Inhibition of A. carbonarius growth and reduction of ochratoxin A by bacteria and yeast composites of technological importance in culture media and beverages.

Five composites of yeast and six of bacterial isolates from fermented products were studied, in order to assess their ability to inhibit Aspergillus carbonarius growth and reduce OTA concentration in culture media and beverages. The antagonistic effect of the above composites against A. carbonarius growth was studied in synthetic grape medium of pH 3.5 and a(w) 0.98, 0.95, 0.92 after incubation at 25°C. Different combinations of initial inocula of bacteria or yeast composites and fungi were used (10(2)cfu/mL vs 10(5)spores/mL; 10(5)cfu/mL vs 10(2)spores/mL; and 10(5)cfu/mL vs 10(5)spores/mL). Regarding the OTA reduction experiment, 10(3) and 10(7)cfu/mL of the bacteria and yeast composites were inoculated in liquid media of different pH (3.0, 4.0, 5.0, and 6.1 or 6.5) and initial OTA concentration (50 and 100µg/L) and incubated at 30°C. Moreover, grape juice, red wine, and beer were supplemented with 100µg/L of OTA and inoculated with composites of 16 yeasts (16YM) and 29 bacterial (29BM) strains (10(7)cfu/mL) to estimate the kinetics of OTA reduction at 25°C for 5days. Fungal inhibition and OTA reduction were calculated in comparison to control samples. None of the bacterial composites inhibited A. carbonarius growth. The high inoculum of yeast composites (10(5) cfu/mL) showed more efficient fungal inhibition compared to cell density of 10(2) cfu/mL. All yeast composites showed higher OTA reduction (up to 65%) compared to bacteria (2-25%), at all studied assays. The maximum OTA reduction was obtained at pH 3.0 by almost all yeast composites. For all studied beverages the decrease in OTA concentration was higher by yeasts (16YM) compared to bacteria (29BM). The highest OTA reduction was observed in grape juice (ca 32%) followed by wine (ca 22%), and beer (ca 12%). The present findings may assist in the control of A. carbonarius growth and OTA production in fermented foodstuffs by the use of proper strains of technological importance.

Evaluation of control over the microbiological contamination of carcasses in a lamb carcass dressing process operated with or without pasteurizing treatment.

The aim of this study was to quantify the hygienic status of a lamb slaughterhouse by means of multivariate statistical analysis, to demonstrate how the microbiological data could be exploited to improve the lamb slaughter process by constructing control charts and to evaluate the potential effect of an intervention step such as steam application on the microbiological quality of lamb carcasses. Results showed that pelt removal and evisceration were hygienically uncontrolled. TVC and Enterobacteriaceae progressively increased from the stage 'after pelt removal of hind and forelegs/before final pulling' to the stage 'after evisceration/before pluck removal' thus indicating possible deposition of microorganisms during these operations. It seems that the processing stages of freshly produced carcasses were better distinguished by Enterobacteriaceae, with evisceration contributing mostly to the final Enterobacteriaceae counts. Application of steam during the lamb slaughter process reduced microbial counts without adverse effects on the organoleptic characteristics of the carcasses. Moreover, the construction of control charts showed that decontamination with steam contributed to the maintenance of an in control process compared to that before the application of steam, suggesting the potential use of steam as an intervention step during the lamb slaughter process.

Quantifying the spoilage and shelf-life of yoghurt with fruits.

The aim of the present study was to develop a predictive model to quantify the spoilage of yoghurt with fruits. Product samples were stored at various temperatures (5-20 °C). Samples were subjected to microbiological (total viable counts, lactic acid bacteria-LAB, yeasts and moulds) and physico-chemical analysis (pH, titratable acidity and sugars). LAB was the dominant micro-flora. Yeasts population increased at all temperatures but a delay was observed during the first days of storage. Titratable acidity and pH remained almost constant at low temperatures (5 and 10 °C). However, at higher temperatures (>10 °C), an increase in titratable acidity and reduction in pH was observed. Sugar concentration (fructose, lactose and glucose) decreased during storage. A mathematical model was developed for shelf-life determination of the product. It was successfully validated at a temperature (17 °C) not used during model development. The results showed that shelf-life of this product could not be established based only on microbiological data and use of other parameters such as sensory or/and physico-chemical analysis is required. Shelf-life determination by spoilage tests is time-consuming and the need for new rapid techniques has been raised. The developed model could help dairy industries to establish shelf-life predictions on yoghurt with fruits stored under constant temperature conditions.

