The use of rosemary extract in combination with nisin to extend the shelf life of pompano (Trachinotus ovatus) fillet during chilled storage

The effects of rosemary extract (RE) combined with nisin (N) on the quality of pompano (Trachinotus ovatus) were assessed throughout 15 days of storage at 4 ± 1 °C. Physicochemical (peroxide value, thiobarbituric acid, total volatile basic nitrogen, trimethylamine, pH, K value, texture, and color), sensory, and bacteriological characteristics of fish fillet were all periodically analyzed. RE + N treatment effectively improved physicochemical quality parameters and the sensory, and reduced microbial growth as compared with either treatment of RE or N alone or the control, which resulted in a significant extension in the shelf life of pompano fillet. Therefore, rosemary extract combined with nisin treatment may be a promising method of maintaining the storage quality and extending shelf life of pompano fillet during chilled storage.     

Photocatalytic degradation of methylene blue and inactivation of Gram-negative bacteria by TiO2 nanoparticles in aqueous suspension

The photocatalytic degradation of methylene blue (MB) and inactivation of Gram-negative bacteria Escherichia coli (generic) and Pseudomonas aeruginosa by TiO₂ nanoparticles in aqueous suspension were studied. TiO₂ resulted in significant reduction in MB absorption and a shift of MB absorption peak from 664 nm to 658 nm after a short time of irradiation. The maximum degradation of MB was observed when the concentration of TiO₂ in the aqueous suspension was 0.5 g L⁻¹. TiO₂ was also very effective with inhibiting growth of both Gram-negative bacteria E. coli and P. aeruginosa, although it took more than 60 min to observe the inactivation effects. The photocatalytic inactivation toward E. coli and P. aeruginosa by TiO₂ showed a similar trend with much higher effectiveness toward E. coli under the same experimental conditions. The inactivation kinetic behaviors could be explained by the modified Langmuir–Hinshelwood model, and well fitted to a pseudo-first order kinetic equation. The reaction rate constant for E. coli and P. aeruginosa were 7.768 × 10⁶ cfu mL⁻¹ min⁻¹ and 5.655 × 10⁶ cfu mL⁻¹ min⁻¹, respectively. The adsorption equilibrium constant for E. coli was 1.053 × 10⁻⁸ mL cfu⁻¹, while it was 1.438 × 10⁻⁸ mL cfu⁻¹ for P. aeruginosa. These results further demonstrate that in an aqueous system, TiO₂ nanoparticles can effectively both degrade organic compounds and inhibit Gram-negative bacteria under UVA light. Compared with the degradation activity of TiO₂ toward organic compounds, its antimicrobial activity against Gram-negative bacteria would be delayed by 60 min. The antimicrobial activity of TiO₂ against Gram-negative bacteria could vary with bacterial species.     

Antimicrobial effect of cranberry juice and extracts

The antimicrobial effect of cranberry juice and of three cranberry extracts (water-soluble (E1) and apolar phenolic compounds (E2), and anthocyanins (E3)) was investigated against seven bacterial strains (Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, Escherichia coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442, Salmonella Typhimurium SL1344, and Staphylococcus aureus ATCC 29213). Each cranberry sample was analyzed to determine the minimum inhibitory concentration (MIC) and the maximal tolerated concentration (MTC) at neutral pH. The results, reported in μg phenol/mL, indicated that all the bacterial strains, both Gram-positive and Gram-negative, were selectively inhibited by the cranberry phenolic compounds. The extract rich in water-soluble phenolic compounds caused the most important growth inhibitions. The bacteria ERV, and to a lesser degree, P. aeruginosa, S. aureus and E. coli ATCC 25922, were the most sensitive to the antimicrobial activity of extract E1. The growth of P. aeruginosa and E. coli ATCC was also affected by the presence of the anthocyanin-rich cranberry extract E3, although the observed antibacterial effect was not as important as with extract E1. In general, L. monocytogenes, E. coli O157:H7 and S. Typhimurium were the most resistant to the antibacterial activity of the cranberry extracts. Within 30 min of exposure with pure neutralized cranberry juice, L. monocytogenes and ERV were completely inactivated.     

