR, hilA, avrA-were induced in cells cultivated at 42°C, except sefA which was induced in the control cells. This study indicates that environmental temperature may affect the virulence potential of S. Enteritidis, thus temperature should be well controlled during food storage. [ABSTRACT FROM AUTHOR]

Abstract: Non-Saccharomyces yeasts include different species which comprise an ecologically and biochemically diverse group capable of altering fermentation dynamics and wine composition and flavour. In this study, single- and mixed-culture of Hanseniaspora guilliermondii and Saccharomyces cerevisiae were used to ferment natural grape-juice, under two nitrogen regimes. In single-culture the strain H. guilliermondii failed to complete total sugar breakdown even though the nitrogen available has not been a limiting factor of its growth or fermentative activity. In mixed-culture, that strain negatively interfered with the growth and fermentative performance of S. cerevisiae, resulting in lower fermentation rate and longer fermentation length, irrespective of the initial nitrogen concentration. The impact of co-inoculation on the volatile compounds profile was more evident in the wines obtained from DAP-supplemented musts, characterised by increased levels of ethyl and acetate esters, associated with fruity and floral character of wines. Moreover, the levels of fatty acids and sulphur compounds which are responsible for unpleasant odours that depreciate wine sensory quality were significantly lower. Accordingly, data obtained suggests that the strain H. guilliermondii has potential to be used as adjunct of S. cerevisiae in wine industry, although possible interactions with S. cerevisiae still need to be elucidated. [Copyright &y& Elsevier]

This study aims to quantify growth and cereulide production by Bacillus cereus and their potential correlation in an intermediate dairy wet-mix. Systematic experiments were carried out using the emetic reference strain F4810/72 in the suboptimal range of temperature of 12 °C to 20 °C. Growth and cereulide kinetic parameters were estimated and the three parameters (i) time to first cereulide quantification (t cer), (ii) maximum specific growth rates (μ max) and (iii) cereulide production rates (k) were modelled as a function of temperature. As temperature increased, growth lag time and t cer were shorter while microbial increase and cereulide production happened earlier, and at higher rates. Maximum concentration of cells and maximum cereulide concentration proved to be temperature-independent, reaching the average values of 7.9 ± 0.3 log 10 (CFU/mL) and 2.6 ± 0.2 log 10 (ng.g−1) respectively. Moreover, the time to reach the widely used threshold of 5 log 10 CFU/mL (t 5log) was tested against t cer , and this suggested that this threshold can be used with increased confidence at lower temperatures to assure toxin is not quantified in this matrix. The average t cer were equal to 314 h, 118 h, 73 h and 45 h for 12 °C, 15 °C, 18 °C and 20 °C respectively. A validation study was performed using independent data sets obtained with the same strain in other dairy matrices. The microbial growth models presented good predictive power even when extrapolated beyond the temperature range of construction. Nevertheless, the models proposed for prediction of toxin production over time presented limitations, especially for food matrices that deviate significantly from the original matrix for which the model was developed, making cereulide predictions less accurate. Our findings suggest that similar modelling approaches can be used to predict growth, time to first cereulide quantification as well as cereulide formation over time for a specific matrix, but that matrix-extrapolations are more suitable for growth than for cereulide. • Time to reach 5 log CFU/mL was correlated to time to first cereulide quantification • As temperature decreases, log counts were higher at cereulide quantification point • Growth model developed in dairy wet-mix predicted well μ max in other dairy matrices • Limited extrapolations between matrices were possible for cereulide prediction [ABSTRACT FROM AUTHOR]

