Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

Effectiveness of multiple chemical sanitizers on the reduction of Salmonella spp. and Escherichia coli O157:H7 on spinach was compared. Fresh spinach (Spinacia oleracea) was inoculated with a bacterial suspension containing multiple strains of rifampin-resistant Salmonella and E. coli O157:H7. Inoculated spinach leaves were treated with a water wash or water wash followed by 2% L-lactic acid at 55 °C, peroxyacetic acid (80 mg/L), calcium hypochlorite (200 mg/L), ozonated water (mg/L) or ClO₂ gas (1.2 or 2.1 mg/L). The l-lactic acid produced a 2.7 log CFU/g reduction for E. coli O157:H7 and a 2.3 log CFU/g reduction for Salmonella, statistically significant compared to water wash alone (P < 0.05), which resulted in a reduction of 0.7 log CFU/g for both pathogens. These findings indicate that 2% l-lactic acid at 55 °C may be an effective treatment for reducing pathogens on spinach leaves.     

Decontamination of Salmonella enterica Typhimurium on green onions using a new formula of sanitizer washing and pulsed UV light (PL)

Pathogenic bacteria such as Salmonella and Shigella flexneri have been linked to green onion contamination. This study was conducted to evaluate decontamination of Salmonella Typhimurium using a new formula of sanitizer washing (0.4 mg/mL thymol and five new formula sanitizers including 300 ppm H₂O₂ + 4% SDS, 2 mg/mL citric acid + 4% SDS, 0.2 mg/mL thymol + 4% SDS, 0.2 mg/mL thymol + 2 mg/mL citric acid and 0.2 mg/mL thymol + 2 mg/mL acetic acid), pulsed UV light (PL) as well as synergy between the sanitizer wash and PL. New formula sanitizers based on decontamination efficacy of single washing solutions (organic acids, hydrogen peroxide (H₂O₂), essential oil or surfactant) were applied to decontaminate spot inoculated green onions. PL, the novel technique, alone has been applied to inactivate Salmonella on both dip and spot inoculated green onions. Salmonella inactivation of PL–new formula sanitizer combinations on dip inoculated green onions was investigated for their potential synergy. As a result, for spot inoculated green onions, 0.4 mg/mL thymol individually and the five new formula sanitizers all achieved higher log reduction of Salmonella (4.5–5.3 log 10 CFU/g reduction) than the 200 ppm chlorine washing. These new formulas of sanitizer would be potential alternatives to chlorine. The 5 s dry PL (4.6 log 10 CFU/g) or 60 s wet PL treatment (3.6 log 10 CFU/g) was better or comparable as chlorine washing. The sanitizer combinations did not provide significantly higher log reduction than PL, and PL has the potential of being used in the green onion industry for decontamination purpose. For dip inoculated green onions, none of our treatment provided > 0.8 log 10 CFU/g (0.6–0.8 log 10 CFU/g) reduction of Salmonella. As a result, the PL–new formula sanitizer combinations had no or minimal synergy to inactivate Salmonella dip inoculated on green onions.     

Inactivation of bacterial pathogens on lettuce,sprouts, and spinach using hurdle technology