Carvacrol as potential quorum sensing inhibitor of Pseudomonas aeruginosa and biofilm production on stainless steel surfaces

Pseudomonas aeruginosa biofilm confers resistance to antibiotics and biocides; therefore, it represents a problem to clinical and industrial settings. This bacterial organization is controlled by quorum sensing (QS), which depends of autoinducer molecules, e.g. acyl-homoserine-lactones that regulate production on virulence factors as pyocyanin. As a solution to this problem, carvacrol, present in most of the antibacterial essential oils could be a potential agent to inhibit QS for its ability to interact with cell membrane and protein receptors involved in biofilm formation. Therefore, this work evaluated the effect of carvacrol on pyocyanin production and biofilm formation of P. aeruginosa. Minimal inhibitory concentration (MIC) of carvacrol against planktonic P. aeruginosa was 7.9 mM; in addition, carvacrol was tested against Chromobacterium violaceum as model for anti-QS agents, showing a MIC of 0.7 mM. Lower concentrations of carvacrol to observed MICs were applied to observe changes in QS activity and biofilm production to avoid effect of cell death on mentioned parameters. Carvacrol inhibited P. aeruginosa biofilms (1.5–3 Log CFU/cm²) at 0.9–7.9 mM, compared to non-treated bacteria on stainless steel surface. Pyocyanin production by P. aeruginosa was reduced up to 60% at 3.9 mM of carvacrol. Higher doses of carvacrol affected P. aeruginosa viability. Similar results were obtained for violacein production that is related to QS of C. violaceum, where carvacrol reduced up to 50% at 0.7 mM without affecting cell viability. These results showed that the inhibition of QS could be related with reduction of bacterial virulence and biofilm formation on stainless steel surfaces exposed to carvacrol.     

Monitoring the bacteriological quality of Italian bottled spring water from dispensers

The bacteriological quality of unprocessed bottled spring water was evaluated, through enumeration of heterotrophic plate count at 22 °C and 37 °C, total coliforms, Escherichia coli, intestinal enterococci and Pseudomonas aeruginosa. The aims of the research were to monitor the hygiene of bottled spring water and to evaluate the effectiveness of the dispenser sanitation procedure, reproducing field conditions. In total, 120 water samples were analyzed. The results indicated a high contamination frequency with P. aeruginosa (57.5%) and therefore the need to refine hygiene in the bottling plant and in the dispenser sanitation procedures.     

Polyphenolic extract from Rosa rugosa tea inhibits bacterial quorum sensing and biofilm formation

Quorum sensing (QS) is an intercellular signaling and gene regulatory mechanism, which is implicated in bacterial pathogenicity and food spoilage. Therefore, blocking bacterial QS system may prevent QS-controlled phenotypes responsible for food spoilage. In the present study, we aimed to investigate the anti-biofilm and quorum sensing inhibitory potentials of Rosa rugosa tea polyphenol (RTP) extract, which is rich in polyphenols (87.52%) and flavonoids (61.03%). The RTP specifically inhibited QS-controlled violacein production in Chromobacterium violaceum 026 with 87.56% reduction without significantly affecting its growth. Moreover, RTP exhibited inhibition in swarming motility (84.90% and 78.03%) and biofilm formation (67.02% and 72.90%) of Escherichia coli K-12 and Pseudomonas aeruginosa PAO1 in a concentration-dependent manner, respectively. These findings strongly suggest that RTP potentially could be developed as a new QS inhibitor and/or anti-biofilm agent to enhance the shelf life and increase food safety.     

