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Biomedical subjects

G J Nychas

Publications and source records attributed to G J Nychas.

At least 19 recordsLinked to original sources
PubMed2001

Survival of Escherichia coli O157:H7 during the fermentation of Spanish-style green table olives (conservolea variety) supplemented with different carbon sources.

Olives were supplemented with two different carbon sources (sucrose and glucose) at five different levels (0%, 0.1%, 0.3%, 0.5% and 1%) and the fermentation procedure was followed after inoculation with or without starter culture. Inhibition of Escherichia coli O157:H7 was evident in all fermentation procedures regardless of the treatment used. The pathogen numbers declined but did not die out during fermentation. It was evident that the rate of death was higher in samples supplemented with starter cultures compared to natural fermentation. The production of acids during fermentation seems to be the main factor that governs the behaviour of this pathogen under such stress conditions. The HPLC analysis revealed that lactate, formate and acetate were among the end-products during the fermentation of green olives.

Acetates↗
PubMed2001

Performance of Pseudomonas CFC-selective medium in the fish storage ecosystems.

Pseudomonas agar base supplemented with cephaloridine, fucidin, and cetrimide (CFC) was used to count Pseudomonas populations on fish. Both Enterobacteriaceae and Shewanella putrefaciens were able to grow on the CFC medium. Evaluation of the performance of CFC-selective for pseudomonads medium, on fish samples stored aerobically and under a modified atmosphere at 0, 10 and 20 degrees C was tested. The selectivity of the medium was affected by storage temperatures and the type of packaging of the fish samples. The selectivity of the medium diminished as the population increased and for samples stored at high temperature (20 degrees C) or under modified atmospheres. When designing adequate selectivity of a medium, interfering organisms should be taken into account, especially when the background flora tends to be more robust than the organisms to be counted or detected.

Animals↗
PubMed2001

Ecophysiological attributes of a Lactobacillus sp. and a Pseudomonas sp. on sterile beef fillets in relation to storage temperature and film permeability.

AIMS: To determine the combined effect of packaging film and temperature on the rate and type of end-products caused by the growth of two main contrasting prevailing organisms in air and 100% CO2, Pseudomonas sp. and Lactobacillus sp., respectively. METHODS AND RESULTS: Pseudomonas sp. and Lactobacillus sp. were inoculated individually on sterile meat fillets. The samples were packed in air or 100% CO2, using a high and a low permeable film, and stored at 0 and 10 degrees C. Pseudomonas sp. grew aerobically and in 100% CO2 using high permeable film at both storage temperatures, while film permeability significantly affected the growth of Lactobacillus sp. only at 10 degrees C. Enzymatic kits and HPLC and GC analysis were used to determine the chemical changes of the samples throughout storage. Pseudomonas sp. presented a greater rate of consumption of glucose and lactate than Lactobacillus sp. in samples stored aerobically or with high permeable film. Propanol-1 and two unidentified organic acids were present only in samples inoculated with Pseudomonas sp., while acetaldehyde, ethanol, diacetyl and acetoin were detected in samples inoculated with Lactobacillus sp. CONCLUSION: Since different microbial species and introduction of new packaging methods affect spoilage reactions of meat either qualitatively or quantitatively, a combination of several chemical indicators should be thoroughly investigated. SIGNIFICANCE AND IMPACT OF THE STUDY: The present study provides information on how and when such potential indicators can be exploited for the benefit of the industry and consumer.

Acetaldehyde↗
PubMed2001

A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol.

AIMS: The minimum inhibitory concentration (MIC) of oregano essential oil (OEO) and two of its principle components, i.e. thymol and carvacrol, against Pseudomonas aeruginosa and Staphylococcus aureus was assessed by using an innovative technique. The mechanism of action of the above substances was also investigated. METHODS AND RESULTS: The applied technique uses 100-well microtitre plate and collects turbidimetric growth data. To produce the inhibition profiles, a wide range of concentrations were tested for each of the three compounds, as well as for carvacrol-thymol mixtures. Following a specific mathematical analysis of the observed inhibition profiles from all compounds, it was suggested that mixtures of carvacrol and thymol gave an additive effect and that the overall inhibition by OEO can be attributed mainly to the additive antimicrobial action of these two compounds. Addition of low amounts of each additive: (a) increased permeability of cells to the nuclear stain EB, (b) dissipated pH gradients as indicated by the CFDA-SE fluorescent probe irrespective of glucose availability and (c) caused leakage of inorganic ions. CONCLUSION: Mixing carvacrol and thymol at proper amounts may exert the total inhibition that is evident by oregano essential oil. Such inhibition is due to damage in membrane integrity, which further affects pH homeostasis and equilibrium of inorganic ions. SIGNIFICANCE AND IMPACT OF THE STUDY: The knowledge of extent and mode of inhibition of specific compounds, which are present in plant extracts, may contribute to the successful application of such natural preservatives in foods, since certain combinations of carvacrol-thymol provide as high inhibition as oregano essential oil with a smaller flavour impact.