The foodborne pathogen Listeria monocytogenes has the ability to produce biofilms in food-processing environments and then contaminate food products, which is a major concern for food safety. The biofilm forming behavior of 143 L. monocytogenes strains was determined in four different media that were rich, moderate or poor in nutrients at 12°C, 20°C, 30°C and 37°C. The biofilm formation was mostly influenced by temperature, resulting in decreased biofilm formation with decreasing temperature. Biofilm formation was enhanced in nutrient-poor medium rather than in nutrient-rich medium, and especially in nutrient-poor medium significantly enhanced biofilm production was observed early in biofilm maturation underlining the effect of medium on biofilm formation rate. Also serotype had a significant effect on biofilm formation and was influenced by medium used because strains from both serotype 1/2b and 1/2a formed more biofilm than serotype 4b strains in nutrient-rich medium at 20°C, 30°C and 37°C, whereas in nutrient-poor medium the biofilm production levels of serotype 1/2a and 4b strains were rather similar and lower than serotype 1/2b strains. The strains used originated from various origins, including dairy, meat, industrial environment, human and animal, and the level of biofilm formation was not significantly affected by the origin of isolation, irrespective of medium used and temperature tested. A linear model was used to correlate crystal violet staining of biofilm production to the number of viable cells within the biofilm. This showed that crystal violet staining was poorly correlated to the number of viable cells in nutrient-poor medium, and LIVE/DEAD staining and DNase I treatment revealed that this could be attributed to the presence of non-viable cells and extracellular DNA in the biofilm matrix. The significant impact of intrinsic and extrinsic factors on biofilm production of L. monocytogenes underlined that niche-specific features determine the levels of biofilm produced, and insights in biofilm formation characteristics will allow us to further optimize strategies to control the biofilm formation of L. monocytogenes. [ABSTRACT FROM AUTHOR]

Fusarium verticillioides and Fusarium proliferatum are important phytopathogens which contaminate cereals in the Mediterranean climatic region with fumonisins. In this study we examined the interaction between the fungicide efficacy of tebuconazole and water potential (Ψw) (−0.7–7.0MPa)×temperature (20–35°C) on growth and FUM1 gene expression by real time RT-PCR (an indicator of fumonisin biosynthesis) in strains of both Fusarium species. Concentrations of tebuconazole required to reduce growth by 50 and 90% (ED50 and ED90 values) were determined. Growth of strains of both species was largely reduced by tebuconazole, with similar efficacy profiles in the interacting water potential×temperature conditions. In contrast, FUM1 expression was not generally reduced by tebuconazole. Moreover, sub-lethal doses in combination with mild water stress and temperatures less than 35°C significantly induced FUM1 expression with slight differences in both species. These results suggest that the efficacy of antifungal compounds to reduce mycotoxin risk would be more effective if consideration is given to both growth rate and toxin biosynthesis in relation to interacting environmental conditions. This is the first study linking fungicide efficacy of tebuconazole with environmental factor effects on control of growth and FUM1 gene expression of F. verticillioides and F. proliferatum. [ABSTRACT FROM AUTHOR]

Listeria monocytogenes is of particular concern in cold-smoked fish products as it can survive curing and cold-smoking, and can subsequently grow from low numbers to potentially hazardous levels during refrigerated storage. The purpose of this study was to (i) quantify the effects of organic acids, nisin, and their combinations on controlling L. monocytogenes growth on cold-smoked salmon at refrigeration temperatures, (ii) identify synergistic interactions of binary combinations of these antimicrobials, and (iii) determine if results from laboratory growth media can predict antimicrobial efficacy on cold-smoked salmon. Strains representing the genetic diversity of L. monocytogenes lineages I and II were grown in brain heart infusion (BHI) broth as well as on the surface of commercially produced wet-cured, cold-smoked salmon slices at 7°C. BHI broth and cold-smoked salmon were supplemented with sodium diacetate (SDA, 0.14% water phase (w.p.)), potassium lactate (PL, 2% w.p.), nisin (NI, 50ppm), and binary combinations of inhibitors at the same levels. Cell densities of L. monocytogenes were measured over time and used to calculate growth parameters, including initial cell density (N 0), lag phase (λ), maximum growth rate (μmax), and maximum cell density (N max) for each antimicrobial treatment. N 0 was significantly lowered by addition of NI with a similar average reduction on salmon (2.02±0.99 log(CFU/g)) and in BHI (1.51±0.83 log(CFU/ml)). Among all antimicrobial treatments, the combination of PL and SDA led to the greatest increase in λ both on salmon (7.1±3.6days) and in BHI (9.7±3.8days) when compared to the controls. The combination of PL and SDA had synergistic effects on increasing λ and lowering N max both in BHI and on salmon. Among all the treatments tested, the combination of NI and PL led to the greatest reductions in N max on salmon. We observed positive correlations between the growth parameters obtained from BHI broth and cold-smoked salmon, indicating that growth of L. monocytogenes in broth, to some extent, qualitatively reflected characteristics of growth on cold-smoked salmon under antimicrobial stresses. Results from BHI could quantitatively predict the variability of growth parameters obtained from salmon for lineage II strains, but not for lineage I strains. Although results from laboratory growth medium may not provide exact predictions of antimicrobial efficacy on cold-smoked salmon, they could be used to rapidly identify effective combinations for further examination on cold-smoked salmon. [ABSTRACT FROM AUTHOR]