Mathematical modeling and growth kinetics of Clostridium sporogenes in cooked beef

Clostridium sporogenes PA 3679 is a common surrogate for proteolytic Clostridium botulinum for thermal process development and validation. However, little information is available concerning the growth kinetics of C. sporogenes in food. Therefore, the objective of this study was to investigate the growth kinetics of C. sporogenes in cooked beef under different temperature conditions.Ground beef samples, inoculated with C. sporogenes spores, were incubated at temperatures between 8 and 47 °C to examine the growth of this microorganism. Two primary models (Huang and Baranyi models) were used to analyze the growth data. The Ratkowsky square-root model was used as the secondary model to evaluate the effect of temperature on bacterial growth rate and lag time. The USDA IPMP 2013, a free data analysis tool for predictive microbiology, was used in data analysis.No growth of C. sporogenes was observed at temperatures below 15 °C for up to 25 days. At temperatures between 20 and 47 °C, C. sporogenes grew in cooked beef. The growth curves could be analyzed by both Huang and Baranyi models. The root mean squared error (RMSE) was 0.375 for the Huang model, and 0.441 for the Baranyi model with a global h₀ of 10.46. The nominal minimum growth temperature (T₀) estimated from the Huang model was 15.5 °C, which was 12.7 °C for the Baranyi model. The maximum growth temperature was 48.0 and 48.3 °C for the Baranyi and Huang models, respectively. The lag times and specific growth rates of C. sporogenes observed in this study were reasonably close to the data reported in the literature for C. botulinum under comparable conditions, suggesting that C. sporogenes may be used as a potential surrogate for evaluating the growth of C. botulinum in cooked meats during cooling. However, a direct comparison of growth kinetics between the two microorganisms is needed to confirm the suitability of C. sporogenes as a surrogate of C. botulinum.     

Selection of Pseudomonas aeruginosa for biosurfactant production and studies of its antimicrobial activity

Biosurfactants are generally microbial metabolites with the typical amphiphilic structure of a surfactant. This study investigated potential biosurfactants production of Pseudomonas aeruginosa ATCC-10145 and Bacillus subtilis NCTC-1040 using glucose and n-hexadecane as substrates separately and compared it with the production in conventional medium. Pseudomonas aeruginosa growing in BHMS (Bushnell hass mineral salt) medium with glucose as substrate decreased the surface tension from 72 of distilled water to 32 mN/m, this strain had higher reduction than Bacillus subtilis among all the substrates tested. The selection of Pseudomonas aeruginosa for the separation of biosurfactant was determined. The crude biosurfactant was extracted from the supernatant and the yield of the crude biosurfactant was about 1 g/l. Some surface properties of rhamnolipids biosurfactant were evaluated. It also showed antimicrobial activity against different bacteria and fungi strains. The crude biosurfactant showed good action as antimicrobial activity against different bacterial and fungal species.     

Modelling the interaction of storage temperature,pH, and water activity on the growth behaviour of Listeria monocytogenes in raw and pasteurised semi-soft rind washed milk cheese during storage following ripening

The objective of this study was to investigate the growth of Listeria monocytogenes in semi-soft rind washed cheese made from raw and pasteurised milk at different storage temperatures (4, 10 and 15 °C) over a 28 day period simulating storage following ripening. Changes in water activity (a_w) and pH in cheeses were also monitored during storage. Response surface models were used to model the interaction of storage temperature and time on a_w, pH and L. monocytogenes population. Growth curves were fitted using Baranyi, modified Gompertz and Logistic models at all storage temperatures for both cheeses, and model parameters were statistically analysed. In raw and pasteurised milk cheeses, all models showed a significant (P < 0.05) increase in the specific growth rate (SGR, Day⁻¹) of L. monocytogenes with an increase in storage temperature. A higher SGR was observed for L. monocytogenes in pasteurised milk cheese (0.18–0.85 Day⁻¹) compared to raw milk cheese (0.05–0.37 Day⁻¹) at all storage temperatures studied. Response surface models indicated an increase in the L. monocytogenes population and pH with an increase in storage temperature. However, a decreasing trend in a_w for both cheese types was observed. The predicted regression model parameters for both the raw and pasteurised milk cheese showed a high correlation coefficient R² > 0.87. Overall, the L. monocytogenes population increased up to 3 log₁₀ cfu⁻g⁻¹ for both cheeses during storage following ripening. The fitted models confirmed different L. monocytogenes growth behaviour between raw and pasteurised milk cheeses, which could support the Food Business Operator in predicting growth during storage following ripening.     