Cell Membrane↗
PubMed2001

Effect of oregano essential oil on microbiological and physico-chemical attributes of minced meat stored in air and modified atmospheres.

AIMS: This study aimed to determine the combined effect of packaging (air, modified atmosphere) with or without the addition of essential oil not only on the selection of microbial association of meat but also to determine any significant difference in microbial metabolites produced from the prevailing bacteria. METHODS AND RESULTS: Samples of minced meat were mixed with different concentration of oregano essential oil (0, 0.05, 0.5 and 1% v/w) and packed under aerobic or with modified atmosphere (Mixed Gas Modified Atmosphere--MGMA, 40% CO2/30% N2/30% O2; or CO2 Modified Atmosphere--COMA, 100% CO2) and stored at 5 degrees C. In all packaging conditions, only concentrations of 0.5% and 1% oregano oil were effective. Inhibition was evident in the order air < MGMA < COMA. Oregano essential oil delayed glucose and lactate consumption aerobically as well as under MGMA. pH changes were also evident. Furthermore, proteolysis was significantly inhibited in aerobically stored samples, and so was the production of acetate under MAP. Similar results were obtained for the other organic acids eluted from HPLC column. CONCLUSIONS: Oregano essential oil delayed microbial growth and suppressed the final counts of the spoilage micro-organisms. It also caused a pronounced alteration in the physico-chemical properties of the minced meat. SIGNIFICANCE AND IMPACT OF THE STUDY: Microbial analysis alone as spoilage index may misrepresent the effect of a hurdle such as essential oils on spoilage.

Aerobiosis↗
PubMed2001

Development and assessment of an intelligent shelf life decision system for quality optimization of the food chill chain.

The principles of application of a Shelf Life Decision System (SLDS) for the optimization of the distribution of chilled fresh and minimally processed food products are developed. The SLDS integrates predictive kinetic models of food spoilage, data on initial quality from rapid techniques, and the capacity to continuously monitor temperature history of the food product with Time Temperature Integrators (TTIs) into an effective chill chain management tool that leads to an improved narrow distribution of quality at consumption time, effectively reducing the probability of products consumed past shelf life end. The applicability and effectiveness of the SLDS is demonstrated and evaluated based on actual food spoilage and TTI kinetics and chill chain data employing the Monte Carlo simulation method.

Animals↗
PubMed2000

Application of a systematic experimental procedure to develop a microbial model for rapid fish shelf life predictions.

A systematic experimental procedure for fish shelf-life modelling was used to develop a model for predicting the quality of fish in the chill chain. For this, the growth of the naturally occurring bacteria pseudomonads, Shewanella putrefaciens, Enterobacteriaceae, lactic acid bacteria and yeasts, on gilt-head seabream (Sparus aurata), was studied at temperatures from 0 to 15 degrees C. The results from the microbiological, organoleptical and chemical analysis conducted on naturally contaminated fish as well as on inoculated sterile fish blocks identified pseudomonads as a good spoilage index. Growth of pseudomonads was modelled as a function of storage temperature and correlated to organoleptical shelf life. To reduce the time required for the enumeration of the initial pseudomonads number, which is crucial information for shelf life prediction, a conductance assay was established. Compared with the conventional microbiological tests, this method gave results in one-fourth of the time.

Animals↗
PubMed2000

Behaviour of Listeria monocytogenes and autochthonous flora on meat stored under aerobic, vacuum and modified atmosphere packaging conditions with or without the presence of oregano essential oil at 5 degrees C.

The effect of aerobic, modified atmosphere packaging (MAP; 40% CO2/30% O2/30% N2) and vacuum packaging (VP) on the growth/survival of Listeria monocytogenes on sterile and naturally contaminated beef meat fillets was studied in relation to film permeability and oregano essential oil. The dominant micro-organism(s) and the effect of the endogenous flora on the growth/survival of L. monocytogenes were dependent on the type of packaging film. The fact that L. monocytogenes increased whenever pseudomonads dominated, i.e. aerobic storage and MAP/VP in high-permeability film, and even earlier than on sterile tissue, suggests that this spoilage group enhanced growth of the pathogen. Brochothrix thermosphacta constituted the major proportion of the total microflora in MAP/VP within the low-permeability film, where no growth of L. monocytogenes was detected either on naturally contaminated or sterile meat fillets. The addition of 0.8% (v/w) oregano essential oil resulted in: (i) an initial reduction of 2-3 log10 of the majority of the bacterial population, with lactic acid bacteria and L. monocytogenes indicating the most apparent decrease in all gaseous environments, and (ii) limited growth aerobically and survival/death of L. monocytogenes in MAP/VP, regardless of film permeability.

