Carvacrol nanoemulsion combined with acid electrolysed water to inactivate bacteria,yeast in vitro and native microflora on shredded cabbages

Carvacrol is an effective antimicrobial agent originated from essential oils, this natural antimicrobial agent has higher consumer acceptance compared to chemical agents. Due to the low solubility of carvacrol in water, carvacrol was delivered as a nanoemulsion. A carvacrol nanoemulsion contained 3.5% (w/w) oil phase (1% carvacrol and 2.5% corn oil, w/w) and 3.5% (w/w) Tween 80 was produced by ultrasonification at 10 min using 100% amplitude; the median particle size was 309 ± 19 nm. The nanoemulsion was shelf-life stable for 1 month without any significant changes in particle size. When applied against Escherichia coli ATCC 25922 and Pichia pastoris GS115 growth in nutrient broth, carvacrol nanoemulsion (0.5% w/w carvacrol) achieved 3 log reductions of microorganisms. When microorganisms were fixed and dried on stainless steel coupon surface, the carvacrol nanoemulsion treatment was more effective on E. coli than P. pastoris with about 5 and 0.3 log reduction of viable count, respectively. The native microflora on shredded cabbages was challenged by combining carvacrol nanoemulsion and acidic electrolysed water (AEW) that contained ≤ 4 mg/L free available chlorine (FAC). The treatment reduced about 0.5 log of aerobic mesophilic and psychrotropic bacteria counts and the antimicrobial activity of carvacrol nanoemulsion and AEW lasted up to 2 days. The results indicated that carvacrol nanoemulsion is promising in controlling the safety of fresh-cut vegetables.     

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.     

Inactivation of foodborne pathogens in powdered red pepper (Capsicum annuum L.) using combined UV-C irradiation and mild heat treatment

This study was performed to investigate the effectiveness of combined ultraviolet (UV-C) irradiation and mild heating as an alternative to conventional inactivation of foodborne pathogens, including Escherichia coli O157:H7 and Salmonella Typhimurium on powdered red pepper. A cocktail of three strains of E. coli O157:H7 ATCC 35150, ATCC 43889, ATCC 43890) and S. Typhimurium (ATCC 19585, ATCC 43971, DT 104) was inoculated onto powdered red pepper and then treated with UV-C irradiation and mild heat. A constant UV intensity (3.40 mW/cm²) of the emitting lamps was applied to samples for 5, and 10 min at 25, 35, 45, 55, and 65 °C, respectively. Also, quality change of powdered red pepper was measured in order to identify the efficiency of combined treatment. The reduction levels of E. coli O157:H7 and S. Typhimurium on powdered red pepper when treated with UV-C irradiation alone at 20.4 kJ/m² for 10 min was 0.22 and 0.29 log CFU/g, respectively. While, combined treatment with mild heating at 65 °C reduced the surviving numbers of each pathogens by 2.88 and 3.06 log CFU/g, respectively. Although the inactivation efficiency was influenced less by the UV-C radiation dose, the synergistic effect was observed with increasing temperature and UV-C radiation dose. CIE color value and extractable color value were not significantly (P > 0.05) different between non-treated and combination treated samples. The moisture and capsaicinoids contents showed significant (P < 0.05) differences when treated at 65 °C because of sample drying during heat treatment. Therefore, these results suggest that UV-C irradiation combined with mild heating can be utilized by the food industry in order to effectively inactivate E. coli O157:H7 and S. Typhimurium without incurring quality deterioration of powdered red pepper.     

Antimicrobial activity of nanoemulsions containing essential oils and high methoxyl pectin during long-term storage

The antimicrobial activity against Escherichia coli and Listeria innocua of nanoemulsions containing oregano, thyme, lemongrass or mandarin essential oils and high methoxyl pectin was assessed during a long-term storage period (56 days). On one hand, a higher antimicrobial activity was detected against E. coli compared to L. innocua regardless the EO type. Transmission Electron Microscopy (TEM) images showed a significant damage in the E. coli cells for both the cytoplasm and cytoplasmic membrane, led to cell death. The antimicrobial activity of the nanoemulsions was found to be strongly related to the EO type rather than to their droplet size. The lemongrass-pectin nanoemulsion had the smallest droplet size (11 ± 1 nm) and higher antimicrobial activity reaching 5.9 log reductions of the E. coli population. Nevertheless, the freshly made oregano, thyme and mandarin EO-pectin nanoemulsion led to 2.2, 2.1 or 1.9 E. coli log-reductions, respectively. However, the antimicrobial activity decreased significantly during storage regardless the EO type, which was related to the loss of volatile compounds over time according to our results. The current work provides valuable information in order to make progress in the use of nanoemulsions containing EOs as decontaminating agents in food products.     