Adaptive growth responses of Listeria monocytogenes to acid and osmotic shifts above and across the growth boundaries.

The effect of acid and osmotic shifts on the growth of Listeria monocytogenes was evaluated at 10°C. Two types of shifts were tested: (i) within the range of pH and water activity (a(w)) levels that allow growth of L. monocytogenes and (ii) after habituation at no-growth conditions back to growth-permitting conditions. A L. monocytogenes cheese isolate, with high survival capacity during cheesemaking, was inoculated (10(2) CFU/ml) in tryptic soy broth supplemented with 0.6% yeast extract at six pH levels (5.1 to 7.2; adjusted with lactic acid) and 0.5% NaCl (a(w) 0.995), or four a(w) levels (0.995 to 0.93, adjusted with 0.5 to 10.5% NaCl) at pH 7.2 and grown to early stationary phase. L. monocytogenes was then shifted (at 10(2) CFU/ml) to each of the aforementioned growth-permitting pH and a(w) levels and incubated at 10°C. Shifts from no-growth to growth-permitting conditions were carried out by transferring L. monocytogenes habituated at pH 4.9 or a(w) 0.90 (12.5% NaCl) for 1, 5, and 10 days to all pH and a(w) levels permitting growth. Reducing a(w) or pH at different levels in the range of 0.995 to 0.93 and 7.2 to 5.1, respectively, decreased the maximum specific growth rate of L. monocytogenes. The lag time of the organism increased with all osmotic downshifts, as well as by the reduction of pH to 5.1. Conversely, any type of shift within pH 5.5 to 7.2 did not markedly affect the lag times of L. monocytogenes. The longer the cells were incubated at no-growth a(w) (0.90), the faster they initiated growth subsequently, suggesting adaptation to osmotic stress. Conversely, extended habituation at pH 4.9 had the opposite effect on subsequent growth of L. monocytogenes, possibly due to cell injury. These results suggest that there is an adaptation or injury rate induced at conditions inhibiting the growth of the pathogen. Thus, quantifying adaptation phenomena under growth-limiting environments, such as in fermented dairy and meat products or products preserved in brine, is essential for reliable growth simulations of L monocytogenes during transportation and storage of foods.

Modeling the effect of abrupt acid and osmotic shifts within the growth region and across growth boundaries on adaptation and growth of Listeria monocytogenes.

This study aims to model the effects of acid and osmotic shifts on the intermediate lag time of Listeria monocytogenes at 10°C in a growth medium. The model was developed from data from a previous study (C. I. A. Belessi, Y. Le Marc, S. I. Merkouri, A. S. Gounadaki, S. Schvartzman, K. Jordan, E. H. Drosinos, and P. N. Skandamis, submitted for publication) on the effects of osmotic and pH shifts on the kinetics of L. monocytogenes. The predictive ability of the model was assessed on new data in milk. The effects of shifts were modeled through the dependence of the parameter h(0) ("work to be done" prior to growth) induced on the magnitude of the shift and/or the stringency of the new environmental conditions. For shifts across the boundary, the lag time was found to be affected by the length of time for which the microorganisms were kept at growth-inhibiting conditions. The predicted concentrations of L. monocytogenes in milk were overestimated when the effects of this shift were not taken into account. The model proved to be suitable to describe the effects of osmotic and acid shifts observed both within the growth domain and across the growth boundaries of L. monocytogenes.

Distribution of aminogenic activity among potential autochthonous starter cultures for dry fermented sausages.

