Design of biopolymeric matrices entrapping bioprotective lactic acid bacteria to control Listeria monocytogenes growth: Comparison of alginate and alginate-caseinate matrices entrapping Lactococcus lactis subsp. lactis cells

In order to design biopolymeric matrices entrapping bioprotective lactic acid bacteria (LAB) to control undesirable microorganisms growth in foods, the performances of alginate and alginate-caseinate (an aqueous two-phase system) matrices entrapping Lactococcus lactis subsp. lactis LAB3 cells were compared. Since efficient matrices should preserve the culturability and the antimicrobial activity of entrapped LAB3 cells for prolonged periods, they were both monitored for 12 days storage at 30 °C. Maximal cell density (∼10⁹ CFU mL⁻¹) was reached after 24 h whatever the matrix type. Then, the LAB3 cells population decreased: 10⁷ and 10⁶ CFU mL⁻¹ were enumerated after 12 days in alginate-caseinate matrix and in alginate matrix, respectively. The anti-listerial activity assayed by an agar well method of LAB3 cells entrapped in alginate-caseinate matrices was also higher. LAB3 cells anti-listerial activity has been shown to be due to antimicrobial metabolites: hydrolysis by proteolytic enzymes of LAB3 cell-free culture supernatants (CFS) demonstrated the proteinaceous nature of at least a part of these metabolites. The higher antimicrobial activity of alginate-caseinate matrices might both result from the higher survival rate of bacterial cells and from a higher release of antimicrobial metabolites. To test this latter hypothesis, LAB3 CFS were incorporated in alginate and alginate-caseinate matrices and tested against Listeria innocua and Listeria monocytogenes. The anti-listerial activity of LAB3 CFS was higher in alginate-caseinate matrices indicating a better release of antimicrobial agents from this matrix. Alginate-caseinate matrices are thus better suited for LAB3 cells incorporation both for their survival and to promote the release of their antimicrobial metabolites.     

Lactic acid bacteria bioprotection applied to the malting process. Part I: Strain characterization and identification of antifungal compounds

Lactic acid bacteria (LAB) are of interest to cereal and beverage industry due to their contribution to the microbial safety and quality of fermented food/beverages. The main objectives of this study were to optimize the production of an antifungal cell-free-supernatant (cfs), based on lactic acid bacteria, using a wort-base substrate; and the subsequent identification of its active acid-base antifungal compounds. Two antifungal strains (Lactobacillus amylovorus DSM19280 and Lactobacillus reuteri R29) and a negative control strain (L. amylovorus DSM20552) were used. Barley based malt extract (wort) was produced and used as a fermentation substrate. Worts fermented with LAB were characterized in detail (total cell counts, pH, and total titratable acids (TTA) over time (0–120 h). A microtiter plate and an overlay agar based assay were used to evaluate the antifungal activity of the LAB cfs. Sugars, organic acids of the fermented and non-fermented wort (control) were analysed by HPLC. LAB antifungal metabolites were quantified using a QuEChERS method and an HPLC-UV/PDA system. Results show that wort produced from barley malt is a suitable substrate for LAB and dependent on the species and the fermentation time. The type of antifungal compounds can vary significantly. L. amylovorus DSM19280 cfs inhibited Fusarium culmorum spores at levels of 10⁴ spores.mL⁻¹, for 7 days, whereas L. reuteri R29 cfs inhibited up to 10⁵ spores.mL⁻¹ for the same time. Thirteen acid-base antifungal compounds were identified in L. reuteri R29 cfs and twelve in L. amylovorus DSM19280. Among them, phenyllactic, OH-phenylactic and benzoic acids were present at a significant concentration. This study demonstrates that the LAB wort-base cfs exhibits potent antifungal activity and is the ideal substrate for applications in a wide range of cereal products.     