Effects of chemical treatment using slightly acidic electrolyzed water (SAEW), fumaric acid (FA), or calcium oxide (CaO) and physical treatment using ultrasonication (US), micro-bubbles (MB), or ultraviolet (UV) to inactivate bacterial pathogens Listeria monocytogenes, Escherichia coli O157:H7, Staphylococcus aureus, and Salmonella spp. on lettuce, spinach, and sprouts were determined. Fresh produce inoculated with bacterial pathogens (~ 9 log CFU/mL) was immersed in distilled water (DW), SAEW, FA (0.5%), or CaO (0.2%) alone or in combination at 23 ± 2 °C for 3 min followed by treatment with US, MB for 3 min, or UV for 10 min. Effects of combined treatment on shelf-life of lettuce at 4 °C and 23 ± 2 °C were also determined in this study. Results revealed that the use of a combination of CaO + SAEW + FA + US exhibited significant reduction (p < 0.05) for bacterial pathogen on fresh produce compared to individual treatment or other combinations. CaO + SAEW + FA + US treatment exhibited highest reduction of E. coli O157:H7, S. aureus, L. monocytogenes and Salmonella spp. by 4.7, 4.9, 4.84 and 5.08 log CFU/g, respectively on lettuce as compared to spinach and sprouts. Microbial count reducing capability for combined treatment methods were ranked in the following order: SAEW + FA < CaO + SAEW + FA < CaO + SAEW + FA + US. However, introduction of US to CaO + SAEW + FA treatment resulted in little detrimental effect on the overall quality of lettuce. Moreover, CaO + SAEW + FA treatment effectively enhanced the shelf-life of lettuce stored at 4 °C and 23 ± 2 °C by about 6 days and 3 days, respectively as compared to control (DW treatment), with longer lag time (23.11 h on lettuce) for naturally occurring bacteria on fresh produce. These findings suggest that significant synergistic benefit could be obtained from combined sanitizer treatment to eliminate bacterial pathogens from fresh produce.     

Effect of temperature,pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

The aim of this investigation is to evaluate the concurrent influence of temperature (4–50 °C), pH (3.5–7.0), and the presence of nisin (up to 200 μg/mL) on the inactivation of two PEF-resistant Gram-negative, pathogenic bacteria, Salmonella Typhimurium STCC 878 and Escherichia coli O157:H7, using a PEF treatment of 30 kV/cm and 99 μs. A response surface model using a central composite design was developed for the purpose of understanding the individual effects and interactions of these factors.The models showed that temperature was the factor with the greatest influence on the PEF inactivation in the two strains investigated. Increasing the treatment temperature from 4 to 50 °C increased the lethality of PEF up to at least 4 Log₁₀ reductions for both microorganisms at all pH levels investigated. PEF lethality varied with the square of the pH observing the highest microbial PEF sensitivity at pH 5.25 at all temperatures. The addition of nisin to the treatment medium did not influence the PEF lethality independently of the temperature.PEF induced 1.0–1.5 Log₁₀ cycles of damaged cells at pH 3.5 for Salmonella Typhimurium STCC 878 and at pH 5.25 for E. coli O157:H7, independently of the temperature or the presence of nisin in the treatment medium.The application of PEF at 50 °C permitted the achievement of 5 Log₁₀ reductions of Salmonella Typhimurium STCC 878 and E. coli O157:H7 in a range of pH from 4.2 to 6.7 and from 4.5 to 6.0, respectively. Therefore, the application of PEF at moderate temperatures has great potential for achieving effective control of Gram-negative pathogenic microorganisms in the range of pH found in most foods.     

Fat contributes to the buffering capacity of chicken skin and meat but enhances the vulnerability of attached Salmonella cells to acetic acid treatment

Chicken skin and chicken meat display different buffering effects which may impact the survival of Salmonella attached to them when treated with acids. This study investigated the role that differences in fat composition of chicken skin and meat play in their buffering capacity. The survival of Salmonella attached to chicken skin and meat in the presence of fat, and treated with acetic acid was also investigated. Fat was extracted from chicken skin and meat and the buffering capacities of chicken skin, meat, extracted fat and their respective remnants were determined. Two strains of Salmonella Typhimurium and two strains of S. Enteritidis were attached independently to each of the chicken component listed above and enumerated before and after treatment with 0.3 M acetic acid. Chicken skin has a higher fat content as compared to chicken meat. Skin (13 mmol H⁺/(pH1 kg)) had a stronger buffering capacity (p < 0.05) than the extracted fat alone and skin remnants alone (7.0 mmol H⁺/(pH 1 kg) and 6.9 mmol H⁺/(pH 1 kg) respectively). From an initial inoculum (~ 9 log CFU/g), Salmonella cells attached better (p < 0.05) to chicken meat (~ 8 log CFU/g) and chicken skin (~ 7 log CFU/g) than extracted fat (~ 1.5 log CFU/g). Skin remnants without fat were better (p < 0.05) at protecting attached Salmonella than other chicken components. For example S. Typhimurium ATCC 33062 decreased ~ 1 log CFU/g (p < 0.05) on skin remnants after acetic acid treatment while its viable counts on other components decreased from ~ 1.5 to 7 log CFU/g (p < 0.05). We suggest that the fat content present in the skin may enhance the vulnerability of attached cells to acetic acid.     