Tahini is usually consumed without further heat treatment, and roasting of sesame seeds is the only Salmonella inactivation step in its traditional production process. This study examined the efficiency of the roasting process in the elimination of Salmonella from sesame seeds and the survival of Salmonella in tahini during storage. Sesame seed and tahini samples were inoculated with a cocktail of three serotypes of Salmonella (S. Typhimurium, S. Newport and S. Montevideo). Complete inactivation of Salmonella in sesame seeds, inoculated with 5.9log cfu/g, was achieved by roasting at 110°C for 60min, 130°C for 50min, or 150°C for 30min. Salmonella levels in tahini (aw =0.17) inoculated with 5.6log cfu/g and stored for 16weeks at 22 or 4°C decreased by 4.5 and 3.3 log, respectively. Results of this study demonstrated that the standard roasting process is sufficient to inactivate Salmonella in sesame seeds and low water activity of tahini prevents microbial growth, but its composition allows Salmonella to survive for at least 16weeks. Therefore, prevention of cross-contamination after roasting is crucial for food safety. [ABSTRACT FROM AUTHOR]

Abstract: During cheese ripening, micro-organisms grow as immobilised colonies, metabolising substrates present in the matrix which generate products triggered by enzymatic reactions. Local limitation rates of diffusion, either in the matrix or within the bacterial colonies, can be responsible for modulation in the metabolic and enzymatic activities of micro-organisms during ripening. How bacterial colonies immobilised in cheese are porous to these diffusing solutes has never been explored. The objective of this study was to determine if fluorescent dextrans of different sizes (4.4, 70 and 155kDa) are able to penetrate through colonies of Lactococcus lactis LD61 immobilised in solid media, either agar or model cheese. Confocal microscopic observations showed that lactococcus colonies immobilised in these two media were porous to dextrans from 4kDa to 155kDa. However, the rate of diffusion of the solutes was faster inside the colonies immobilised in ultrafiltered-cheese than in agar when large dextrans were considered (≥70kDa). The colonial shape of the lactococcus strain was also shown to be lenticular in agar and spherical in the model cheese, indicating that the physical pressure exerted on the colony by the surrounding casein network was probably isotropous in the UF-cheese but not in agar. In both cases, the fact that lactococcus colonies immobilised in solid media are porous to large dextran solutes suggests that substrates or enzymes are likely also to be able to migrate inside the colonies during cheese ripening. [Copyright &y& Elsevier]

Abstract: The long-term survival of enteric pathogens on butterhead lettuce seeds, and their subsequent survival and growth on seedlings were investigated. Lettuce seeds were inoculated at a high level with two Salmonella enterica and two Escherichia coli O157:H7 strains each (±8log10 CFU/g seed) and the survival of the pathogens was monitored over two years using standard plating techniques on selective medium. The Salmonella strains (serovars Typhimurium and Thompson) survived significantly better on the seeds than the E. coli O157:H7 strains (MB3885 and NCTC12900). When individual seeds were tested two years after inoculation, Salmonella was recovered from each individual seed, whereas E. coli O157:H7 only from 4% to 14% of the seeds, depending on the recovery method. When contaminated stored seeds were germinated and the seedlings examined for presence of the pathogens, it was clear that both pathogens were able to proliferate on the seedlings. Pathogen counts up to 5.92log10 CFU and 4.41log10 CFU per positive seedling were observed for Salmonella and E. coli O157:H7, respectively. Our study not only confirms the long-term survival of enteric pathogens on seeds but also shows that the pathogens maintain their ability to resuscitate and proliferate on the seedlings. Seeds or seedlings should be considered as contamination sources for the cultivation of leafy vegetables such as butterhead lettuce grown in greenhouses. [Copyright &y& Elsevier]