Combined sustainable sanitising treatments to reduce Escherichia coli and Salmonella Enteritidis growth on fresh-cut kailan-hybrid broccoli

The effects of peroxyacetic acid (PA), neutral electrolysed water (NEW), ultraviolet C light (UV-C) and superatmospheric O₂ packaging (HO), single or combined, on the growth rate of Escherichia coli and S. Enteritidis inoculated onto fresh-cut kailan-hybrid broccoli were studied throughout 14 days of shelf life at 5 and 10 °C. As controls, unwashed, water-washed and NaClO-washed were used. PA and NEW showed a better sanitising effect than NaClO against both E. coli/S. Enteritidis with reductions of 2.2/2.7 and 2.6/2.6 log CFU g⁻¹, respectively. UV-C attained E. coli/S. Enteritidis decreases of 1.3–1.4/2.1–2.2 log CFU g⁻¹ compared to unwashed samples. The bacteriostatic effects of PA or NEW were improved when they were combined with UV-C, decreasing E. coli and S. Enteritidis counts by about 3 log CFU g⁻¹. After 14 days, PA and NEW-treated samples attained E. coli/S. Enteritidis reductions at 5 °C of 2.3/1.4 and about 1 log CFU g⁻¹, respectively. Storage of those samples at 10 °C masked that sanitising effect. At both storage temperatures, UV-C-treated samples registered lower E. coli and S. Enteritidis reductions (or higher increases for S. Enteritidis at 10 °C) regarding conventional NaClO-sanitized samples or other single treatments. However, PA, NEW or UV-C-treated samples under HO at both storage temperatures showed better bacterial control than individual treatments with the greatest effectiveness for UV-C + HO. Triple combination did not imply an enhanced benefit over double combinations. Conclusively, PA, NEW and UV-C seems to be effective emergent alternatives to NaClO to reduce initial E. coli and S. Enteritidis populations in fresh-cut kailan-hybrid broccoli. Storage at 5 or 10 °C under HO greatly controlled microbial growth.     

Influence of argon modified atmosphere packaging on the growth potential of strains of Listeria monocytogenes and Escherichia coli

Modified atmosphere packaging (MAP) based on carbon dioxide (CO₂) – nitrogen (N₂) gas mixtures has been applied to maintain the safety and quality of ready-to-eat (RTE) meat products. The use of argon (Ar) gas as a supplement to CO₂–N₂ mixtures or as substitute for N₂ is a current approach to enhance the effectiveness of MAP. As there is limited information on the effect of Ar MAP on the growth behaviour or the survival of pathogenic bacteria in RTE foods, the aim of the present study was to assess the influence of Ar in MAP on the growth of Listeria monocytogenes and Escherichia coli strains under different conditions. For this purpose, a CO₂–N₂ (20:80) atmosphere was compared with a CO₂–N₂–Ar (30:30:40) and CO₂–Ar (30:70) atmosphere based on the assessment of bacterial growth (δ) on a gelatin-agar medium and ham. Additionally, a shelf life monitoring study was performed to evaluate the effect of these treatments on the background microflora of ham. The findings suggest that under the CO₂–N₂ MAP the product matrices supported the growth (δ > 0.5 log CFU g⁻¹) of L. monocytogenes throughout an observation period of 21 days at 4 ± 2 °C. On the contrary, both MAP containing Ar were equally able to reduce the δ below 0.5 log CFU g⁻¹. In this regard it was irrelevant whether L. monocytogenes was inoculated in depth (per slice) or at the surface (top slice) of the ham. Regarding the influence of the different gas atmospheres on E. coli all gas mixtures applied had the capacity to reduce the δ of E. coli below −0.5 log CFU g⁻¹. Further, shelf-life extension could not be managed with the gas atmospheres considered.     