Examination of the internalization of Salmonella serovar Typhimurium in peanut,Arachis hypogaea,using immunocytochemical techniques

A variety of products of plant origin, such as tomatoes, melons, peppers, and peanuts, have been implicated in Salmonella spp. associated outbreaks in recent years. Although these bacteria have been found to internalize within some plants associated with foodborne-related outbreaks, the internalization in peanut plants has not been examined to date. To investigate internalization and where the bacteria localize within the plant, intact peanut seeds were contaminated with Salmonella serovar Typhimurium expressing green fluorescent protein (GFP) for 30 min and immunocytochemical techniques were used to localize the bacterium within the stem tissue of 16 day-old peanut plants. An average of 13.6 bacteria/mm³ were localized within the sampled tissue. The bacteria were found to be associated with every major tissue (cortical, vascular, epidermal, and pith) and corresponding cell type. The cortical cells located to the outside of the vascular bundles contained the majority of the Salmonella cells (72.4%). Additional growth experiments demonstrated peanut seedlings could support the reproduction of Salmonella to high levels (10⁹ CFU/plant) after 2 days following seed contamination. Together these results show that Salmonella Typhimurium can internalize within many different plant tissue types after a brief seed contamination event and that the bacteria are able to grow and persist within the plant.     

Survival of probiotic bacteria in a whey cheese vector submitted to environmental conditions prevailing in the gastrointestinal tract

Various foods may be used to deliver probiotic bacteria into the gastrointestinal tract; one such example is Requeijão, a Portuguese whey cheese. Survival and stability of Bifidobacterium animalis strains BLC-1, Bb-12, and Bo, Lactobacillus acidophilus strains LAC-1 and Ki, L. paracasei ssp. paracasei strain LCS-1 and L. brevis strain LMG 6906 inoculated into Requeijão, when exposed to simulated gastrointestinal tract conditions, were assessed. Homogenates of inoculated whey cheese in 0.85% (w/v) sterile saline water were exposed to a solution of hydrochloric acid (pH 2.5–3.0) and pepsin (1000 units mL^–1) at 37 °C, and then to 0.3% (w/v) bile salts after 60 or 120 min of acid exposure. All bacterial strains retained their initial viable cell numbers. Bifidobacterium animalis strains Bb-12 and Bo, and L. brevis strain LMG 6906 exhibited the highest viable cell numbers when exposed to bile salts, whereas the other strains had variable death rates.     

Evaluation of pea protein–polysaccharide matrices for encapsulation of acid-sensitive bacteria

Protein–polysaccharide capsules containing Bifidobacterium adolescentis were produced and tested in a series of in vitro survival experiments to evaluate capsule protection of the bacterium to simulated stomach conditions, as well as their ability to release the encapsulated bacteria under conditions similar to those found in the lower gut. A protein fraction isolated from peas (pea protein isolate: PPI; 2.0%; w/v) was mixed with each of three different polysaccharides (0.5% (w/v) of either sodium alginate, iota-carrageenan and gellan gum) to produce capsules ranging in size from 2 to 3 mm diameter. All capsule formulations provided significant protection for cells exposed to synthetic stomach juice at 37 °C relative to non-encapsulated bacteria. In addition, PPI-alginate and PPI-iota-carrageenan capsules were found to dissolve in simulated intestinal fluid at 37 °C, releasing 70–79% of their bacteria “payload” within 3 h, with higher cell numbers being released from the freeze-dried capsules. PPI-gellan gum capsules did not dissolve to the same extent and the number of released cells was ~ 26–30% lower. Following a temporal rat feeding study with the test bacterium encapsulated in PPI-alginate, B. adolescentis-specific PCR and qPCR analyses confirmed the presence of DNA from this species in rat feces, but only during the period of capsule intake.     

