Frank Devlieghere

Ghent University, Gand, Flanders, Belgium

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Publications (237)462.67 Total impact

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    ABSTRACT: The aim of this study was to investigate the response of Campylobacter jejuni at single-cell level when exposed to different concentrations of chlorine dioxide (ClO(2)). The parameter of choice, intracellular pH (pH(i)), was determined by using fluorescence ratio imaging microscopy with a pH-sensitive, ratiometric 5(6)-carboxyfluorescein diacetate succinimidyl ester probe. In addition, the culturability expressed in colony counts was determined. Our results revealed that several subpopulations with different physiological states, as judged by their pH(i), were created by ClO(2) treatment. The greater the concentration of ClO(2), the smaller the subpopulation of healthy cells with pH(i) > 6.8 and the smaller the colony count as determined on nonselective agar plates. ClO(2) at concentrations (60 ppm) induced injuries that resulted in complete loss of culturability and adversely affected the ability to resuscitate under subsequent more favorable conditions. The presence of injured cells in food could present a risk for public health. Additional hurdles have to be included in food preservation to suppress the survival and recovery of injured cells.
    Foodborne Pathogens and Disease 10/2010; 8(2):325-8. · 2.28 Impact Factor
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    ABSTRACT: The growth inhibiting effects of NaCl and selected simple salt replacers (CaCl(2), MgCl(2), KCl and MgSO(4)) on the growth of Lactobacillus sakei were studied in de Man Rogosa Sharpe broth at 7 degrees C over a water phase concentration of 0 to 6.4%. The divalent chloride salts (CaCl(2) in particular) generally had the largest antimicrobial activities at equivalent water phase concentrations, molalities or water activity (a(w)) values. MgSO(4) had not only the least antimicrobial activity but also the smallest a(w) depressing capacity. The results also showed that the antimicrobial effects of CaCl(2) were not fully accounted for by its a(w) depressing effects. Challenge tests performed on cooked ham and white sauce showed that reduction of NaCl levels by 28 and 33%, respectively, had no influence on the microbial stability of these products to L. sakei. Ultimately the study concluded that the microbiological consequences of the full or partial replacement of NaCl on the growth of L. sakei largely depend on the initial level of NaCl, the level of replacement and the nature of the salt replacer used. Altered stability to L. sakei is most likely given a high initial NaCl level, combined with a large level of partial replacement with either CaCl(2) (increased stability) or MgSO(4) (reduced stability) as the replacer.
    International journal of food microbiology 09/2010; 143(1-2):9-16. · 3.01 Impact Factor
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    ABSTRACT: The effect of NaCl and various NaCl replacers (CaCl(2), MgCl(2), KCl and MgSO(4)) on the growth of Penicillium roqueforti and Aspergillus niger was evaluated at 22 degrees C. In addition, challenge tests were performed on white bread to determine the consequences of NaCl reduction with or without partial replacement on the growth of P. roqueforti. From the results obtained it can be concluded that at equivalent water phase concentrations the isolates exhibited differing sensitivities to the salts evaluated with NaCl and MgCl(2) having the greatest inhibitory action on the growth of A. niger and P. roqueforti, respectively. MgSO(4) had the least antifungal activity. At equivalent molalities, CaCl(2) had in general the largest antifungal activity. Although the water activity (a(w)) lowering effects of the compounds studied play a large role in explaining the trends observed, at equivalent water phase concentrations MgCl(2) was found to have a smaller inhibitory effect on A. niger than that expected from its a(w) depressing effect. The challenge tests revealed that no difference occurred in the growth of P. roqueforti on standard white bread, bread with 30% less NaCl and bread in which 30% of the NaCl has been partially replaced by a mixture of KCl and Sub4Salt. These results are of importance in assessing the possible microbiological consequences of NaCl reduction or replacement in bread and similar bakery products.