Inhibition of Staphylococcus aureus on beef by nisin-containing modified alginate films and beads

Nisin, a bacteriocin, was immobilized into palmitoylated alginate-based films or in activated alginate beads. Sterile beef muscle slices or ground beef were inoculated with Staphylococcus aureus at a level of 10⁴ CFU/g. Sliced beef was then coated with palmitoylated alginate-based films containing 0, 500 or 1000 IU/mL of nisin. Also, ground beef was mixed with 0, 500 or 1000 IU/mL of nisin covalently linked to activated alginate beads in order to evaluate the effect of nisin concentration on S. aureus level. The content of S. aureus in beef was determined during storage at 4 °C. Results demonstrated that after 7 days of storage, a reduction of 0.91 and 1.86 log CFU/cm² was observed on sliced beef covered with film containing 500 or 1000 IU/mL of nisin, respectively. After 14 days of storage, when nisin solution (500 or 1000 IU/g) was mixed with ground beef, 2.2 and 2.81 log CFU/g reductions of S. aureus counts were respectively observed. However, when nisin (500 or 1000 IU/g) was linked into activated alginate beads, 1.77 and 1.93 log CFU/g reductions of S. aureus counts were respectively observed (P ⩽ 0.05). These results suggest that sterile, hydrophobic and biodegradable films or beads incorporating various amounts of nisin could be used efficiently to control the growth of pathogens or microorganisms responsible of spoilage at the surface of round beef or other meat products.     

The efficacy of grape seed extract,citric acid and lactic acid on the inactivation of Vibrio parahaemolyticus in shucked oysters

The efficacy of grape seed extract (GE), citric acid (CA) or lactic acid (LA) on the inactivation of Vibrio parahaemolyticus in shucked oysters was studied. The minimum inhibitory concentration (MIC) of GE, CA or LA against V. parahaemolyticus in TSB-1% NaCl was also determined. The shucked oysters were artificially inoculated with V. parahaemolyticus, the inoculated shucked oysters (25 g) were then dipped in solution of GE (0.0, 10.0, 20.0, 50.0, 100, 200, 300 and 500 mg mL⁻¹), CA (0.0, 5.0, 10.0, 15.0, 20.0, 50.0, 100, 200 and 300 mg mL⁻¹) or LA (0.0, 1.0, 5.0, 10.0, 15.0, 20.0, 50.0, 100 and 150 mg mL⁻¹) for 10 min. The population of V. parahaemolyticus in shucked oysters was determined. The MICs of GE, CA or LA against V. parahaemolyticus were 10.0, 5.0 or 1.0 mg mL⁻¹, respectively. A 500, 300 or 150 mg mL⁻¹ GE, CA or LA solutions were needed to reduce the population of V. parahaemolyticus to below the detection level (1.0 log g⁻¹) in shucked oysters.     

Limited microbial growth in Atlantic salmon packed in a modified atmosphere

This study examined the dynamics of microbial growth in fresh chilled Atlantic salmon (Salmo salar) packed in a modified atmosphere. Atlantic salmon were harvested, handled, transported, and processed under optimal conditions to produce skinless fillet portions packed in pouches containing 96% CO₂ at gas: product ratios of greater than 5:1 (v/w) and stored for 38 days at less than 1 °C. Microbial analysis was conducted using psychrotrophic and mesophilic plate counts and DNA-based techniques. Results revealed initial microbial counts at day 0 of 10² CFU g⁻¹ and sequences from the genera Luteimonas, Pseudorhodoferax, Aequorivita, Gillisia, Gramella, Micrococcus, Acidovorax and Achromobacter. An extended lag phase was observed of 10 (psychrotrophic) or 15 (total) days with total plate count numbers reaching 10⁶ CFU g⁻¹ after 21 (psychrotrophic) and 25 days (total) and stabilising at 10⁸ CFU g⁻¹ after 31 days. At 31 days the microbial community was dominated by Pseudomonas spp. as determined by identification of isolates and sequencing of a 16S rRNA gene clone library. No Photobacterium spp., including the specific spoilage organism Photobacterium phosphoreum, were identified during the study.     