Growth of Listeria monocytogenes in salmon roe – A kinetic analysis

The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 °C, were analyzed by curve-fitting to the Huang and Baranyi models using the USDA IPMP 2013. The experimental results showed that L. monocytogenes in salted samples exhibited approximately 40% longer lag times than the cells in unsalted samples under the same temperature condition, while the rates of bacterial growth were not affected by the addition of salt. The Ratkowsky square-root (RSR) model, Huang square-root (HSR) model, and an Arrhenius-type model were all shown suitable for evaluating the effect of temperature on specific growth rates. The estimated nominal minimum growth temperature in the RSR model was −0.5 °C, whereas the minimum growth temperature in HSR model was 2.57 °C. The HSR models may be more suitable for describing the temperature effect in salted salmon roe. The lag times of L. monocytogenes were found to change log-linearly with the specific growth rates. The mean h₀ in the Baranyi model was 0.742 in unsalted samples and 1.193 in salted samples, and did not appear to change with temperature in a systematic manner. In summary, kinetic models were developed for examining the effect of temperature on growth of L. monocytogenes in unsalted and salted salmon roe samples. The results may be used by the food industry and regulatory agencies to estimate the growth of L. monocytogenes in salmon roe, and to conduct risk assessments of this microorganism.     

A simple method to evaluate the shelf life of refrigerated rabbit meat

The shelf life of rabbit meat during refrigerated storage was investigated under industrial conditions. Rabbit carcasses were bulk packed (BP), packed under air (PUA) and under modified atmosphere (MAP) (30% O₂:40% CO₂:30% N₂). The main groups studied were mesophilic aerobes, psychrotrophic aerobes, Pseudomonas spp., lactic acid bacteria, yeast and moulds and Enterobacteriaceae. The microorganisms that showed faster growth were psychrotrophic aerobes (growth rate of 0.36 ± 0.09 day⁻¹) for BP, Pseudomonas (0.26 ± 0.03 day⁻¹) for PUA, and lactic acid bacteria (0.22 ± 0.01 day⁻¹) for MAP, and the lag phases were 4, 4 and 8 days, respectively. The main effect of MAP was the increase in lag phase from 4 to 8 days, for lactic acid bacteria, psychrotrophic and mesophilic aerobes. The respective growth rates were similar to those observed with PUA. In addition, MAP inhibited Pseudomonas growth during 18 days. Considering 6 log CFU g⁻¹ as maximum tolerable microbial load, the calculated values of shelf life in BP, PUA and MAP were 6, 7 and 12 days, respectively, when considering the fastest growing microorganisms.     

On the behavior of Listeria innocua and Lactobacillus acidophilus co-inoculated in a dairy dessert and the potential impacts on food safety and product's functionality

This study aimed to evaluate the behavior of Listeria innocua in a dairy dessert in the presence/absence of a probiotic microorganism and to assess the in vitro functionality of the probiotic dairy dessert. Three formulations of dairy dessert were prepared: F₁ – inoculated with Lactobacillus acidophilus La-5, F₂ – inoculated with L. innocua and F₃ – inoculated with both L. innocua and L. acidophilus La-5. The dairy desserts were stored at 5 °C/28 days, following measurement of the pH and enumeration of L. innocua and L. acidophilus La-5 on days 0, 7, 14, 21 and 28. The results showed that the pH of the formulation inoculated with L. acidophilus La-5 (F₁) has decreased to 5.6 at the end of the shelf life, while in F₂ (inoculated with L. innocua only) and F₃ (inoculated with L. innocua and L. acidophilus La-5) the pH increased. The counts of L. acidophilus La-5 decreased in F₁ throughout the shelf life, while in F₂ and in F₃, the populations of L. innocua increased, reaching up to 10^8–9 CFU/g at the end of shelf life. The functionality tests indicated that the percentage of survivors decreased (p < 0.05) from 89.3% to 58.8% in F₁ during storage shelf life, while an increase in the percentage of survival of L. acidophilus La-5 (94.0–99.1%, p < 0.05) was observed in F₃. The results of the present study highlight the needs to strictly ensure the microbiological safety of raw materials, control the pasteurization temperature and to guarantee that surfaces and environments are adequately cleaned and sanitized to avoid contamination by Listeria spp., and particularly, by Listeria monocytogenes. Further studies should be carried out to understand the interaction between L. innocua and L. acidophilus La-5.     