    Food Microbiology 09/2010; 27(6):749-56. · 3.41 Impact Factor
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    ABSTRACT: There is a need to measure the food safety performance in the agri-food chain without performing actual microbiological analysis. A food safety performance diagnosis, based on seven indicators and corresponding assessment grids have been developed and validated in nine European food businesses. Validation was conducted on the basis of an extensive microbiological assessment scheme (MAS). The assumption behind the food safety performance diagnosis is that food businesses which evaluate the performance of their food safety management system in a more structured way and according to very strict and specific criteria will have a better insight in their actual microbiological food safety performance, because food safety problems will be more systematically detected. The diagnosis can be a useful tool to have a first indication about the microbiological performance of a food safety management system present in a food business. Moreover, the diagnosis can be used in quantitative studies to get insight in the effect of interventions on sector or governmental level.
    International journal of food microbiology 07/2010; 141 Suppl 1:S180-7. · 3.01 Impact Factor
  • Andreja Rajkovic, Nada Smigic, Frank Devlieghere
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    ABSTRACT: The objective of this review has been to disclose collected information on benefits and risks of selected "less-than - sterilizing" processes applied to control microbial hazards in food that was meticulously collected and critically reviewed during five years of EU Sixth framework project "Pathogen Combat". The target organisms of the project, and thus of this review, too, were Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni. Due to their specific response and high relevancy to the food safety, foodborne viruses and spores, were also discussed within the scope of this review. Selected treatments comprised High Pressure Processing, Intense Light Pulses, treatments with organic acids, treatments with chlorine dioxide and for their relevancy also mild heat treatments and Pulsed Electric Field processing were included. The main aspects included in this review were principles of the processes used and their application, sub-lethal injury and its consequences on microbial food safety, and legal platform and its impact on wide use of the treatments. Finally a reflection has been made to combined application of different hurdles and accompanying risks.
    International journal of food microbiology 07/2010; 141 Suppl 1:S29-42. · 3.01 Impact Factor
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    ABSTRACT: Quantitative risk assessment studies performed elsewhere showed the importance of reducing counts of Campylobacter jejuni on chicken carcasses for decrease of incidence of human campylobacteriosis. The current study indicated that 1.8 log CFU/g reduction of inoculated C. jejuni (6 log CFU/g) can be achieved by decontamination with lactic acid buffered with sodium lacatate (LA/NaLA, 10% w/v, pH 3.0). Subsequent packaging under modified atmosphere of 80% O(2)/20%N(2) resulted in additional reduction of approximately 1.2 log CFU/g. These results were confirmed in naturally contaminated samples (2-3 log CFU/g) resulting in immediate reduction of present C. jejuni under the limit of enumeration (1 log CFU/g). However, enrichment showed presence of C. jejuni in 10g of sample. Under 80% O(2) LA/NaLA treated C. jejuni remained detectable per 10g until day 7, after which no positive samples were found until the end of the two-weeks storage. Under 80% CO(2) LA/NaLA treated C. jejuni remained fluctuating at 10 CFU/g until the end of two-weeks storage. Control cells were reduced by approx. 1.5 log CFU/g during storage under 80% O(2)/20% N(2), whereas no reduction was observed under 80% CO(2)/20% N(2). The present study showed the potential of buffered lactic acid and high-O(2) MAP to reduce C. jejuni both on inoculated and naturally contaminated samples. The immediate effect of decontamination was further extended by additive, not synergistic, effect of 80% O(2), suggesting the practical value of the tested concept in combating C. jejuni on chicken carcasses.
    International journal of food microbiology 06/2010; 140(2-3):201-6. · 3.01 Impact Factor
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    ABSTRACT: The objective of this study was to investigate whether bacterial cells could develop resistance (as a part of their adaptation strategy) to high-pressure CO(2) (HPCD) inactivation. Alternating cycles of exposure to pressurized CO(2) (10.5 MPa, 35 degrees C, 400 min(-1), 70% working volume ratio during 10 min) and re-growth of the surviving subpopulation were used to investigate possible increases in the resistance of Escherichia coli and Listeria monocytogenes to HPCD. The results show an increased resistance of both pathogens tested after seven cycles of inactivation. Increase in the resistance after 15 cycles resulted in a difference of 2.4 log CFU ml(-1) in log N(0)/N(i) when parental (N(0)) and treated cultures (N(i)) of E. coli and L. monocytogenes were compared. Current findings indicate the ability of micro-organisms to adapt to HPCD preservation technology. The occurrence of HPCD-resistant micro-organisms could pose a new hazard to the safety and stability of HPCD-processed foods.