Essential oil composition and biological/pharmacological properties of Salmea scandens (L.) DC

Salmea scandens (L.) DC is an indigenous edible plant whose stem bark is traditionally used as food by people of Oaxaca, México. Proximate analysis of the edible stem bark revealed abundant amounts of fiber (43.67%) and protein (9.27%). GC and GC-MS analyses demonstrated that the essential oil from leaves contained high levels of germacrene D (47.1%) and elemol (15.3%), whereas that of the stem bark contained the alkylamides N-Isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamide isomers (39.7%). Levels of these compounds in the essential oil from both organs were in similar concentrations in all seasons except winter. The HPLC purified N-Isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamide isomers produced a non-competitive inhibition on porcine pancreatic lipase. The enzymatic assays with these compounds revealed a modification on V_max (0.0431–0.0533 mM min⁻¹) whereas the K_m value (0.880–0.881 mM) was not significantly changed. Essential oil from the stem bark showed a high anti-microbial activity against some phytopathogenic microorganisms. The MIC's in μg mL⁻¹ for Pseudomonas syringae pathovars were tabaci 56.1, tomato 91.2 and phaseolitica 196.4, for Clavibacter michiganensis 35.8 and Erwinia carotovora 48.1. The fungi Fusarium oxysporum and Phytophthora infestans had MIC's in μg mL⁻¹ of 3.3 and 2.4 respectively. Same essential oil was highly effective against larvae from Aedes aegypti (LC₅₀ = 0.3 μg mL⁻¹) and Anopheles albimanis (LC₅₀ = 2.5 μg mL⁻¹).     

Lactic acid bacteria in an alginate film inhibit Listeria monocytogenes growth on smoked salmon

Antimicrobial packaging with lactic acid bacteria incorporated into the film matrix is a novel approach for controlling the growth of food-borne pathogens in ready-to-eat food. The overall objective of this study was to assess the effect of two strains of lactic acid bacteria (LAB) and nisin trapped in an alginate matrix, on Listeria monocytogenes growth on vacuum packed cold-smoked salmon. A film was formulated containing two LAB strains and nisin (100 IU/mL). LAB viability and bacteriocin like substance production (BLS) were assessed using the plate antagonism technique. To check the film antagonistic activity, pieces of salmon (4.0 × 4.0 cm²), inoculated with L. monocytogenes at a final concentration of 10⁴ CFU/cm², were covered with film containing both LAB strains plus nisin and stored at 4 °C. L. monocytogenes colonies on OXA agar were counted after 0, 7, 14, 21 and 28 days to evaluate pathogen inhibition. All treatments led to effective diffusion of the BLS that inhibited L. monocytogenes for 20 days after film preparation, with inhibition zones of 5.7 cm² for film coupons of 8 mm in diameter. After 28 days, salmon pieces covered with the film without inhibitors showed an increase of 2.4 log cycles in L. monocytogenes growth. In contrast, films with either LAB strain or a combination of both strains and nisin had a bacteriostatic effect on the pathogen over a period of 28 days, which exceeds the industrial standard shelf life for smoked salmon. The results demonstrate that these films inhibit L. monocytogenes growth on salmon during refrigerated storage.     

Characterization and selection of Lactobacillus brevis starter for nitrite degradation of Chinese pickle

To improve the safety of Chinese pickles, lactic acid bacteria were isolated from traditional fermented foods to test for nitrite degradation during the pickling process. Lactobacillus brevis AR123 was screened out as a starter culture for pickle fermentation. L. brevis AR123 has a high tolerance to nitrite and salt. During pickle fermentation, the nitrite peak appeared from 12 to 24 h in the pickle juice and was delayed to 24–48 h in the pickles. In 6% salt, L. brevis AR123 and a commercial starter could rapidly lower the pH of the pickles, and the nitrite contents were 0.83 mg kg⁻¹ and 3.05 mg kg⁻¹, respectively, in pickles at 72 h. Meanwhile, no obvious nitrite peak was observed for the pickle inoculated with a mixed starter; it had a low nitrite level (0.88 mg kg⁻¹ at 72 h). However, the concentration of nitrite was as high as 17.92 mg kg⁻¹ in the spontaneous fermentation group. During pickle fermentation, Lactic acid bacteria (LAB) population increased significantly when salt concentration was 4%–8%, and sensory analysis shown that the L. brevis AR123 inoculated pickle exhibited better sensory evaluation results than spontaneous fermentation pickle. In conclusion, inoculation with L. brevis AR123 alone or combined with a commercial starter (mixed starter) is effective in removing nitrites and enhancing the sensory properties of pickle. LAB could accelerate degradation of nitrite significantly and shorten the fermentation time for pickle process.     