Reduction of Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium populations on fresh-cut bell pepper using gaseous ozone

Bacterial contamination is the main cause of food poisoning which can lead to diarrhoea, abdominal cramp, vomiting as well as death. Bacterial contamination can potentially be controlled by application of gaseous ozone due to its antibacterial activity. Therefore, the objective of this study was to investigate the efficacy of gaseous ozone for reducing food-borne pathogens such as Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium on fresh-cut bell pepper. Efficacy of gaseous ozone to reduce bacterial populations was investigated in vitro and in vivo. Results showed that optimum effect of ozone on reducing bacterial populations was achieved with short term exposures of less than 6 h. Ozone reduced the bacterial population by disrupting bacterial cell structure, which lead to cellular death. Results also showed that bacterial cells have different resistance to ozone where ozone was more effective against L. monocytogenes, followed by E. coli O157 and Salmonella Typhimurium. Optimal reduction of the bacterial population on fresh-cut bell pepper was achieved with exposure to 9 ppm ozone for 6 h. This treatment reduced 2.89, 2.56 and 3.06 log of E. coli O157, Salmonella Typhimurium and L. monocytogenes populations, respectively. In conclusion, exposure to 9 ppm ozone for 6 h helps in reducing food-borne pathogen on fresh-cut bell pepper and has high potential to be an alternative sanitization treatment to reduce pathogen population on fruit.     

Effect of a pectin-based edible coating containing green tea powder on the quality of irradiated pork patty

Physicochemical, microbiological and sensorial qualities of cooked pork patty coated with pectin-based material containing green tea leaf extract powder were studied. Cooked pork patties were separated into three groups; uncoated control (C), coated with pectin-based materials (CP), and coated with pectin-based materials containing 0.5% green tea powder (CGP). The prepared patties were irradiated at 0 and 3 kGy using cobalt-60 gamma rays. Lipid oxidation, free radical scavenging effects, moisture content, total plate count, and sensory properties were evaluated during storage for 14 days at 10 °C. Lipid oxidation decreased (p ⩽ 0.05) and radical scavenging (p ⩽ 0.05) increased in the pork patties in CGP or CP relative to those of the controls when vacuum packaged. Coated patties contained higher moisture contents than the controls in both air- and vacuum packagings. The numbers of total aerobic bacteria were significantly reduced by the coating treatments as well as by irradiation. No difference were detected in sensory characteristics due to gamma irradiation or coating treatments.     

Combination of microbubbles with oxidizing sanitizers to eliminate Escherichia coli and Salmonella Typhimurium on Thai leafy vegetables

Microbubbles (MB) technology was applied in a washing process a few studies have been done with food materials, particularly to reduce the microbial contamination on leafy vegetables. This study determined the effectiveness of MB (Ø ∼ 50–70 μm) combined with three sanitizers acidic electrolyte water (AEO, 20 and 40 mg/L, ORP 910–1010 mV, pH 2.7–3.1), chlorine dioxide (ClO_2, 3 and 5 mg/L, ORP 550–680 mV, pH 7.1–7.5), and sodium hypochlorite (NaOCl, 40 and 80 mg/L, ORP 900–990 mV, pH 6.5–6.7) in order to inactivate Escherichia coli and Salmonella Typhimurium on artificially contaminated sweet basil (Ocimum basilicum Linh) and Thai mint (Mentha cordifolia Opiz.). Although air MB alone did not possess antimicrobial activity, washing with MB combined with the two oxidizing sanitizers (NaOCl and AEO) for 5 min resulted in an effective reduction in S. Typhimurium and E. coli on sweet basil and Thai mint with 2–3 log reductions (99.2–99.8%). Washing vegetables with MB and NaOCl at a concentration of free chlorine of 40 mg/L NaOCl or 20 mg/L AEO yielded the best results in killing S. Typhimurium with 1.21–1.90 and 0.67–2.25 log reductions, respectively. In addition, the reduction of E. coli and S. Typhimurium on sweet basil appeared to be higher than on Thai mint. Differences in surface roughness may assist the bubbles and sanitizers to detach bacterial cells and therefore increase the washing efficacy. Furthermore, applying sanitizers in washing solution was a powerful means of killing planktonic E. coli and S. Typhimurium in the wash water and preventing cross-contamination in the washing process.     