Biofilm formation of meat-borne Salmonella enterica and inhibition by the cell-free supernatant from Pseudomonas aeruginosa

Using polystyrene surfaces for attachment, we evaluated biofilm formation and cell surface hydrophobicities of 17 Salmonella enterica strains (belonging to 9 different serovars), and further assessed the effect of cell-free culture supernatants (CFS) from Pseudomonas aeruginosa (containing acylated homoserine lactones (AHLs)), on the growth and biofilm development of S. enterica. The results indicated that most of the 17 strains readily formed biofilms on polystyrene surfaces, but the development of biofilms were significantly influenced by serovars and incubation conditions. Strains of S1 (S. London), S2 (S. London), S9 (S. Indiana) and S16 (S. Typhimurium) produced greater biofilms regardless of the tested conditions compared with other strains, with maximum biofilm production of 3.08, 2.47, 2.21 and 3.39 (crystal violet assay), respectively. Significant differences in cell hydrophobicity were observed between strains, S16 (S. Typhimurium) showed highest hydrophobicity values (>56%) compared with the other strains (<46%). A significant positive correlation was observed between cell surface hydrophobicity and the capacity of individual strains to form biofilms. The presence of 30% and 60% CFS from P. aeruginosa (containing AHLs identified by thin-layer chromatography), significantly decreased the growth rates of S. enterica (S1, S9 and S16) during the exponential phase, but not during the stationary phase, and significantly inhibited biofilm development of S. enterica strains (S1, S9 and S16) when incubated both in tryptic soytone broth (TSB) and meat thawing loss broth (MTLB), reaching maximum inhibition percentage of 70.7 and 93.3, respectively. Our findings are therefore important for developing innovative control strategies of Salmonella biofilms.     

Estimation of growth parameters of Listeria monocytogenes after sublethal heat and slightly acidic electrolyzed water (SAEW) treatment

Time to detection experiments (TTD) based on turbidometry using an automatic Bioscreen C is a useful and straightforward method for estimating microbial growth parameters (lag time (λ), growth rate (μ) and “work to be done” (h₀)) at constant temperature. This study investigated the effects of slightly acidic electrolyzed water (SAEW) and heat treatment on Listeria monocytogenes growth at different recovery temperatures (10 °C, 15 °C, 25 °C, and 30 °C). Similar surviving and sublethally injured L. monocytogenes populations were obtained by heat treatment (55 °C for 10 min) and SAEW treatment (available chlorine concentration of 30 mg/l and ratio of bacteria against SAEW of 8:2 for 30 s). In these experimental conditions, stresses had greater impact on the λ and h₀ parameter in comparison with recovery temperature while there was no great change in growth rate under isothermal conditions. Larger λ values and h₀ parameters were observed in sublethal-heat injured L. monocytogenes (the maximum λ and h₀ parameters are 30.199 h and 1.6492) as compared to SAEW groups (the maximum λ and h₀ parameters are 22.634 h and 1.4396). The sensitivity analysis of SAEW and heat treatments on h₀ parameter indicated that SAEW treatment showed a higher influence. The collinearity diagnostics of independent variables [recovery temperature (T), μ, λ] for dependent variable (h₀ parameter) demonstrated that T, μ and λ had strong collinearity. In addition, the established secondary models in this study have good performances on predicting the effect of recovery temperature on bacterial growth parameters.     