Antilisterial and physical properties of biopolymer films containing lactic acid bacteria

Novel biopolymer films were developed and used to control Listeria innocua in an artificially contaminated synthetized medium. Two hydrocolloids, sodium caseinate (NaCas) and methylcellulose (MC), and two bacteriocin-producing lactic acid bacteria (LAB), Lactobacillus acidophilus and Lactobacillus reuteri, were tested. Bioactive cultures were added directly to the film forming solution and films were obtained by casting. In order to study the impact of the incorporation of bacterial cells into the biopolymer matrix, the water vapour permeability, optical and mechanical properties of the dry films were evaluated. Furthermore, the survival of LAB and the antimicrobial potential of bioactive films against L. innocua were studied. Results showed that the use of lactic acid bacteria altered the film's physical properties. Films enriched with bacterial cells exhibit higher gloss and transparency whereas no significant modifications were observed in terms of tensile properties. These films were less-effective water vapour barriers, since a significant increase can be observed in the WVP values. As far as food safety is concerned, these films are an interesting, novel approach. In refrigeration conditions, these films permit a complete inhibition of L. innocua for a week. Viability of LAB was higher in sodium caseinate films, although bacteriocin production was greater in polysaccharide matrix. The best results were obtained for films made of methylcellulose, without differences between the two lactic acid bacteria tested.     

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.     

Development of an aptasensor for electrochemical detection of tetracycline

Developing the rapid, simple and sensitive biosensor system for tetracycline detection is very important in food safety. In this paper, we developed a label-free aptasensor for electrochemical detection of tetracycline. The reorganization of tetracycline binding aptamer was confirmed by Isothermal Titration Calorimetry, Kd = 5.18 × 10⁻⁵ mol L⁻¹. According to the electrochemical impendence spectroscopy (EIS) analysis, there was a linear relationship between the log concentration of tetracycline and the charge transfer resistance (ΔRet) from 5.0 to 5.0 × 10³ ng mL⁻¹ of the tetracycline conc. The detection limit was 1.0 ng mL⁻¹ within a detection time of 15 min. The average of assemble rate Q was at 82.4% with a differential batches' RSD of 4.6%. The current change of this aptasensor lies within at 8.5% after a storage of 15 days under 4 °C. The result aptasensor had shown a good reproducibility with an acceptable stability in tetracycline detection. The recoveries of TET in spiked milk samples were in the range of 90.0–95.7%.     

Development of an immunomagnetic separation method for efficient enrichment of Escherichia coli O157:H7

Immunomagnetic separation uses antibody-coated paramagnetic particles to selectively bind and purify the target organisms from a comprehensive range of complex food matrices. Aim of this study was to develop and optimize an immunomagnetic separation method based on monoclonal antibody for efficient isolation of Escherichia coli O157:H7 in food samples. The key parameters for preparing the immunomagnetic beads; the coupling rate between monoclonal antibody and magnetic beads, additive amount of immunomagnetic beads, and magnetic separation times were optimized with different concentrations of E. coli O157:H7. Under optimized conditions, the capture efficiency (CE) was greater than 98% against 10¹–10⁶ cells of E. coli O157:H7 with 0.05 mg immunomagnetic beads. The immunomagnetic beads exhibited high specific binding with E. coli O157:H7 strains (CE > 98%), and low binding with non-target bacteria (CE < 2%) except for S. aureus (CE = 23.6%). The capture efficiency of immunomagnetic beads against E. coli O157:H7 in ground beef and milk samples were 94.4% and 99.8%, respectively.     