Probiotic bacteria induced improvement of the mucosal integrity of enterocyte-like Caco-2 cells after exposure to Salmonella enteritidis 857

Probiotics protect the intestinal epithelium. Whether their protection against Salmonella is mediated via stabilizing the barrier integrity was examined here. The intestinal barrier integrity was assessed by measuring the trans-epithelial electrical resistance (TER) of Caco-2 cell monolayer. Cells were exposed for 1 h to Lactobacillus casei W56, Lactobacillus salivarius W24, Lactobacillus acidophilus W70, Lactococcus lactis W58, Bifidobacterium infantis W52 or Bifidobacterium bifidum W23 at 200 bacteria/cell or to Salmonella enteritidis 857 at 1–200 bacteria/cell or to a combination of either of the probiotic and Salmonella both at 200 bacteria/cell. Heat shock protein (Hsp) 70 was assessed by Western blotting. Probiotics induced a significant increase while Salmonella decreased the TER. The latter was attenuated by probiotics but without full recovery. In addition, probiotics induced over-expression of Hsp70. It may be concluded that probiotics stabilise the intestinal integrity and impede Salmonella infection via, at least in part, production of Hsp70.     

Volatile components and antibacterial effects of pine needle (Pinus densiflora S. and Z.) extracts

The antibacterial effects of the volatile components extracted from Pinus densiflora S. and Z., by simultaneous steam distillation and solvent extraction (SDE), were examined on six foodborne bacteria using Bioscreen C (a computer-controlled shake–incubator–reader). The SDE extracts of P. densiflora obtained after 1.5 or 2.0 h at pH 3.6 exhibited a strong growth inhibitory effect on Escherichia coli O157:H7 and their overall antibacterial activities against the various bacteria tested tended to increase with increased extraction time and with a lower extraction pH. The major volatile components of the SDE extracts obtained at pH 3.6 and 1.5 h, as determined by gas chromatography, were α-ocimene (29.3%), sabinene (10.9%), β-myrcene (9.6%), β-caryophyllene (8.0%), β-cadinene (7.3%), α-terpinolene (4.9%), 2-hexanal (4.5%), and β-pinene (4.3%). The addition of 8% or 10% (v/v) of the SDE extracts to culture broth completely inhibited the growths of Bacillus cereus, Salmonella Typhimurium, and Staphylococcus aureus. The intracellular adenosine triphosphate (ATP) concentration of S. Typhimurium treated with P. densiflora extract reduced to 0.165 μm from 0.595 μm, whereas the ATP concentration in culture supernatants was increased to 0.469 μm form 0.065 μm.     

Application of bacteriophages during depuration reduces the load of Salmonella Typhimurium in cockles

As bivalve molluscs are filter feeder, often consumed raw or lightly cooked and are frequently cultivated in contaminated waters, they are implicated in food-borne disease transmission to human. The present study investigated the potential application of bacteriophage (or phage) phSE-2, phage phSE-5 and phage cocktail phSE-2/phSE-5 to decrease the concentration of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) during the depuration of natural and artificially contaminated cockles (Cerastoderma edule). Cockles were artificially infected with 10⁵ and 10⁶ colony-forming units (CFU)/mL of S. Typhimurium in static seawater and infected group were treated with phages at four different MOI values: 0.1, 1, 10 and 100. Depuration in static seawater at multiplicity of infection (MOI) of 0.1 with single phage suspensions of phSE-2 and phSE-5 provided the best results, as it decreased by ~ 1.3 and 1.7 log CFU/g, respectively, the concentration of Salmonella spp. after a 4 h treatment. At a MOI of 0.1, the rate of inactivation with single phage suspensions was higher when compared with the results obtained using the phage cocktail. However, in naturally contaminated cockles treated in static seawater with single phage suspensions and phage cocktail phSE-2/phSE-5, similar decreases in cultivable bacteria concentration (~ 0.7–0.9 log CFU/g) were achieved after 6 h of treatment. When artificially contaminated cockles were depurated with phage phSE-5 in a recirculated seawater system (mimicking industrial depuration conditions), a 0.9 and 2.0 log CFU/g reduction of Salmonella spp. was reached after 4 and 6 h treatment. Once the depuration process was performed without phage, a 6 h treatment was needed to obtain a 1.1 log CFU/g reduction of Salmonella spp. Results indicated that combining phage biocontrol with depuration procedures enhance bivalve microbial safety for human consumption by improving decontamination efficiency, proving that this technology can be transposed to the bivalves industry. Moreover, this approach also displays the advantage of reducing the time required for depuration and consequently its associated costs.     