    Letters in Applied Microbiology 06/2010; 50(6):653-6. · 1.63 Impact Factor
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    ABSTRACT: In this study, the relationship between (irreversible) membrane permeabilization and loss of viability in Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae cells subjected to high pressure carbon dioxide (HPCD) treatment at different process conditions including temperature (35-45 degrees C), pressure (10.5-21.0 MPa) and treatment time (0-60 min) was examined. Loss of membrane integrity was measured as increased uptake of the fluorescent dye propidium iodide (PI) with spectrofluorometry, while cell inactivation was determined by viable cell count. Uptake of PI by all three strains indicated that membrane damage is involved in the mechanism of HPCD inactivation of vegetative cells. The extent of membrane permeabilization and cellular death increased with the severity of the HPCD treatment. The resistance of the three tested organisms to HPCD treatment changed as a function of treatment time, leading to significant tailing in the survival curves, and was dependent on pressure and temperature. The results in this study also indicated a HPCD-induced damage on nucleic acids during cell inactivation. Transmission electron microscopy showed that HPCD treatment had a profound effect on the intracellular organization of the micro-organisms and influenced the permeability of the bacterial cells by introducing pores in the cell wall.
    Food Microbiology 06/2010; 27(4):541-9. · 3.41 Impact Factor
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    ABSTRACT: Several studies have shown that food structure causes slower growth rates and narrower growth boundaries of bacteria compared to laboratory media. In predictive microbiology, both a(w) or corresponding solute concentration (mainly NaCl) have been used as a growth influencing factor for kinetic models or growth/no growth interface models. The majority of these models have been based on data generated in liquid broth media with NaCl as the predominant a(w) influencing solute. However, in complex food systems, other a(w) influencing components might be present, next to NaCl. In this study, the growth rate of Salmonella typhimurium was studied in the growth region and the growth/no growth response was tested in Tryptic Soy Broth at 20 degrees C at varying gelatin concentration (0, 10, 50 g L(-1) gelatin), pH (3.25-5.5) and water activity (a(w)) (0.929-0.996). From the viewpoint of water activity, the results suggest that NaCl is the main a(w) affecting compound. However, gelatin seemed to have an effect on medium a(w) too. Moreover, there is also an interaction effect between NaCl and gelatin. From the microbial viewpoint, the results confirmed that the a(w) decreasing effect of gelatin is less harmful to cells than the effect of Na(+) ions. The unexpected shift of the growth/no growth interface to more severe conditions when going from a liquid medium to a medium with 10 g L(-1) gelatin is more pronounced when formulating the models in terms of a(w) than in terms of NaCl concentrations. At 50 g L(-1) gelatin, the model factored with NaCl concentration shifts to milder conditions (concordant to literature results) while the model with a(w) indicates a further shift to more severe conditions, which is due to the water activity lowering effect of gelatin and the interaction between gelatin and NaCl. The results suggest that solute concentration should be used instead of a(w), both for kinetic models in the growth region and for growth/no growth interface models, if the transferability of models to solid foods is to be increased.
    Food Microbiology 04/2010; 27(2):220-8. · 3.41 Impact Factor
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    ABSTRACT: Selective ion flow tube mass spectrometry (SIFT-MS) is a direct mass spectrometric technique that allows qualitative and quantitative analysis of a large number of volatile organic compounds. Because of its speed and ease of use, this nondestructive technique could be considered as a practical tool for quality control. This research focuses on the possibilities of direct headspace sampling by SIFT-MS for the quantification of the volatile basic nitrogen content (TVB-N) of fish fillets. These volatile bases [trimethylamine (TMA), dimethylamine (DMA), and ammonia] give additional information in conjunction with the sensory scoring and microbiological analysis about the quality of the fish fillets. This research validates in a first part the SIFT-MS method for the quantification of the volatile bases in mixed cod samples. With regard to the investigated linearity, repeatability, reproducibility, recovery, limit of detection, and limit of quantification, SIFT-MS appeared to be an adequate technique for measuring volatile bases spiked on cod. In the second part of this research, the technique was validated for the analysis of volatile bases on cod fillets during a storage experiment under ice. A good correlation was obtained between the proposed direct headspace sampling and traditional methods. The sensitivity of the SIFT-MS method can be improved when cod fillets are made more alkaline (pH >11) during sampling.