A visual detection method for Salmonella Typhimurium based on aptamer recognition and nanogold labeling

A rapid, specific and visible detection method for Salmonella Typhimurium was developed based on the recognition of aptamers coupled with nanogold labeling and silver signal amplification. Briefly, biotinylated aptamer 1, which was specific to Salmonella Typhimurium, was immobilized onto the surface of microtiter plate-wells modified with streptavidin through the binding of biotin and streptavidin. Then, the target bacteria, Salmonella Typhimurium, and the aptamer 2-gold nanoparticle (aptamer 2-AuNPs) conjugates were incubated in the wells to form sandwich-type aptamer/bacteria/aptamer-AuNPs complexes. Under optimal conditions, the correlation between the concentration of Salmonella Typhimurium and the intensity of the signals was observed to be linear within the range of 10–10⁶ cfu mL⁻¹ (R² = 0.9913), and the detection limit of the proposed method was observed to be 7 cfu mL⁻¹ This developed method offers the potential for rapid, sensitive and visible detection of Salmonella Typhimurium in samples.     

Ultrasensitive immunoassays based on biotin–streptavidin amplified system for quantitative determination of family zearalenones

In this work, based on a newly obtained monoclonal antibody (MAb) against zearalenone (ZEN) and biotin–streptavidin system (BSAS) for signal amplification, two sensitive and rapid immunoassay formats including biotin–streptavidin amplified enzyme-linked immunosorbent assay (BA-ELISA) and biotin–streptavidin amplified fluorescence-linked immunosorbent assay (BA-FLISA), were developed for family zearalenones (ZENs) determination. And the limits of detection (LODs) of ZEN were 0.02 ng mL⁻¹ and 0.10 ng mL⁻¹ for BA-ELISA and BA-FLISA respectively. Using the BA-ELISA platform the half maximal inhibitory concentrations (IC₅₀) were 0.18 ng mL⁻¹ for ZEN, 0.39 ng mL⁻¹ for α-zearalenol (α-ZOL), 0.46 ng mL⁻¹ for β-zearalenol (β-ZOL), 0.30 ng mL⁻¹ for zearalanone (ZAN), 0.30 ng mL⁻¹ for α-zearalanol (α-ZAL), and 0.73 ng mL⁻¹ for β-zearalanol (β-ZAL). With the broad specificity, the developed immunoassays could be used as sensitive and valuable tools for detection of family ZENs. Additionally, the suitability of the proposed immunoassays for its application to corn flour and corn based baby food has also been investigated.     

Efficient separation and quantitative detection of Listeria monocytogenes based on screen-printed interdigitated electrode,urease and magnetic nanoparticles

Rapid screening of pathogenic bacteria contaminated foods is the key to prevent and control the outbreaks of foodborne illness. In this study, an impedance biosensor was developed using immunomagnetic nanoparticles for efficient separation and concentration of the Listeria monocytogenes cells, urease for amplifying the weak signal, and screen-printed interdigitated electrode for quantitative measurement of the impedance change of the catalysate. The magnetic nanoparticles (MNPs) coated by the monoclonal antibodies (MAbs) were used to separate the Listeria cells from the background and concentrate them in small volume of PBS. Then, the gold nanoparticles (GNPs) modified with the urease and the polyclonal antibodies (PAbs) were used to react with Listeria to form the MNP-Listeria-GNP sandwich complexes. The complexes were re-suspended with the urea to catalyze the hydrolysis of the urea into ammonium ions and carbonate ions, which were measured by the electrode. A new equivalent circuit was designed for simulation of the biosensor with a good fitting result. Under the optimized conditions, a linear relationship between the impedance changes and the concentrations of Listeria from 1.9 × 10³ to 1.9 × 10⁶ CFU/mL was obtained. The limit of detection of this biosensor was 1.6 × 10³ CFU/mL and the recovery of the spiked lettuce sample ranges from 94.7% to 103.8%. This proposed biosensor was developed at much lower cost than our previous studies and could be more applicable for in-field detection of foodborne pathogens.     