Efficacy of near neutral and alkaline pH electrolyzed oxidizing waters to control Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 from beef hides

In this study efficacy of near neutral and alkaline pH electrolyzed oxidizing waters to reduce aerobic plate counts (AC) and Enterobacteriaceae (EC) from uninoculated fresh cattle hides and Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 from inoculated hides were determined. Fresh hides were cut in to 15 by 20 cm pieces and subjected to a total of eight different treatment solutions; near neutral pH EO water (NEW-pH 6.5 at room temperature, 150 mg/L available chlorine), alkaline pH EO water (AEO-pH 11.6 at room temperature), hot alkaline pH EO water at 43 °C (HAEO-pH 11.60), alkaline pH EO water spray followed by 150 mg/L available chlorine containing near neutral pH EO water spray (A-NEW-both at room temperature), Blitz™ (PAA, pH 3.02 at room temperature), 5% lactic acid (LA, pH 2.04 at room temperature), deionized water (W) and no treatment (Control). For each treatment, 60 ml treatment solution was sprayed on hide using a hand held sprayer. Similar treatment protocol was employed to treat hide pieces inoculated with E. coli O157:H7 and S. Typhimurium DT 104. Five percent lactic acid spray treatment was found to be the most effective treatment and achieved 2.77, 2.74, 2.75 and 2.98 log CFU/cm² of AC, EC, E. coli O157:H7 and S. Typhimurium DT 104 reductions, respectively. All EO water treatments were equally effective in reducing all target microorganisms, except E. coli O157:H7. HAEO and A-NEW treatments yielded significant reduction of E. coli O157:H7 compared to other EO water treatments. These results indicate that various EO water treatments could become viable options to reduce pathogens on hide during slaughter.     

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.     

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.     

Radiation tolerance of Bacillus cereus pre-treated with carvacrol alone or in combination with nisin after exposure to single and multiple sub-lethal radiation treatment

Currently little information exists on the response of Bacillus cereus after repetitive exposure to combined mild treatments involving antimicrobials and gamma irradiation. Therefore, the aim of this present study was to evaluate the radiation stress on growth and physiology of B. cereus LSPQ 2872 vegetative cells at stationary phase, following exposure to single and repetitive sub-lethal γ-radiation treatment at 1 kGy simultaneously with carvacrol alone or combined with nisin at sub-inhibitory concentrations. Results indicated that the combination of carvacrol and nisin significantly enhance the radiation sensitivity of B. cereus since lower D₁₀ values were recorded after both single and repetitive irradiation treatments. Flow cytometric analysis of radiation-stressed B. cereus cells following repetitive treatment revealed the heterogenic behaviour of the bacterium leading to the induction of a radiation tolerance response. When compared to carvacrol alone, the combination of carvacrol and nisin developed also increased radioresistance if repetitively processed with γ-radiation at 1 kGy, since the decrease percentage of dead cells was accompanied by an increase in the number of injured cells. However, good agreement was not found between classical plate counting (log cfu reductions) and flow cytometry method. For both antimicrobials, the increase of radioresistance after repetitive mild treatment was not accompanied by augmentations of lag phase or growth rate. The structural changes of the outer membranes were assessed by TEM analysis and results revealed that radioresistance might be related to changes in the cell wall.     