Any bacterial strain to be used as starter culture should have suitable characteristics, including a lack of amino acid decarboxylase activity. In this study, the decarboxylase activity of 76 bacterial strains, including lactic acid bacteria and gram-positive, catalase-positive cocci, was investigated. These strains were previously isolated from European traditional fermented sausages to develop autochthonous starter cultures. Of all the strains tested, 48% of the lactic acid bacteria strains and 13% of gram-positive, catalase-positive cocci decarboxylated one or more amino acids. Aminogenic potential was strain dependent, although some species had a higher proportion of aminogenic strains than did others. Thus, all Lactobacillus curvatus strains and 70% of Lactobacillus brevis strains had the capacity to produce tyramine and beta-phenylethylamine. Some strains also produced other aromatic amines, such as tryptamine and the diamines putrescine and cadaverine. All the enterococcal strains tested were decarboxylase positive, producing high amounts of tyramine and considerable amounts of beta-phenylethylamine. None of the staphylococcal strains had tyrosine-decarboxylase activity, but some produced other amines. From the aminogenic point of view, Lactobacillus plantarum, Lactobacillus sakei, and Staphylococcus xylosus strains would be the most suitable for use as autochthonous starter cultures for traditional fermented sausages.

Quantitative microbiological risk assessment as a tool to obtain useful information for risk managers--specific application to Listeria monocytogenes and ready-to-eat meat products.

The presence of Listeria monocytogenes in a sliced cooked, cured ham-like meat product was quantitatively assessed. Sliced cooked, cured meat products are considered as high risk products. These ready-to-eat, RTE, products (no special preparation, e.g. thermal treatment, before eating is required), support growth of pathogens (high initial pH=6.2-6.4 and water activity=0.98-0.99) and has a relatively long period of storage at chilled temperatures with a shelf life equal to 60 days based on manufacturer's instructions. Therefore, in case of post-process contamination, even with low number of cells, the microorganism is able to reach unacceptable levels at the time of consumption. The aim of this study was to conduct a Quantitative Microbiological Risk Assessment (QMRA) on the risk of L. monocytogenes presence in RTE meat products. This may help risk managers to make decisions and apply control measures with ultimate objective the food safety assurance. Examples are given to illustrate the development of practical risk management strategies based on the results obtained from the QMRA model specifically developed for this pathogen/food product combination.

Control of spoilage microorganisms in minced pork by a self-developed modified atmosphere induced by the respiratory activity of meat microflora.

The changes in microbial flora of minced pork during aerobic storage at 0, 5, 10 and 15 degrees C were studied. Minced pork samples (100g) were packed using two types of packaging films: (a) a common food film with high permeability (HPF) and (b) a film with low permeability (LPF). The respiratory activity of meat microflora and the use of a LPF resulted in a modified atmosphere in the package headspace developed during storage. Oxygen concentration decreased from 18.7% (after packaging) to 7% (after 15 days of storage) in packages with LPF, stored at 0 degrees C, while CO(2) increased from 3% to 10.5%, respectively. On the contrary, no significant atmosphere changes were observed during storage of HPF packages. The self-developed modified atmosphere in LPF packages resulted in a significant inhibition of pseudomonad growth which was more pronounced at low storage temperatures. For example, during storage at 0 degrees C, the growth rate of pseudomonads in meat packed with LPF was reduced by 48.7% compared to HPF. At 10 degrees C the latter reduction decreased to 13.7%. LPF packaging was also found to inhibit the growth of Brochothrix thermosphacta but this inhibition was weaker compared to pseudomonads. The effect of storage temperature on the growth rate of pseudomonads and B. thermosphacta in minced pork packed with the different films was modeled using an Arrhenius equation. For both bacteria, the activation energy was higher for LPF packaging. This can be attributed to the increased inhibitory effect of the modified atmosphere at lower storage temperature. The Arrhenius model was further used to evaluate the effect of temperature on the time required by the two bacteria to reach a spoilage level of 10(7)CFU/g. The results showed that when LPF packaging is combined with effective temperature control the time-to-spoilage can be significantly extended compared to HPF packaging.

Risk profiles of pork and poultry meat and risk ratings of various pathogen/product combinations.