    Journal of Agricultural and Food Chemistry 04/2010; 58(9):5213-9. · 2.91 Impact Factor
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    ABSTRACT: As mild decontamination treatments are gaining more and more interest due to increased consumer demands for fresh foods, it is of great importance to establish the influence of decontamination treatments on the subsequent bacterial behaviour under suboptimal storage conditions. For this purpose Campylobacter jejuni cells treated with lactic acid (LA, 3% lactic acid, pH 4.0, 2 min) or chlorine dioxide (ClO(2), 20 ppm, 2 min) were inoculated in Bolton broth (pH 6.0) and incubated under 80% O(2)/20% N(2), 80% CO(2)/20% N(2), air or micro-aerophilic (10% CO(2)/85% N(2)/5% O(2)) atmosphere, at 4 degrees C during 7 days. Treatment with water served as a control. The most suppressive atmosphere for the survival of C. jejuni was O(2)-rich atmosphere, followed by air, micro-aerophilic and CO(2)-rich atmosphere. The survival of C. jejuni was dependent on the type of initial decontamination treatment, with water treated cells showing the greatest survival followed by LA and ClO(2) treated cells. Intracellular pH (pH(i)) of individual C. jejuni cells was determined using Fluorescence Ratio Imaging Microscopy (FRIM). At all tested conditions, different subpopulation of the cells could be distinguished based on their pH(i) values. The pH(i) response was independent on the surrounding atmosphere since similar distribution of the subpopulations was observed for all tested atmospheres. However, the pH(i) response was dependent on the initial decontamination treatment. The investigation of intracellular parameters gave an insight into pathogen behaviour under stressful conditions at intracellular level. The results obtained in this study highlighted the importance of combining decontamination technologies with subsequent preservation techniques to the control survival and growth of foodborne pathogens.
    International journal of food microbiology 01/2010; 141 Suppl 1:S140-6. · 3.01 Impact Factor
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    ABSTRACT: The relationship between water activity (aw) and concentration of NaCl, sucrose and various simple and commercial salt, sugar and fat replacers was determined. The model originally developed by Favetto and Chirife (1985) and extended by Roa and Tapia (1998) was successfully used to model the relationship between aw and molality of the binary and multi-component aqueous solutions. These models were then reparameterized to enable the aw to be modeled as function of the water phase concentrations of binary and multi-component solutions. This reparameterization enables the modeling of the aw depressing effects of compounds for which sufficient data required to calculate the molecular weight cannot be obtained. Both models were successfully used to predict the aw of some food products including meat and fish products and mayonnaises with average deviations of 0.0052 from the measured aw, and bias and accuracy factors of 0.995 and 1.0057, respectively.
    Journal of Food Engineering. 01/2010; 96(3):433-439.
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    ABSTRACT: Changes in food supply chains, health and demographic situations, lifestyle and social situations, environmental conditions, and increased legislative requirements have led to significant efforts in the development of quality and safety management systems in agribusiness and food industry worldwide (Ropkins and Beck, 2000; Efstratiadis, Karirti, and Arvanitoyannis, 2000; Jacxsens, et al, 2009a, Luning and Marcelis, 2009a). Nowadays, companies have implemented various quality assurance (QA) guidelines and standards, such as GMP and HACCP guidelines (like General Principles of food hygiene (Codex Alimentarius 2003), GFSI guidance document (GFSI (2007), and quality assurance standards (like ISO 9001:2008 (2008), ISO22000:2005 (2005), BRC (2008), and IFS (2007) into their company own food safety management system. The performance of such systems in practice is, however, still variable. Moreover, the continuous pressure on food safety management system (FSMS) performance and the dynamic environment wherein the systems operate (such as emerging pathogens, changing consumer demands, developments in preservation techniques) require that they can be systematically analysed to determine opportunities for improvement (Wallace, et al, 2005; Manning et al, 2006; Van der Spiegel et al, 2006; Cornier et al, 2007; Luning et al, 2009a). Within the European project entitled ‘PathogenCombat- EU FOOD-CT-2005-007081’ various tools have been developed to support food companies and establishments in systematically analysing and judging their food safety management system and its microbiological performance as basis for strategic choices on interventions to improve the FSMS performance. This chapter describes briefly principles of the major tools that have been developed and some others, which are still under still under construction.