Inactivation by 405 ± 5 nm light emitting diode on Escherichia coli O157:H7, Salmonella Typhimurium,and Shigella sonnei under refrigerated condition might be due to the loss of membrane integrity

The objective of this study was to evaluate the antibacterial effect of 405 ± 5 nm light emitting diode (LED) on Escherichia coli O157:H7, Salmonella Typhimurium and Shigella sonnei. Its antibacterial mechanism was also investigated by determining the permeability of bacterial membrane and DNA degradation. Bacterial strains in phosphate-buffered saline were exposed to 405 ± 5 nm LED to a final dose of 486 J/cm² (7.5 h) at 4 °C. The inactivation curves were fitted by Weibull model to compare the sensitivities of pathogens to the LED illumination by calculating the decimal reduction times (t_R). The bacterial sensitivity to bile salts and NaCl by LED illumination was also determined. LIVE/DEAD^® BacLight™ staining as well as comet assay and DNA ladder analysis were carried out to determine the bacterial membrane integrity and DNA degradation, respectively. Results showed that LED illumination inactivated 1.0, 2.0, and 0.8 log CFU/ml for E. coli O157:H7, S. Typhimurium, and S. sonnei for 7.5 h, respectively. The comparison of t_R values demonstrated that S. Typhimurium was found to be the most (P < 0.05) susceptible strain to LED illumination. Regardless of the bacterial strain, the sensitivity of illuminated bacterial cells to bile salts and NaCl considerably increased compared to non-illuminated controls. Furthermore, LIVE/DEAD^® assay clearly showed that LED illumination resulted in loss of bacterial membrane permeability. On the other hand, no DNA degradation was observed by both comet assay and DNA ladder analysis. Therefore, these results suggest that the antibacterial effect of 405 ± 5 nm LED might be partly attributed to the physical damage to bacterial cell membrane. This study proposes that 405 ± 5 nm LED under refrigerated conditions may be effective to control the pathogens on foods.     

Synergetic antibacterial efficacy of cold nitrogen plasma and clove oil against Escherichia coli O157:H7 biofilms on lettuce

This study aims to evaluate the antimicrobial effects of cold nitrogen plasma (CNP) and clove oil against Escherichia coli O157:H7 (E. coli O157:H7) biofilm on lettuce. Both clove oil (1 mg/mL, 2 mg/mL and 4 mg/mL) and CNP (400–600 W) displayed significant eradication effect on E. coli O157:H7 biofilms in vitro (p < 0.001). Subsequently, the antibiofilm effect of combined treatment was studied as well. Compared with the respective treatment, combined treatment exhibited remarkable synergistic effect on eradicating E. coli O157:H7 biofilms. The confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) had also visually testified that the antibacterial effects of clove oil on E. coli O157:H7 biofilms (in vitro and on lettuce) were enhanced by CNP at 400 W for short treatment duration. The results of sensory evaluation indicated that combined treatment has mild negative effect on lettuce quality. Moreover, the synergetic antibacterial mechanism of clove oil and CNP against E. coli O157:H7 was concluded as that they could damage the bacterial cell wall and the outer membrane, leading to leakage of cellular components, such as nucleic acid and ATP.     

Persistence of Escherichia coli following irrigation of strawberry grown under four production systems: Field experiment

A two-year field experiment was conducted in order to evaluate the persistence of generic Escherichia coli in strawberry after irrigation with naturally E. coli-contaminated surface water. Sixteen experimental plots representing actual field conditions were set, including two methods of irrigation (overhead and subsurface drip) and two mulch types (straw and plastic). Two irrigations were performed each year with water having an E. coli content varying between 460 and 2242 CFU per 100 ml. Strawberries were harvested before irrigation and 1, 4 and 24 h following irrigation. E. coli counts could not be determined in any of the 256 strawberry samples. Enrichment procedure revealed more positive samples under straw mulch (6.4%) compared to plastic mulch (4.3%), but this difference was not statistically significant (P = 0.3991). Higher strawberry contamination was also observed in overhead irrigation treatments (8.6%) compared to drip irrigation (2.1%) (P = 0.0674). The risk to detect E. coli in overhead-irrigated strawberries was 4.5-fold higher than in strawberries under drip irrigation. Four hours following irrigation, the risk to detect E. coli in fruits was 4.0-fold lower than the risk observed 1 h after irrigation. Increasing the delay to 24 h led to a 7.4-fold lower risk. In actual conditions that may be encountered in strawberry productions, this study showed a limited persistence of E. coli in strawberries following irrigation.     