Risk profiles of pork and poultry meat were carried out using an Excel-based software program, Risk Ranger. It is a semi-quantitative risk estimator answering various questions relating to the probability of exposure to a hazard, susceptibility of the population of interest, severity of the illness caused by the hazard if present and probability of food containing an infectious dose. Therefore, qualitative and quantitative inputs were used to estimate and rank the risk of various hazards/food combinations. Risk scores provided by the tool were characterized as low, medium and high. Also, health risk was estimated separately, where needed, for low and high risk populations. Low risk scores were obtained for Salmonella spp., Listeria monocytogenes and enterohaemorrhagic Escherichia coli (EHEC) for low risk population. High risk scores were obtained for hepatitis E virus (HEV) in raw pork products (both low and high risk populations). Moderate risk scores for Salmonella spp. and L. monocytogenes in processed pork or poultry-meat products (ready-to-eat or to be reheated) and partially cooked pork products were also obtained (low risk population). Scores for Staphylococcus aureus, Clostridium perfringens and Bacillus cereus and various product types were mostly in the "medium" risk category, except for S. aureus/ready-to-eat pork products able to support growth of the organism, which fell into the high risk category. Campylobacter spp. gave moderate risk scores with one exception (raw poultry products), whereas Y. enterocolitica showed combinations of low risk and few of medium risk. High risk pathogen/product combinations identified were: 1) temperature abused, ready-to-eat pork and/or poultry-meat products with extended shelf life and cross-contaminated by L. monocytogenes (high risk population), EHEC (high risk population) or S. aureus (all population), 2) partially cooked or processed intended to be reheated pork products cross-contaminated by L. monocytogenes, served undercooked and receiving improper cooling or reheating (high risk population), and 3) all people consuming undercooked meals cross-contaminated with Campylobacter spp. (e.g. from raw poultry and raw poultry-meat products) and HEV (e.g. from raw pork and raw pork-meat products). Salmonellae gave high risk scores in all food categories (except preserved meat products) for high risk population. Preserved meats (mainly pork) such as dry fermented sausages gave low risk scores. Only Salmonella spp., L. monocytogenes and E. coli EHEC gave moderate risk ratings in case of ingredients likely to be contaminated at an early stage of processing (e.g. animal at slaughter) and inadequate fermentation process. These results may constitute a source of information for hazard assessment during application of a Food Safety Management System.

Purification and characterization of a bacteriocin produced by Leuconostoc mesenteroides E131.

Leuconostoc mesenteroides E131, isolated from Greek traditional fermented sausage, prepared without the addition of starters, produces a bacteriocin which is active against the pathogen Listeria monocytogenes. The bacteriocin was purified by 50% ammonium sulphate precipitation, cation exchange, and reverse-phase chromatography. Bacteriocin is active at pH values between 4.0 and 9.0 and retains activity after incubation for 1h at 100°C. Proteolytic enzymes inactivated the bacteriocin after 1h of incubation, while renin resulted in full inactivation only after 24h. Lipase resulted in full inactivation after 4h. Applying molecular methods, it was determined that the bacteriocin produced, named as mesenterocin E131, was identical to mesenterocin Y105 and was expressed during the exponential growth phase.

Traditional dry fermented sausages produced in small-scale processing units in Mediterranean countries and Slovakia. 1: Microbial ecosystems of processing environments.

Microbial ecosystems were surveyed in 314 environmental samples from 54 Southern and Eastern European small-scale processing units (PUs) manufacturing traditional dry fermented sausages. The residual microflora contaminating the surfaces and the equipment were analysed after cleaning and disinfection procedures. All the PU environments were colonised at various levels by spoilage and technological microflora with excessive contamination levels in some of the PUs. Sporadic contamination by pathogenic microflora was recorded. Salmonella and Listeria monocytogenes were detected in 4.8% and 6.7% of the samples, respectively, and Staphylococcus aureus was enumerated in 6.1% of the samples. Several critical points were identified, such as the machines for S. aureus and the tables and the knives for L. monocytogenes; this knowledge is crucial for the improvement of hygiene control systems in small and traditional meat processing industries. The variability of the residual contamination emphasized the different cleaning, disinfecting and manufacturing practices routinely followed by these small-scale processing units.