Microbial safety considerations of flooding in primary production of leafy greens: A case study

This study evaluated the effects of a flood event, floodplain and climatic parameters on microbial contamination of leafy greens grown in the floodplains. Additionally, correlations between pathogenic bacteria and levels of indicator microorganisms have been also determined. To diagnose the microbial contamination after the flood event, sampling was carried out in weeks 1, 3, 5 and 7 after the flooding in four flooded lettuce fields. To assess the impact of flooding on the microbial contamination of leafy greens, indicator microorganisms (coliforms, Escherichia coli and Enterococcus) and pathogenic microorganisms (Salmonella spp., VTEC (E. coli O157:H7 and other verocytotoxin producing E. coli, O26, O103, O111, O145) and Listeria monocytogenes) were evaluated. Irrigation water, soil and lettuce samples showed levels of coliforms and E. coli higher than 5 and 3 log cfu/g or 100 mL, respectively when sampled 1 week after flooding. However, bacterial counts drastically declined three weeks after the flooding. Climatic conditions after flooding, particularly the solar radiation (6–8 MJ/m²), affected the survival of bacteria in the field. L. monocytogenes was not detected in lettuce samples, except for 2 samples collected 3 weeks after the flooding. The presence of Salmonella was detected in irrigation water, soil and lettuce by multiplex PCR one week after the flooding, but only 2 samples of soil and 1 sample of water were confirmed by colony isolation. Verotoxigenic E. coli was detected in soil and lettuce samples by multiplex PCR. Therefore, the implication of flood water as the source of VTEC contamination of soil and lettuce was not clear. E. coli counts in irrigation water were positively correlated with those in lettuce. A significant correlation (P < 0.005) was found between the presence of pathogens and E. coli counts, highlighting a higher probability of detection of pathogens when high levels of E. coli are found. The results obtained in the present study confirm previous knowledge which defined flooding as a main risk factor for the microbial contamination of leafy greens.     

Identification of cultivable lactic acid bacteria isolated from Algerian raw goat's milk and evaluation of their technological properties

One hundred and fifty-eight strains of lactic acid bacteria isolated from Algerian raw goat's milk were identified and technologically characterized. Five genera were found: Lactobacillus (50.63%), Lactococcus (25.94%), Streptococcus (14.56%), Leuconostoc (7.59%) and Pediococcus (1.26%). The predominant species were Lactococcus lactis (32 strains), Streptococcus thermophilus (23 strains), Lactobacillus bulgaricus (19 strains), Lb. helveticus (16 strains) and Lb. plantarum (14 strains).Approximately 39% of the lactic acid bacteria isolated produced more than 0.6% lactic acid (w/v) after 18 h of incubation, and belonged to the Lactococcus and Lactobacillus genera. The highest proteolytic activity was approximately 3 mg tyrosine l⁻¹ for mesophilic strains and nearly 5 mg tyrosine l⁻¹ for thermophilic lactobacilli after 72 h. High aromatic activity (more than 0.8 mg diacetyl l⁻¹ after 16 h) was detected in 14% of the strains.Nine strains were used to make dairy products (a yoghurt-like product and Edam-type cheese) on a pilot scale in the laboratory. The best-liked organoleptic characteristics were noted in a yoghurt produced with a mixed culture made up of S. thermophilus (strain 16TMC+) and Lb. helveticus (strain 20TMC) and in a cheese made with a starter composed of Lc. lactis subsp. lactis (strain 10MCM) and L. lactis subsp. lactis (V.P. +) (strain 19MCM).     