    01/2010: pages 31-43; , ISBN: 9788478670543
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    ABSTRACT: The current quality assurance and control tools and methods to prevent and/or to control microbiological risks associated with fresh produce are challenged due to the following pressures upon the food supply chain, i.e. changing consumption patterns, globalization and climate change. It demonstrates the need for scientific research and development of new and/or improved tools, techniques and practices to adapt the current risk management systems. In this paper, a conceptual research approach is presented to analyse the complexity of the climate change and globalization challenge on the fresh produce supply chain taken as a case study. The factors which affect the vulnerability of the fresh produce chain demand a multidisciplinary research approach. The proposed knowledge-based modelling system is believed to be a most appropriate way to identify problems and to offer solutions to monitor and prevent microbiological food safety risks during all phases of food production and supply. To explore the potential impact of climate change and globalization, baseline information can be obtained by surveillance and performance measurement of implemented food safety management systems. Simulation of climate change scenarios and the logistic chain of fresh produce, along with mathematical models to optimize packaging technology to maintain quality and safety of fresh produce are tools to provide insights in the complex dynamic ecosystem. They are the basis for elaboration of risk assessment studies to scientifically support management options and decisions to new microbiological threats related to globalization and climate change in the fresh produce supply chain. This research concept as such will contribute to develop strategies in order to guarantee the (microbiological) food safety of fresh produce on the long term
    Food Research International 43 (2010) 7. 01/2010;
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    ABSTRACT: The main objective of this work was to explore the applicability of the Intense Light Pulses (ILP) for decontamination of a stainless steel meat contact surface, exemplified by a slicing knife, as a function of time between contamination and decontamination, number of light pulses applied, and the prior contact with different meat matrices. Listeria monocytogenes and Escherichia coli O157:H7 were chosen as the challenge microorganisms. The ILP system was a laboratory-scale four-lamp batch system generating 3 J/cm2 with an input voltage of 3000 V. The results obtained demonstrate successful application of ILP treatment for reduction of L. monocytogenes and E. coli O157:H7 on a surface of stainless steel slicing knife. The inactivation effectiveness depended on the type of meat product that was in the contact with the treated surface and on the time between the contamination and the ILP treatment. Statistical analysis showed the significant interaction between the time and type of meat product on the effectiveness of ILP treatment. The highest effectiveness of the ILP (the complete inactivation of 6.5 log CFU/side of knife) was obtained when the knife surface was in contact with the products containing lower fat and protein content and when it was treated with pulsed light as fast as possible after the contamination (within 60 s). The decontamination efficacy of ILP treatment could not be improved by multiple light pulses if lost due to the extended time between the moment of contamination and ILP treatment. Results showed that the suggested approach can be very effective as an intervention strategy along meat processing lines preventing cross-contamination between the equipment and the final product.