Determination of the growth limits and kinetic behavior of Listeria monocytogenes in a sliced cooked cured meat product: validation of the predictive growth model under constant and dynamic temperature storage conditions.

To describe the growth limits of Listeria monocytogenes NCTC10527 in a sliced vacuum-packaged cooked cured meat product, the binary logistic regression model was used to develop an equation to determine the probability of growth or no growth of L. monocytogenes as a function of temperature (from 0 to 10 degrees C) and water activity (from 0.88 to 0.98). Two inoculum concentrations were used (10 and 10(4) CFU g(-1)), and the growth limits for the two inocula were different. The kinetic behavior of L. monocytogenes as a function of temperature (4, 8, 12, and 16 degrees C) on the same meat product at the lower concentration (10 CFU g(-1)) was also studied. The Baranyi model appeared to fit the overall experimental data better than did the modified Gompertz and the modified logistic models. Maximum specific growth rate (micromax), lag phase duration (LPD), and maximum cell concentration (Nmax) derived from the primary model were modeled using the square root function (micromax and LPD) and a second order polynomial (Nmax) (secondary models). The selection of the best model (primary or secondary) was based on some statistical indices (the root mean square error of residuals of the model, the regression coefficient, the F test, the goodness of fit, and the bias and accuracy factor). The developed kinetic behavior model was validated under constant and dynamic temperature storage conditions. This prediction of L. monocytogenes growth provides useful information for improving meat safety and can be used for in-depth inspection of quality assurance systems in the meat industry.

Modeling of growth and bacteriocin production by Leuconostoc mesenteroides E131.

Leuconostoc mesenteroides E131, isolated from dry fermented sausages, produces an antimicrobial agent, characterized as bacteriocin. The effect of pH and temperature on growth and bacteriocin production, using MRS broth as growth medium, was studied in a fermentor. The pH value at which the best cell growth was observed (6.5) did not coincided with the value at which the maximum bacteriocin activity was attained (5.5). In contrast, the maximum bacteriocin activity was attained at temperature (25°C) close to the optimum temperature for cell growth (25-30°C). Notably, the range of pH and temperature for good bacteriocin production was within the range used for sausage fermentation. An empirical model was developed to describe the growth and bacteriocin production in different pH and temperature conditions. The model was able to describe growth and bacteriocin production and it could be used to predict the kinetic parameters of growth and bacteriocin production within the pH and temperature range examined.

Growth and bacteriocin production kinetics of Leuconostoc mesenteroides E131.

AIMS: The aim of this study was to investigate the effect of pH, temperature, sodium chloride, type and level of sugar used in fermented sausages, on the occurrence and the concentration of the maximum bacteriocin activity, in order to optimize the bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides E131. METHODS AND RESULTS: In order to study the effect of the environmental factors on growth and bacteriocin production of Leuc. mesenteroides E131 fermentations were carried out in fermentor as well as in flasks. Mathematical equations were used to describe the kinetic parameters of the strain. When the micro-organism was grown in lower pH value (5.5) than optimum for growth (pH 6.5) the bacteriocin production was enhanced. On the contrary, bacteriocin production was favoured when the micro-organism was grown at temperatures close to the optimum for growth (25 degrees C). Finally, the level and the type of the sugar used as carbon source affected both growth and bacteriocin production with glucose being better source for biomass production and fructose more suitable for bacteriocin production. CONCLUSIONS: Leuconostoc mesenteroides E131 has a potential use as protective culture or its bacteriocin as protective agent in combination with another starter culture in fermented meats. SIGNIFICANCE AND IMPACT OF THE STUDY: Better understanding of the influence of environmental factors, such as pH, temperature and carbon source on the kinetic behaviour of Leuc. mesenteroides E131.

Characterization of the microbial flora from a traditional Greek fermented sausage.