Improving the safety and quality of raw tuna fillets by X-ray irradiation

In this study, raw tuna fillet (25 g) samples were inoculated by immersing in 0.1% peptone water that contained 10⁸⁻⁹ CFU ml⁻¹ of a three-strain mixture of Salmonella enterica for 1 min. The samples were then air dried at 22 °C for 30 min (to allow bacterial attachment) in the biosafety cabinet and were packaged separately in sterilized bags prior to X-ray treatments (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 kGy). The surviving Salmonella populations on raw tuna fillets samples were evaluated using a nonselective medium (tryptic soy agar) for 6 h with xylose lysine desoxycholate (XLD) selective medium overlay. The plates were then incubated for an additional 18 h at 37 °C. Finally, the colonies were counted and the results were expressed as log CFU g⁻¹. Furthermore, un-inoculated tuna samples (25 g) were packaged separately in sterilized bags and exposed to the lowest and highest X-ray doses (0.0 and 6.0 kGy), then stored at 5 °C, 10 °C or 25 °C for 25, 15 or 5 days, respectively. On the testing-dates, samples were withdrawn and microflora (psychrotrophic and mesophilic) counts, quality [color (using Hunter colorimeter) and texture (using Instron machine)] were evaluated. The results indicated that more than a 6 log CFU reduction of Salmonella population being achieved with 0.6 kGy X-ray treatment. Furthermore, treatment with X-ray significantly reduced the initial inherent microbiota on raw tuna fillets and inherent levels were significantly (p < 0.05) lower than the control samples throughout the shelf-life storage at 5, 10 or 25 °C for 25, 15 or 5 days, respectively. There was a significant effect of X-ray treatment on tuna color after treatment (day 0). However, no significant differences (p > 0.05) in color or texture of control and treated samples were observed after (day 0). These results indicated that X-ray is a good preservative technology for seafood products intended to be consumed raw.     

Anti-Listeria innocua activity of silver functionalised textile prepared with plasma technology

Thin layers of silver particles (10–100 Å) were deposited by plasma technology on textiles mainly composed with cotton or polyester in order to obtain antimicrobial properties. The antimicrobial activity against a Listeria innocua strain (LRGIA 01) of these textiles was assessed following a protocol based on the ISO 20743-2005 standard. The number of cultivable bacteria on textiles was then monitored for 24 h. The microbial population after 24 h at 30 °C attained 10⁷ CFU g⁻¹ on control textiles while it did not exceed 10³ CFU g⁻¹ on plasma-treated textile. All plasma-treated with silver textiles were anti-Listeria (up to 7 log CFU g⁻¹ decimal reductions of L. innocua populations) and this observation was confirmed by scanning electron microscopy. These textiles could thus have potential applications in food-processing industry to control cross-contaminations by L. monocytogenes.     

Inactivation kinetics for Salmonella Enteritidis in potato omelet using microwave heating treatments

The aim of this study was to model the inactivation of Salmonella enterica serovar Enteritidis in pasteurized omelet internally inoculated at different microwave heating treatments (300 W; 450 W, 600 W and 800 W). Results indicated a non significant change in Salmonella populations during the first 30 s treatment at 300 W and 450 W, being log reductions lower than 0.5 log CFU g⁻¹. However, after 40 s treatment, log reductions had risen to 4.8 log CFU g⁻¹ at 800 W. Inactivation rates were higher at 600 W and 800 W (0.67 and 0.63 s⁻¹) than at 300 W and 450 W (<0.34 s⁻¹). The temperature-dependent parameters of a Weibull model obtained by Mattick, Legan, Humphrey & Peleg (2001) were evaluated. It was concluded that combinations characterized by a temperature equal or above 70 °C ensured a minimum 4 log reduction of Salmonella population (i.e. 300 W-80 s; 450 W-60 s or 600 W/800 W-40 s). These results may be of value in food service establishments, as target treatments for microwavable potato omelet portions.