    Journal of Food Engineering. 01/2010;
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    ABSTRACT: The shelf life of a food product is largely determined by its chemical and microbiological stability. In this respect, the gas composition surrounding a packaged product plays a major role. Modified Atmosphere Packaging (MAP) is a packaging technique that usually reduces the headspace oxygen to a preferable minimum for most food products. Besides the residual oxygen, the O2-permeability of the packaging material is also important, as it determines the amount of oxygen permeating into the package during storage. This paper describes the development of a practical software simulation tool to predict the amount of oxygen permeating into the headspace during storage for a variety of multilayer packaging configurations. The simulation tool gives access to simulation models for mono- and multilayer films, trays covered with top foils and bottles with caps. The user can compose his/her own (multilayer) packaging material and check the oxygen ingress over time for different temperature conditions for all packaging configurations.Industrial relevanceThe software simulation tool is of industrial relevance to food companies, as they can use it to select or compare different films, but also to underpin their choice for a certain packaging material with regard to the sensitivity of the food product to oxygen and the desirable shelf life. The simulation program also provides food companies with information about the influence of storage conditions, like time and temperature, on the ingress of oxygen in their food package throughout the storage-distribution chain. On the other hand, it can also be used by packaging suppliers to predict the oxygen permeability in the optimization process of new films and as a client support tool.
    Innovative Food Science & Emerging Technologies 01/2010; 11(3):511-519. · 2.53 Impact Factor
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    ABSTRACT: High-pressure carbon dioxide (HPCD) treatment is currently considered as an attractive non-thermal process for preserving food. Since the first level of interaction between HPCD and the bacterial cells is lowering of the pH, knowledge of the pH of a food product in contact with CO2 at high-pressure conditions is essential for a better understanding of the inactivation mechanism of HPCD. Therefore, a mathematical model was developed to predict the pH in complex aqueous food systems in contact with CO2 at high-pressure conditions as function of pressure, temperature and buffer capacity. In addition, a spectrofluorometric method using calcein as fluorescent pH indicator was designed for the in situ measurement of the pH of complex aqueous systems in contact with pressurized CO2 as function of pressure (10.5–18.0MPa), temperature (25–35°C), initial pH (4.0–8.0), working volume ratio (41.6–70.0%) and broth composition (0.1M citrate buffer, 0.1M phosphate buffer and 10% whey protein). To mimic a complex matrix, the bacterial Brain Heart Infusion (BHI) broth was used.In general, there was a good agreement between the measured and predicted pH values. Only for the lowest initial pH of the broth, a discrepancy between the measured and calculated pH values was noticed, implying that the proposed model needs some further refinement to properly take into account non-ideality of the liquid phase. Furthermore, the pH of the broth was significantly influenced by the initial pH of the solution but was not dependent on pressure, temperature and working volume ratio. The addition of complementary buffers to the broth also influenced the pH drop and this effect was dependent on the initial pH of the solution.
    Journal of Supercritical Fluids - J SUPERCRIT FLUID. 01/2010; 55(1):77-85.
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    ABSTRACT: While maintaining nutritional and sensorial attributes of fresh foods mild processing technologies generally deliver microbiologically perishable food products. Currently little information exists on possible increase in the resistance of pathogens after repetitive exposure to mild (sub-lethal) treatments. Multiple strain-cocktails of Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni were exposed to 20 consecutive cycles of sub-lethal inactivation by three different techniques. Used techniques comprised inactivation with lactic acid (LA), chlorine dioxide (ClO(2)) and intense light pulses (ILP). Results showed that the selection of resistant cells was both species and technique dependent. While repetitive cycles of ClO(2) treatment did not result in increased resistance, repetitive inactivation with LA yielded L. monocytogenes culture of higher resistance in comparison to the parental culture. The increased resistance, expressed as decreased level of reduction in bacterial counts in subsequent inactivation cycles, was also observed with ILP for both L. monocytogenes and E. coli O157:H7 strains. Visual trend observations were confirmed through statistical linear regression analysis. No such effects were noted for C. jejuni which became undetectable after first 2-5 cycles. Current findings indicate the ability of foodborne pathogens to adapt to mild bactericidal treatments creating new challenges in risk assessment and more specifically in hazard analysis.