Aerobiosis↗
PubMed2000

Development and evaluation of a model predicting the survival of Escherichia coli O157:H7 NCTC 12900 in homemade eggplant salad at various temperatures, pHs, and oregano essential oil concentrations.

Homemade eggplant salad, a traditional Greek appetizer, was inoculated with Escherichia coli O157:H7 NCTC 12900 supplemented with different concentrations of oregano essential oil (0.0, 0.7, 1. 4, and 2.1% [vol/wt]) and stored at different temperatures (0, 5, 10, and 15 degrees C). The product's pH was adjusted to 4.0, 4.5, or 5. 0 with lemon juice. For each combination of the environmental factors, the bacterial counts were modeled, using the Baranyi model, as a function of time to estimate the kinetic parameters of the pathogen. A reduction of more than 1 log unit in E. coli O157:H7 counts was observed in all cases, and the death rate depended on the pH, the storage temperature, and the essential oil concentration. Separate quadratic models were developed with natural logarithms of the shoulder period and death rate as estimated by the growth model, as a function of temperature, pH, and oregano essential oil concentrations. These were further used to predict the population of E. coli O157:H7 NCTC 12900 from other inoculated eggplant salads at random conditions of temperature, pH, and oregano oil concentration. The predicted values were compared with viable-count measurements for validation.

Colony Count, Microbial↗
PubMed2000

Applicability of an Arrhenius model for the combined effect of temperature and CO(2) packaging on the spoilage microflora of fish.

The temperature behavior of the natural microflora on the Mediterranean fish red mullet (Mullus barbatus) was examined as a case study. The growth of the spoilage bacteria Pseudomonas spp., Shewanella putrefaciens, Brochothrix thermosphacta, and lactic acid bacteria was modeled as a function of temperature and the concentration of carbon dioxide in modified atmosphere packaging. Combined models were developed and comparatively assessed based on polynomial, Belehradek, and Arrhenius equations. The activation energy parameter of the Arrhenius model, E(A), was independent of the packaging atmosphere and ranged from 75 to 85 kJ/mol for the different bacteria, whereas the preexponential constant decreased exponentially with the packaging CO(2) concentration. We evaluated the applicability of the models developed by using experimental bacterial growth rates obtained from 42 independent experiments performed with three Mediterranean fish species and growth rates predicted from the models under the same temperature and packaging conditions. The accuracy factor and bias factor were used as statistical tools for evaluation, and the developed Arrhenius model and the Belehradek model were judged satisfactory overall.

Animals↗
PubMed1999

Use of time-temperature integrators and predictive modelling for shelf life control of chilled fish under dynamic storage conditions.

A systematic approach for fish shelf life modelling and Time Temperature Integrator (TTI) selection in order to plan and apply an effective quality monitoring scheme for the fish chill chain was developed. The temperature behaviour of the natural microflora of the Mediterranean fish boque (Boops boops) was studied and growth of the specific spoilage bacteria Pseudomonas spp. and Shewanella putrefaciens was modelled and correlated to organoleptic shelf life. Arrhenius and square root functions were used to model temperature dependence of maximum growth rates. Bacterial growth and shelf life models were validated under dynamic storage conditions with independent variable temperature experiments. The response of several TTIs from similar storage experiments was also modelled. The reliability of the TTI monitoring was cumulatively expressed by the error in the TTI derived effective temperature (Teff) for different variable temperature distributions. Teff was directly translated to shelf life of the fish.

Animals↗
PubMed1999

A predictive model for the non-thermal inactivation of Salmonella enteritidis in a food model system supplemented with a natural antimicrobial.

Home-made taramasalad, a traditional Greek appetizer, was inoculated with Salmonella enteritidis supplemented with different concentrations of oregano essential oil (0.0, 0.5, 1.0, 2.0% v/w) and stored at different temperatures (5, 10, 15, 20 degrees C). The product's pH was adjusted from 4.3 to 5.3 with lemon juice. At each combination of the environmental factors, the bacterial counts were modelled as a function of time in order to estimate the kinetic parameters of the pathogen. For comparison, two different models were used. A reduction of Salmonella enteritidis was observed in all cases and its death rate depended on the pH, the storage temperature and the essential oil concentration. Death responses as a function of pH, storage temperature and concentration of oregano essential oil were described using a quadratic function which was then used to predict the death of Salmonella enteritidis in home-made taramasalad of different compositions.

Food Microbiology↗
PubMed1999

Chemical and sensory changes associated with microbial flora of Mediterranean boque (Boops boops) stored aerobically at 0, 3, 7, and 10 degreesC.