Abstract: This study aims to investigate the effects of supercritical carbon dioxide (SC-CO2) treatment on the inactivation of the natural microbial flora in cubed cooked ham. Response surface methodology with a central composite design was applied to determine the optimal process conditions and investigate the effect of three independent variables (pressure, temperature and treatment time). Additionally, analyses of texture, pH and color together with a storage study of the product were performed to determine its microbial and qualitative stability. Response surface analysis revealed that 12MPa, 50°C, 5min were the optimal conditions to obtain about 3.0, 1.6, and 2.5 Log(CFU/g) reductions of mesophilic aerobic bacteria, psychrophilic bacteria and lactic acid bacteria respectively. Inactivation to undetectable levels of yeasts and molds and coliforms was also obtained. A storage study of 30days at 4°C was carried out on the treated product (12MPa, 50°C, 5min) monitoring microbial growth, pH, texture, and color parameters (L*, a*, b* and ΔE). Microbial loads slightly increased and after 30days of storage reached the same levels detected in the fresh product. Color parameters (L⁎ , a⁎ , b⁎ ) showed slight variations while pH and texture did not change significantly. On the basis of the results obtained, SC-CO2 can be considered a promising technique to microbiologically stabilize cubed cooked ham and, in general, cut/sliced meat products without affecting its quality attributes. [Copyright &y& Elsevier]

Abstract: This study aimed to optimize the operating parameters of cold atmospheric plasma treatment to inhibit the growth of Aspergillus flavus on agar media and brown rice cereal bars. The effects of argon plasma jet treatment on the growth of A. flavus on malt extract agar (MEA) at powers of 20W and 40W with exposure times at 5, 15 and 25min were studied using response surface methodology (RSM) with a central composite face-centered (CCF) design. Multiple regression analysis indicated that plasma treatment at 40W for 25min is most effective for inhibiting growth of A. flavus on the agar medium. On brown rice cereal bars, plasma powered at 40W for 20min was capable of giving protection against A. flavus growth for up to 20days under storage conditions of 25°C and 100% RH. These results demonstrated the potential of cold atmospheric plasma jet treatment to control mold growth on various food products. [Copyright &y& Elsevier]

This study evaluated the effect of modified atmospheres (MAs) with different O2 concentrations on microbial growth and volatile metabolite production in gray shrimp (Crangon crangon) during storage at 4°C. Eight MAs were evaluated in total. Four of the MAs evaluated were without CO2: 0/0/100, 0/10/90, 0/30/70, 0/50/50 (% CO2/O2/N2) whilst the other four MAs all contained 50% CO2: 50/0/50, 50/10/40, 50/30/20, 50/50/0 (% CO2/O2/N2). Volatile spoilage metabolites were identified by thermal desorption GC-MS and quantified during storage by selective ion flow tube mass spectrometry (SIFT-MS). In comparison to microbial growth observed with an atmosphere of 100% N2, microbial growth was stimulated by the addition of O2 in the MAP in the absence of CO2. Under these conditions the total psychrotrophic counts exceeded 7 log cfug−1 after just 3days of storage. However, in the presence of 50% CO2 the total psychrotrophic count exceeded 7 log cfug−1 after 5days of storage. The combination of 50% CO2 and 50% O2 significantly inhibited microbial growth. For this MA condition, a diminishing effect on the production of metabolites was also observed, especially for amines and sulfur compounds, which constituted the major fraction of components causing the offensive odor. [Copyright &y& Elsevier]