The microbial flora of naturally fermented sausages was studied. Lactic acid bacteria were the dominant species at the end of fermentation in all 3 batches (ca. 10(8) cfu g(-1)). Enterobacteria, Pseudomonas, yeasts and aerobic spore-formers decreased during fermentation and the ripening process and were below the detection limit in the end product. Enterococci exceeded 10(4)-10(5) cfu g(-1) during fermentation and remained constant at this level during ripening. Gram-positive, catalase-positive cocci exceeded 10(5) cfu g(-1), except for batch 1, during the first days of fermentation and then decreased until the end of ripening (10(2)-10(4) cfu g(-1)). No pathogenic staphylococci, sulfite reducing clostridia or Salmonella spp. were detected. Listeria spp. occurred in the first days of fermentation but were eliminated by the end of whole process in all batches. Identification showed that the majority of lactobacilli isolated from MRS agar strains were assigned to the species of Lactobacillus plantarum and Lb. plantarum/pentosus. All the isolated strains from the mannitol salt agar belonged to the genus of Staphylococcus. The predominant species were Staphylococcus saprophyticus, Staphylococcus xylosus and Staphylococcus simulans. The tests used to characterize the lactic acid bacteria and staphylococci as well as their distribution on the three batches were also discussed.

Influence of nutrients on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442.

The aim of this study was to investigate the effect of complex nutrients on microbial growth and bacteriocin production, in order to improve bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442. The fermentations were conducted at the optimum pH and temperature for bacteriocin production (pH 5.5+/-0.1 and temperature 25+/-0.1 degrees C). Because of their association with the final biomass, conditions favouring the increase of the produced biomass resulted in the increase of bacteriocin activity in the growth medium. Since the produced final biomass and the final concentration of the bacteriocins were associated with the amount of the carbon (glucose) and nitrogen source, better growth of the lactic acid bacterial strains favoured the increase of the specific bacteriocin production. Additionally, the bacteriocin production was influenced by carbon/nitrogen ratio.

Influence of pH and temperature on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442.

The aim of this study was to investigate the relationship between the microbial growth, the bacteriocin production and the effect of pH and temperature on the occurrence and the concentration of the maximum activity, to optimize the bacteriocin synthesis during the growth cycle. Two bacteriocins produced by lactic acid strains Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442 were studied. A slight increase of the final biomass resulted in the improvement of the bacteriocin activity in the growth medium under controlled pH (5.0 and 5.5). Temperature and pH had a significant effect on the production of the two bacteriocins and was enhanced by the relatively low growth rates. The optimum production conditions of the bacteriocins did not coincide with those for growth. The optimum pH and temperature values for growth were 6.0-6.5 and 30 °C and for bacteriocin production were 5.5 and 25 °C.

Microbial interaction in cooked cured meat products under vacuum or modified atmosphere at 4 degrees C.

AIMS: To investigate the antagonistic activity of two lactic acid strains against the spoilage microflora in cooked cured meat products, vacuum or modified atmosphere packed at 4 degrees C and to determine the inhibitory capacity of their bacteriocins. METHODS AND RESULTS: Frankfurter-type sausages and sliced cooked cured pork shoulder were inoculated with Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442 or with their bacteriocins. The microbial, physico-chemical (pH, L- and D-lactate, acetate and ammonia) and colour changes were studied. Results under vacuum packaging showed that in the uninoculated samples of the pork product the spoilage microflora grew but in the inoculated ones the spoilage microorganisms (e.g. Brochothrix thermosphacta and enterococci) reduced during the storage. This observation was more pronounced in the samples with the addition of bacteriocins. In the frankfurter-type sausages the spoilage microflora did not grow in the uninoculated and inoculated samples. In the modified atmosphere enriched in CO2 the population of spoilage microflora remained at low levels in both products, indicating that CO2 has an effect on the spoilage microorganisms' growth. In the pork product the concentrations of acetate and d-lactate increased while L-lactate decreased, but in the frankfurter-type sausages increase of acetate and D-lactate was not observed. CONCLUSIONS: Lactic acid strains had an effect on the spoilage microflora growth but did not affect, negatively, the organoleptic properties of the products. These strains may be used as biopreservative cultures or their bacteriocins could be an important contribution to microbiological quality of meat products. SIGNIFICANCE AND IMPACT OF STUDY: Establishment of biopreservation as a method for extension of shelf life of meat products.

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.

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.