    Food Microbiology 12/2009; 26(8):889-95. · 3.41 Impact Factor
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    ABSTRACT: Since several disadvantages are associated with the use of sodium hypochlorite as a decontamination agent, the attention for alternative agents such as peroxyacetic acid (PAA) is increasing. In this study the effectiveness of PAA to remove the native microflora was tested in four types of fresh-cut vegetables: grated carrots, fresh-cut white cabbage, iceberg lettuce and leek. Furthermore, the influence of varying PAA concentrations (0, 25, 80, 150 and 250 ppm) and varying contact times (1, 5 and 10 min) was described by means of a linear model. The efficiency of PAA to remove the native flora was highly dependent on the type of fresh-cut produce: the highest microbial reductions were obtained for carrots (0.5-3.5 log cfu/g) and white cabbage (0.5-3.5 log cfu/g) followed by iceberg lettuce (0.4-2.4 log cfu/g). The obtained efficiency was the lowest for fresh-cut leek (0.4-1.4 log cfu/g). Furthermore, all the treated samples, regardless of the type of vegetable and the contact time and concentration of the PAA treatment, were acceptable for consumption.
    Food Microbiology 12/2009; 26(8):882-8. · 3.41 Impact Factor
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    ABSTRACT: The aim of the study was to develop mathematical models describing growth/no growth (G/NG) boundaries of the highly resistant food spoilage yeast-Zygosaccharomyces bailii-in different environmental conditions, taking acidified sauces as the target product. By applying these models, the stability of products with characteristics within the investigated pH, a(w) and acetic acid ranges can be evaluated. Besides, the well-defined no growth regions can be used in the development of guidelines regarding formulation of new shelf-stable foods without using chemical preservatives, which would facilitate the innovation of additive-free products. Experiments were performed at different temperatures and periods (22 degrees C for 45 and 60days, 30 degrees C for 45days) in 150 modified Sabouraud media characterized by high amount of sugars (glucose and fructose, 15% (w/v)), acetic acid (0.0-2.5% (v/v), 6 levels), pH (3.0-5.0, 5 levels) and a(w) (0.93-0.97, 5 levels). These time and temperature combinations were chosen as they are commonly applied for shelf-stable foods. The media were inoculated with ca. 4.5 log CFU/ml and yeast growth was monitored daily using optical density measurements. Every condition was examined in 20 replicates in order to yield accurate growth probabilities. Three separate ordinary logistic regression models were developed for different tested temperatures and incubation time. The total acetic acid concentration was considered as variable for all models. In general, when one intrinsic inhibitory factor became more stringent, the G/NG boundary shifted to less stressful conditions of the other two factors, resulting in enlarged no growth zones. Abrupt changes of growth probability often occurred around the transition zones (between growth and no growth regions), which indicates that minor variations in environmental conditions near the G/NG boundaries can cause a significant impact on the growth probability. When comparing growth after 45days between the two tested temperatures, an unexpected phenomenon was observed: the no growth region at 30 degrees C was larger than the one at 22 degrees C, though it is known that 30 degrees C is the optimal growth temperature for Z. bailii. These results show that lowering temperature does not always lead to a reduced growth of the yeast (i.e. more stable foods) and storing shelf-stable products at the higher temperature (30 degrees C) is not always the worst case. In addition, at 22 degrees C, there was no significant difference in no growth zones between the two incubation periods (45 and 60days), implying that the no growth zones remain unchanged if the experimental time is sufficiently long.
    International journal of food microbiology 10/2009; 137(1):1-12. · 3.01 Impact Factor

Publication Stats

3k Citations
462.67 Total Impact Points


  • 1997–2014
    • Ghent University
      • • Department of Food Safety and Food Quality
      • • Faculty of Bioscience Engineering
      Gand, Flanders, Belgium
  • 2013
    • Can Tho University
      • Department of Food Technology
      Kan Tho, Cần Thơ, Vietnam
    • University of Belgrade
      • Faculty of Agriculture
      Beograd, Central Serbia, Serbia
  • 2009–2011
    • Institute for Agricultural and Fisheries Research
      • Technology and Food Science Unit
      Meirelbeke, Flanders, Belgium
  • 2001–2011
    • KU Leuven
      • Department of Chemical Engineering
      Leuven, VLG, Belgium
  • 2007–2010
    • Flemish Institute for Technological Research
      Moll, Flanders, Belgium
    • Gulu University (GU)
      Гул, Northern Region, Uganda
  • 2003
    • Sokoine University of Agriculture (SUA)
      Murogoro, Morogoro Region, Tanzania