Evaluation of the antimicrobial and antioxidant activities of essential oils, extracts and their main components from oregano from Madeira Island, Portugal

Origanum vulgare subsp. virens growing wild in Madeira Island, Portugal was studied within the ongoing investigations on polymorphic Lamiaceae species. The antimicrobial activity of the essential oils and n-hexane extracts of origanum was determined against 10 strains of bacteria and yeasts, found as human pathogenic or food spoilage microorganisms. The essential oils, n-hexane extracts and isolated compounds showed moderately activity, compared to standard antibiotics, inhibiting all tested bacteria except Pseudomonas aeruginosa. The most sensitive microorganism was Mycobacterium smegmatis, reaching MIC = 25 μg mL⁻¹. The results obtained suggest a potential application of these oils in preventing the human pathogenic and food spoilage due to microorganism’s growth. The essential oils and n-hexane extracts have greater RSC than polar extracts, probably due to the high contents in thymol, which demonstrated the highest activity in the DPPH assay. All studied origanum samples showed a large content in non-esterified 1-hexacosanol, C₂₆H₅₄O, accumulated mainly in bracts and flowers.     

Nucleolytic enzymes from the marine bacterium Cobetia amphilecti KMM 296 with antibiofilm activity and biopreservative effect on meat products

Cultivation of Pseudomonas aeruginosa (P. aeruginosa), Bacillus subtilis (B.subtilis), Salmonella enterica (S. enterica), and Staphylococcus aureus (S. aureus) isolated from meat products together with the marine bacterium Cobetia amphilecti KMM 296 (Cobetia marina) resulted in inhibition of their cell growth and complete degradation of biofilms of P. aeruginosa and B. subtilis. The degradation patterns of their mature biofilms treated with Cobetia amphilecti (C. amphilecti) extracellular nucleolytic enzymes revealed that the highly active alkaline phosphatase CmAP could be a significant antibiofilm factor. Moreover, CmAP possessed strong dose-dependent inhibition effect on de novo biofilm formation by bacterial cells regardless of the species. The concentration of CmAP for exhibition of maximal effect on microbial growth and biofilms was 1.1 μg/ml with activity of 2.5 units/ml that diminished total aerobic mesophilic and lactic acid counts in sausage shells by 3.5 log units for 5 days and 2.5 log units for 6 days, respectively. The stabilized antifungal effect continued the same period of storage. The nuclease-like enzymes CmEEP and CmNUC were species-independent and largely degraded biofilms at lowered pH. The biopreservative effect on meat products at low concentration and psychrophilicity of CmAP can be used for enzymatic cleaning of surfaces in food industry.     

Synthesis,characterization and comparative study of nano-Ag–TiO2 against Gram-positive and Gram-negative bacteria under fluorescent light

Currently, some of the major problems affecting the world are air pollution as well as microbial contamination. Every time we breathe, we are risking our lives by inhaling dangerous chemicals and biological contaminants that have found their way into the air. Therefore this work focuses on the antibacterial activity of Ag–TiO₂ to overcome the microbial contaminant and infectious disease. Ag–TiO₂ nanosolution were synthesized by sol–gel method and found to be an effective visible light driven photocatalyst. The nanosolutions were characterized by X-ray diffraction (XRD), transmittance electron microscopy (TEM), photoluminescence (PL) spectra, and X-ray photoelectron spectroscopy (XPS). At the concentration of 0.2–0.1 M, Ag–TiO₂ caused 100% inhibition of bacterial growth. The antibacterial efficacy of Ag–TiO₂ was evaluated with two kinds of bacteria; Gram-positive and Gram-negative. The colony count of Ag–TiO₂ against Gram-negative were evaluated with stain such as Escherichia coli, Pseudomonas aeruginosa and Shigella while for Gram-positive were investigated with Staphylococcus aureus, Bacillus subtilis, Bacillus cereus. Colony count results indicated that Ag–TiO₂ able to kill bacteria at the lowest concentration of 0.05 M that contains 0.06 mol % Ag. From the SEM and TEM observation, the survival of the Gram-positive was low and the decomposition was rapid as compared to Gram-negative bacteria.     