Antibacterial activity and mechanism of cinnamon essential oil against Escherichia coli and Staphylococcus aureus

Cinnamon essential oil (EO) exhibited effective antibacterial activity against foodborne spoilage and pathogenic bacteria in model systems using Escherichia coli and Staphylococcus. The minimum inhibition concentration (MIC) of cinnamon EO was similar for both bacteria (1.0 mg/ml) while the minimum bactericide concentration (MBC) were 4.0 mg/ml and 2.0 mg/ml for E. coli and Staphylococcus aureus. GC–MS analysis confirmed that cinnamaldehyde was the major constituent in cinnamon EO (92.40%). Much effort was focused on elucidating the mechanism of antibacterial action of cinnamon EO against E. coli and S. aureus by observing the changes of cell microstructure using scanning electron microscope, determination of cell permeability, membrane integrity and membrane potential. After adding cinnamon EO at MIC level, there were obvious changes in the morphology of bacteria cells indicating cell damage. When cinnamon EO were added at MBC levels, the cells were destroyed. Cinnamon EO led to leakage of small electrolytes, causing rapid increase in the electric conductivity of samples at the first few hours. The values for E. coli and S. aureus reached 60% and 79.4% respectively at 7 h. Moreover, the concentration of proteins and nucleic acids in cell suspension also rose with increased cinnamon EO. Bacterial metabolic activity was decreased 3–5 folds as reflected by the results of membrane potential. Overall, S. aureus was more susceptible to cinnamon EO than E. coli.     

Decontamination of incoming beef trimmings with hot lactic acid solution to improve microbial safety of resulting dry fermented sausages – A pilot study

In the study, beef trimmings intended for sausage production were subjected to different decontamination treatments based on lactic acid-hot water combination, with aim to eliminate or reduce foodborne pathogens Escherichia coli O157, Salmonella Typhimurium and Listeria monocytogenes in resultant dry, fermented sausages. In finished sausages, produced from untreated trimmings, “natural” reductions of inoculated E. coli O157 and Salmonella Typhimurium were on average 1.9 logs, L. monocytogenes count remained unchanged, and no detectable concentrations of biogenic amines were found. The same type of sausages were also produced by using beef trimmings which was pathogen-inoculated and then decontaminated by: hot, 4% lactic acid in water solution (90 °C for 10 s; treatment HLA1); or hot, 4% lactic acid in water solution (85 °C for 20 s; treatment HLA2), or hot, 4% lactic acid in water solution (80 °C for 30 s; treatment HLA3). The use of HLA-decontaminated beef trimmings resulted in total E. coli O157 reductions of at least 3.9 logs and in total Salmonella Typhimurium reductions of at least 3.6 logs, whilst biogenic amines were not detected in finished sausages. The overall sensorial acceptability of finished sausages produced with HLA-decontaminated beef trimmings was somewhat diminished. Further work is required to optimise the HLA-based incoming beef treatments.     

Use of gamma irradiation for inactivation of pathogens inoculated into Kimbab,steamed rice rolled by dried laver

The effect of gamma irradiation for inactivating the pathogens inoculated into the ready-to-eat Kimbab, steamed rice rolled by dried laver, was investigated. The pathogens used were Salmonella Typhimurium, Escherichia coli, Staphylococcus aureus and Listeria ivanovii which are important for public health. The growth of four test organisms inoculated (about 10⁶–10⁷ CFU/g) into the Kimbab were sustained by an irradiation treatment during 24 h of storage regardless of the temperature at 10, 20 and 30 °C. Four pathogen inoculated into Kimbab decreased 2–3 log CFU/g by 1 kGy treatment and was not detected after 3 kGy. The D₁₀ value of pathogens inoculated into the Kimbab were 0.31–0.44 kGy among the four organisms. This study indicated that a low dose irradiation can maintain microbial safety for ready-to-eat Kimbab, steamed rice rolled by dried laver.     