The development of a microbial population and changes in the physicochemical and sensorial characteristics of Mediterranean boque (Boops boops), called gopa in Greece, stored aerobically at 0, 3, 7, and 10 degreesC were studied. Pseudomonads and Shewanella putrefaciens were the dominant bacteria at the end of the storage period, regardless of the temperature tested. Enterobacteria and Brochothrix thermosphacta also grew, but their population density was always 2 to 3 log10 CFU g-1 less than that of pseudomonads. The concentration of potential indicators of spoilage, glucose and lactic acid, decreased while that of the alpha-amino groups increased during storage. The concentrations of these carbon sources also decreased on sterile fish blocks inoculated with strains isolated from fish microbial flora. The organic acid profile of sterile fish blocks inoculated with the above-mentioned bacteria and that of naturally spoiled fish differed significantly. An excellent correlation (r = -0.96) between log10 counts of S. putrefaciens or Pseudomonas bacteria with freshness was observed in this study.

Aerobiosis↗
PubMed1999

Biogenic amines and sensory changes associated with the microbial flora of Mediterranean gilt-head sea bream (Sparus aurata) stored aerobically at 0, 8, and 15 degrees C.

Changes in the concentrations of tyramine, agmatine, putrescine, cadaverine, spermidine, tryptamine, spermine, histamine, and trimethylamine were studied in parallel with the development of the microbial population during the storage of Mediterranean gilt-head sea bream (Sparus aurata) at three temperatures (0, 8, 15 degrees C). Changes in sensory scores were also recorded. Pseudomonads and H2S-producing bacteria were the dominant microorganisms. Enterobacteriaceae and lactic acid bacteria were also present in the fish microflora. Among the biogenic amines, putrescine and cadaverine were detected when pseudomonads exceeded 10(6) to 10(7) CFU/g. Histamine was produced only in samples stored at 15 degrees C. Tyramine, tryptamine, agmatine, and trimethylamine were absent regardless of the storage temperature.

Aerobiosis↗
PubMed1998

Modelling the effectiveness of a natural antimicrobial on Salmonella enteritidis as a function of concentration, temperature and pH, using conductance measurements.

The growth of Salmonella enteritidis in a brain heart infusion medium was monitored using the traditional viable count method and by conductance measurements using a Rabit impedance instrument. Growth curves (log10 cfu ml-1 vs time) at three different concentrations of oleuropein (0, 0.2 and 0.8%), pH values in the range of 5-8 and incubation temperatures from 22 to 42 degrees C were modelled using the Gompertz equation. A good correlation between the maximum growth rate from the viable count method and the maximum slope of the conductance curve from the impedance instrument was established. Based on this correlation, the maximum specific growth rate of Salm. enteritidis was modelled as a function of the oleuropein concentration, initial pH values and the incubation temperature with a quadratic equation, using a new, large dataset of growth measurements by conductance. The developed model was validated by statistical comparison of predicted growth rates with growth rates determined by the viable count method, within the limits of the antimicrobial, pH and temperature domain.

Colony Count, Microbial↗
PubMed1996

The effect of glucose supplementation on the spoilage microflora and chemical composition of minced beef stored aerobically or under a modified atmosphere at 4 degrees C.

Glucose was added to minced meat (pH 6.0) and stored under aerobic or a modified atmosphere (MA) composed of 80% O2 and 20% CO2 to assess the effects of carbohydrate on the microbial association and the chemical properties of the meat. The type of packaging affected the size and the final composition of the microflora. The microbial composition of the mince without added glucose in air or MA, given in log10 cfu/g respectively, were pseudomonads (9.8 and 7.3), Brochothrix thermosphacta (8.5 and 8.1), lactic acid bacteria (8.8 and 8.7), Enterobacteriaceae (7.2 and 6.1) and yeasts (4.3 and 4.2). In mince supplemented with 0.2% (w/w) glucose, similar composition and numbers were observed. Glucose, glucose 6-phosphate and lactic acid were consumed at slower rates by the flora on meat stored under MA than by the flora on meat stored in air. The addition of glucose enhanced gluconate production by the flora on meat stored in air. D-lactic and acetic acid were produced in all samples stored under the MA.

Aerobiosis↗
PubMed1996

Growth/survival of Salmonella enteritidis on fresh poultry and fish stored under vacuum or modified atmosphere.

The effect of vacuum and modified atmosphere packaging on the growth/survival of Salmonella enteritidis on fresh poultry and fish (Boops boops) is described. Salmonella enteritidis survived but did not grow significantly in all samples (poultry or fish) at 3 degrees C. At 10 degrees C the numbers of Salm. enteritidis increases rapidly in vacuum-packed samples and in samples flushed with 100% N2, 20% CO2/80% O2 of both types of proteinaceous food. Growth was also evident in fish and poultry flushed with 100% CO2; however the rate of growth was greater in fish samples rather than in poultry.

Animals↗