Antimicrobial potential and chemical composition of Mentha piperita oil in liquid and vapour phase against food spoiling microorganisms

Antimicrobial potential of Mentha piperita oil in liquid and vapour phase against different bacterial strains (Escherichia coli αDH5, Escherichia coli ATCC 25922, Pseudomonas aeruginosa, Pseudomonas fluorescens, Bacillus subtilis and Staphylococcus aureus), fungal strains (Penicillium digitatum, Aspergillus flavus, Aspergillus niger, Mucor spp, and Fusarium oxysporum) and yeasts (Candida albicans and Sacchromyces cerevisiae) was determined by agar dilution method, well diffusion method and disc volatilization method, respectively. Minimum inhibitory concentration (MIC) and Minimum bactericidal and fungicidal concentration (MBC/MFC) of M. piperita oil varied from 1.13 to 2.25 mg/ml and 2.25 to 9 mg/ml for bacterial strains, 1.13 to 2.25 mg/ml and 2.25 to 4.5 mg/ml for fungal strains and 1.13 mg/ml and 2.25 mg/ml for yeasts, respectively. Bacterial inhibition zone due to M. piperita oil (40 μl/well) varied from 13 mm (P. aeruginosa) to 22 mm (B. subtilis). Bacterial inhibition zone due to M. piperita oil (40 μl) vapour varied from 22 mm (P. fluorescens) to 35 mm (B. subtilis) while almost complete growth inhibition occurred in case of fungal strains. In the kill time assays, 100% reduction in viability of C. albicans and B. subtilis was found within 8 h exposure to M. piperita oil vapour. Significant morphological alterations due to the effect of M. piperita oil and oil vapour on B. Subtilis have also been observed by scanning electron microscope.Chemical constituents of the M. piperita essential oil and oil vapour have been identified by gas chromatography (GC), gas chromatography/mass spectrometry (GC–MS) and Solid phase micro extraction-gas chromatography mass spectrometry (SPME GC–MS), respectively.     

Modelling the effect of the temperature and carbon dioxide on the growth of spoilage bacteria in packed fish products

We have investigated the effect of storage temperature (0–20 °C) and carbon dioxide concentration (0–100% v/v, balance nitrogen) on the growth of Carnobacterium maltaromaticum, Serratia proteamaculans, Yersinia intermedia and Shewanella baltica, as well as on the growth of a mixed culture of the four species. These species were identified as the organisms responsible for spoilage in mackerel fillets packed under modified atmospheres in preliminary studies. The growth rates of all those groups were measured at several temperatures between 0 and 20 °C in cultures stored under air. Models describing the dependence of the maximum specific growth rate on temperature, CO₂ and O₂ were developed for each organism. C. maltaromaticum was the organism that showed the highest resistance to CO₂ and to the lack of O_2, while under aerobic condition at 0 °C. S. baltica showed the fastest growth rate. Model predictions were compared with observations on naturally contaminated horse mackerel fillets packed under modified atmospheres as well as inoculated with the bacteria strains used to generate the data for model development. These validation studies showed a good performance of models under constant and fluctuating temperature conditions. Models were implemented in a user-friendly computing tool called “Fishmap” (freely available at http://www.azti.es/en/fish-map-software.html). This program predicts the growth of spoilage bacteria in horse mackerel fillets stored at constant and fluctuating temperature conditions under modified atmospheres and under air.     

Chemical profiling with modeling differentiates Ictalurid catfish produced in fertilized and feeding ponds

Elemental analysis (Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, P, S, Se, and Zn) of fillets of channel catfish Ictalurus punctatus and hybrid catfish (♀ I. punctatus × ♂ blue catfish Ictalurus furcatus) from fertilized ponds and of hybrid catfish that received feed was performed using an inductively coupled plasma atomic emission spectrometry (ICP-AES). Fillets of samples of hybrid and channel catfish in fertilized ponds did not differ in composition for most of the elements analyzed. Multivariate statistical methods including principal component analysis (PCA), canonical discriminant analysis (CDA) and k-nearest-neighbor analysis were used to separate Ictalurid catfish to the two culture methods based on chemical composition. The three methods each demonstrated that fillets from fish that received feed could be differentiated from fillets of fish cultured in fertilized ponds. Fish from fertilized ponds rely on natural food organisms in the same manner as wild-caught fish. This study demonstrated the potential of chemical profiling combined with multivariate statistical methods for verifying method of production – aquaculture versus wild-caught.