Combined natural antimicrobial treatments (EDTA,lysozyme, rosemary and oregano oil) on semi cooked coated chicken meat stored in vacuum packages at 4 °C: Microbiological and sensory evaluation

The present study examined the effect of natural antimicrobials: Ethylenediaminetetraacetate (EDTA), lysozyme, rosemary and oregano oil and their combinations, on the shelf-life of semi cooked coated chicken fillets stored under vacuum packaging (VP), at 4 ± 0.5 °C for a period of 18 days. The treatments of semi cooked coated chicken fillets examined in the present study were the following: Air-packaged (A, control samples), vacuum-packaged (VP), VP with EDTA–lysozyme solution 1.50% w/w, (VP + EL), VP with rosemary oil 0.20% v/w, (VP + R), VP with oregano oil 0.20% v/w, (VP + O), VP with EDTA–lysozyme solution and rosemary oil (VP + EL + R) and finally VP with EDTA–lysozyme and oregano oil (VP + EL + O). The shelf-life of the samples was determined using both microbiological and sensory analyses. Among the antimicrobial combinations examined in the present study, the treatments VP + EL + R and VP + EL + O were the most effective against the growth of Gram-negative, Gram-positive bacteria, and to a lesser extent on yeasts. Based on both microbiological (TVC data) and sensory (taste attribute) analyses, treatments: VP and VP + O gave a shelf life extension of 6 days, whereas treatments VP + EL + R and VP + EL + O produced a shelf-life extension of 7–8 days, as compared to the control samples.Industrial RelevanceThe present research has highlighted the use of natural antimicrobial treatment combinations, including: EDTA, lysozyme, rosemary and oregano oil and their combinations, in the extension of shelf-life of semi cooked coated chicken fillets stored under vacuum packaging at 4 °C for a period of 18 days. Establishing, the determination of the shelf-life of fresh poultry and products represents a challenge for food companies as poultry meat has a short shelf-life, which causes substantial practical problems for its distribution. Therefore, knowledge of natural preservatives, that can be used as alternatives to chemical additives, that could extend the products' shelf life can have an important economic feedback by reducing losses attributed to spoilage and by allowing the products to reach distant and new markets. This study has shown that combinations of natural antimicrobials can extend the shelf-life of the product.     

Survival of Salmonella Enteritidis PT 30 on inoculated almond kernels in hot water treatments

Almonds are blanched by exposure to hot water or steam-injected water to remove the pellicle (skin) from the kernel. This study evaluated the survival of Salmonella Enteritidis PT 30, Salmonella Senftenberg 775W and Enterococcus faecalis on whole raw almond kernels exposed to hot water. Whole, inoculated (7 to 9 log CFU/g) Nonpareil almonds (40 g) were submerged in 25 L of water maintained at 60, 70, 80 and 88 °C. Almonds were heated for up to 12 min, drained for 2 s, and transferred to 80 mL of cold (4 °C) tryptic soy broth. Almonds in broth were stomached at high speed for 2 min, serially diluted, plated onto tryptic soy and bismuth sulfite agars (Salmonella) or bile esculin agar (Enterococcus) and incubated at 37 °C for 24 and 48 h, respectively. D values of 2.6, 1.2, 0.75 and 0.39 min were calculated for exposure of S. Enteritidis PT 30 to water at 60, 70, 80 and 88 °C, respectively; the calculated z value was 35 C°. D values determined for Salmonella Senftenberg 775W and E. faecalis at 88 °C were 0.37 and 0.36 min, respectively. Neither Salmonella serovar could be recovered by enrichment of 1-g samples after almonds inoculated at 5 log CFU/g were heated at 88 °C for 2 min. These data will be useful to validate almond industry blanching processes.     