Effects of blackberry juice on growth inhibition of foodborne pathogens and growth promotion of Lactobacillus

Berries such as blueberry, blackberry and raspberry possess several biological activities including antimicrobial and nutritional effects. In this study, the antimicrobial activities of blackberry (Rubus fruticosus) juice against foodborne pathogens including Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli O157:H7 were investigated. Inhibition of growth of these foodborne pathogens was measured in broth (Luria–Bertani broth for E. coli O157:H7 and S. Typhimurium, and brain heart infusion broth for L. monocytogenes), skim milk and whole milk supplemented with 10% blackberry juice at different time points (0, 24, 48 and 72 h). The effects of blackberry juice on the growth of Lactobacillus casei, Lactobacillus plantarum and Lactobacillus rhamnosus were also investigated in Man–Rogosa–Sharpe (MRS) broth and skim and whole milk supplemented with blackberry juice. The growth of L. monocytogenes, S. Typhimurium and E. coli O157:H7 were significantly inhibited by blackberry juice by 1–3 logs in both milk and broth. We also observed that the growths of Lactobacillus strains were significantly stimulated (1–4 logs CFU/mL) by blackberry juice in both milk and MRS broth. These data clearly demonstrate that diluted blackberry juice can be used as a preservative in food processing and a preventive in foodborne infections as a natural antimicrobial.     

Combined effect of carvacrol and citral on the growth of Listeria monocytogenes and Listeria innocua and on the occurrence of damaged cells

The aim of this study was to evaluate the growth kinetics of Listeria innocua Serovar 6a (CECT 910) and Listeria monocytogenes Serovar 4b (CECT 4032) exposed to combinations of carvacrol and citral (0.0 μL/mL (control), 0.050 μL/mL of carvacrol and 0.075 μL/mL of citral, 0.050 μL/mL of carvacrol and 0.125 μL/mL of citral, 0.085 μL/mL of carvacrol and 0.075 μL/mL of citral, and 0.085 μL/mL of carvacrol and 0.125 μL/mL of citral), with two initial inoculum concentrations, and also the occurrence of sublethal damage in these cell populations. The terpene combinations exhibited antibacterial activity against L. innocua and L. monocytogenes and the effects were dependent on the concentration of terpenes present in the culture medium (p ≤ 0.05). When terpene-treated L. innocua and L. monocytogenes were incubated in TSB, significant differences in lag phase and growth rate were observed between low and high inoculum concentrations (p ≤ 0.05), indicating that the inoculum level should be taken into account in modeling studies. When bacterial cells were exposed to terpenes the proportion of sublethally injured cells increased with the increase in the terpene dose (p ≤ 0.05). In conclusion, all of these results show that carvacrol and citral can be used in combination at 25% of the MIC in order to control Listeria growth.     

Anti-microbial effectiveness of relative humidity-controlled carvacrol release from wheat gluten/montmorillonite coated papers

Wheat gluten coated papers containing carvacrol (15wt%) as anti-microbial agent and montmorillonite (0-7wt%) as filler were investigated as anti-microbial controlled delivery systems. The carvacrol losses were followed during the coating process and storage time at 30∞C under controlled RH from 40 to 100% RH. Increasing MMT content limited carvacrol losses during the coating process. A mathematical model based on Fick’s second law was used to determine the apparent diffusivities of carvacrol from experimental data of kinetic release at 30∞C and controlled RH. Diffusivity values varied from 0.143 × 10^?14 m²/s (0wt% MMT, 40% RH) to 6.010 × 10^?14 m²/s (5wt% MMT, 100%RH) depending on both MMT% and RH. The carvacrol diffusivities increased with increasing RH, and the presence of a high amount of MMT (≥5wt%) accentuated the RH-induced effect. Specific aggregated structure was evidenced by SEM and TEM in the presence of carvacrol and 5wt% MMT creating a preferential pathway for carvacrol diffusion. The anti-microbial efficiency of the MMT-WG-coated papers toward Escherichia Coli was assessed and showed that the anti-microbial effect was related to the carvacrol diffusivity. The diffusivity coefficients were utilized to optimize the packaging characteristics required to develop an efficient anti-microbial system and were finally validated against Botrytis cinerea.