Diet-induced changes in alginate- and laminaran-fermenting bacterial levels in the caecal contents of rats

Brown algae contain soluble polysaccharides, such as alginic acid, fucoidan and laminaran. To assess the induction of dietary fiber-fermenting bacteria in the intestine, rats were fed diet containing no dietary fiber (control) or 2% w/w of the polysaccharides for 2 weeks. The levels of dietary fiber-fermenting bacteria in caecal contents were determined using decimal dilution culture containing 1% w/v of the fibers. Caecal microbiota in the rats was analyzed using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). In the culture method, 4–9 log viable cells/g caecal content of alginate-fermenting bacteria was detected in rats fed alginate, while this was not detected in rats fed the control diet. Although laminaran-fermenting bacteria were detected in control rats (4–9 log viable cells/g), the level observed in rats fed laminaran was 8 or 9 log viable cells/g. On the other hand, fucoidan-fermenting bacteria were not detected in rats fed fucoidan. DGGE analysis showed laminaran administration increased the diversity of bacterial bands. Clostridium spp. and Parabacteroides distasonis were detected as typical species in rats fed alginate and laminaran. The results indicate that the intake of soluble fermentable fibers in edible brown algae can alter the intestinal microbiota and its fermentation capacity.     

Investigation of the selective bactericidal effect of several decontaminating solutions on bacterial biofilms including useful,spoilage and/or pathogenic bacteria

The aim of this work was to investigate the selective bactericidal effect of several decontaminating solutions on some spoilage, pathogenic and useful bacteria isolated from a traditional meat workshop.Fourteen decontaminating solutions, i.e., acid, alkaline, osmotic, biocide solutions or their combinations were tested on five bacterial species grown as monospecies biofilms. The solution made of monolaurin (0.075% w/v) and acetic acid at pH 5.4 was the most selective decontaminating solution. It reduced by only 0.2 and 0.4 log Lactobacillus spp. and Staphylococcus carnosus, whereas Pseudomonas fluorescens, Pseudomonas putida and Listeria monocytogenes exhibited reductions of 3.7, 3.2 and 4.2 log, respectively. The acetic solution (pH 5.4) and the solution containing monolaurin (0.075% w/v) and sodium sulfate (12% w/v) were also selective. But their bactericidal effects on Pseudomonas species were relatively small.Four selected solutions were then applied to seven bacterial species grown as multispecies biofilms. The mixture solution of monolaurin (0.075% w/v) and acetic acid at pH 5.4 showed again the best selectivity. Finally, lowering the pH of the acetic solution from 5.4 to 5.2 increased the selective decontamination.     

Effect of mild heat pre-treatment with alkaline electrolyzed water on the efficacy of acidic electrolyzed water against Escherichia coli O157:H7 and Salmonella on Lettuce

Cut lettuce dip-inoculated with Escherichia coli O157:H7 and Salmonella was treated with alkaline electrolyzed water (AlEW) at 20°C for 5 min, and subsequently washed with acidic electrolyzed water (AcEW) at 20°C for 5 min. Pre-treatment with AlEW resulted in an approximate 1.8 log₁₀ cfu/g reduction of microbial populations, which was significantly (p⩽0.05) greater than microbial reductions resulting from other pre-treatment solutions, including distilled water and AcEW. Repeated AcEW treatment did not show a significant bacterial reduction. Mildly heated (50°C) sanitizers were compared with normal (20°C) or chilled (4°C) sanitizers for their bactericidal effect. Mildly heated AcEW and chlorinated water (200 ppm free available chlorine) with a treatment period of 1 or 5 min produced equal reductions of pathogenic bacteria of 3 log₁₀ and 4 log₁₀ cfu/g, respectively. The procedure of treating with mildly heated AlEW for 5 min, and subsequent washing with chilled (4°C) AcEW for period of 1 or 5 min resulted in 3–4 log₁₀ cfu/g reductions of both the pathogenic bacterial counts on lettuce. Extending the mild heat pre-treatment time increased the bactericidal effect more than that observed from the subsequent washing time with chilled AcEW. The appearance of the mildly heated lettuce was not deteriorated after the treatment. In this study, we have illustrated the efficacious application of AlEW as a pre-wash agent, and the effective combined use of AlEW and AcEW.     

Determination of the efficacy of ultrasound in combination with essential oil of oregano for the decontamination of Escherichia coli on inoculated lettuce leaves

Recent outbreaks related to fresh produce have shown that there is a need to develop new efficient and effective decontamination technologies that protect consumers' safety. Ultrasound and assisted ultrasound, i.e., the combination of ultrasound with another decontamination technology has been shown to be effective against bacteria. In this study equal surfaces of free-bacteria of Romaine lettuce were inoculated with Escherichia coli O157:H7 NCTC 12900. Leaves were then treated with an ultrasound probe system (26 kHz, 90 μm, 200 W, 14 mm Ø). Same processing time (300 s) was applied with continuous and pulsed modes of: (i) 10 s on/6 s off, (ii) 5 s on/5 s off and (iii) 2 s on/8 s off. Thus, total treatment durations were 5, 8, 10 and 25 min. Moreover, concentrations of essential oil (i.e. 0.010% v/v, 0.014% v/v. 0.018% v/v, 0.022% v/v and 0.025% v/v) of oregano were tested, operating with continuous and 2 s on/8 s off pulsed mode. The structure of treated samples was also analysed by SEM and light microscopy. Continuous ultrasound treatments led to a reduction of 2.65 ± 0.23 log CFU/cm² of E. coli on the lettuce. No significant differences were found among the tested pulsed and continuous modes. In addition no significant differences were found between injured and no-injured cells among all the applied treatments on the leaves of the lettuce. Application of the different concentrations of EO alone, at the levels mentioned previously reduced the bacteria on the surface of the lettuce. Less than 2 logs of total inactivation (on the lettuce and the treated water) were achieved when different concentrations of EO were tested alone. Assisted ultrasound enhanced the levels of microbial reduction on the surface of the lettuce at concentrations higher than 0.010% (v/v) of oregano EO. Significant differences were found at 0.018%, 0.022% and 0.025% (v/v) both in continuous and pulsed US modes when compared with samples treated only with US. Same concentrations of EO combined with continuous or pulsed mode of US reduced the level of E. coli in water below the limit of detection. When continuous or pulse mode of US was combined with 0.025% (v/v) of EO of oregano the result was synergetic. Images reported neither structural differences nor damage of the leaves among treated samples and controls. Concluding, the effectiveness of the assisted ultrasound process was dependent on the processing time rather than on the different configurations (continuous or on/off) or the total treatment duration. Furthermore, EO combined with US could work synergistically on enhancing the inactivation of the tested bacteria.     

Physical and antibacte rial properties of alginate-based edible film incorporated with garlic oil

Antibacterial alginate-based edible film has been studied by incorporation of garlic oil as a natural antibacterial agent. Initially, 0.1% v/v garlic oil was tested in in vitro experiments against some food pathogenic bacteria. The presence of 0.1% v/v garlic oil in the nutrient broth decreased viable cell counts for Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Bacillus cereus by 2.28, 1.24, 4.31 and 5.61 log cycles, respectively after 24 h incubation. Meanwhile, an increased cell population occurred on all accompanying controls. Antimicrobial alginate films were prepared by incorporating garlic oil up to 0.4% v/v. They were characterized for antibacterial activity, mechanical and physical properties. The edible film exhibited antibacterial activity against Staphylococcus aureus and B. cereus among bacteria tested by using agar diffusion assay. Tensile strength and elongation at break were significantly (p < 0.05) changed by incorporation of garlic oil at 0.3% and 0.4% v/v, respectively. Water vapor permeability decreased significantly (p < 0.05) with 0.4% v/v garlic oil incorporation, whereas total color difference remained same until 0.4% v/v. These results revealed that garlic oil has a good potential to be incorporated into alginate to make antimicrobial edible film or coating for various food applications.