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.     

Antimicrobial activity of Pistacia lentiscus and Satureja montana essential oils against Listeria monocytogenes CECT 935 using laboratory media: Efficacy and synergistic potential in minced beef

The aim of this study was to optimize the antimicrobial efficacy of plant essential oils (EOs) for control of Listeria monocytogenes (L. monocytogenes) serovar 4b CECT 935 using laboratory media and minced beef stored at 5 ± 1 °C. Commercial EOs obtained from leave parts of Mediterranean Pistacia lentiscus (P. lentiscus) and Satureja montana (S. montana) were analyzed by gas chromatography–mass spectrometry (GC–MS). The main components of EOs obtained were β-myrcene (15.18%) and carvacrol (29.19%), respectively for P. lentiscus and S. montana. The in vitro antimicrobial activity of both EOs was evaluated against L. monocytogenes using the agar diffusion technique, the minimum inhibitory concentrations (MIC) were also determined against the same microorganism using the broth microdilution method. According to the diameters of inhibition, S. montana EO had more antibacterial effects than that from P. lentiscus. MICs showed a range of 0.03 and 0.10% (vol/vol) respectively for S. montana and P. lentiscus. S. montana and P. lentiscus EOs were added respectively in minced beef (twofold MIC values) at 0.06 and 0.20%, experimentally inoculated with L. monocytogenes at a level of 3 × 10⁵ CFU/g and stored at 5 ± 1 °C during one week. S. montana EO was the more effective (P < 0.05) against target bacteria. P. lentiscus EO also demonstrated antibacterial effect against the same bacterium. EO combinations were also investigated in minced beef and P. lentiscus combined with S. montana had synergistic effects. This work shows that the combined EOs might be more effective against L. monocytogenes when applied to minced beef at the ratio of 1/1 to 2/2 according to the MIC values. Sensory evaluation revealed that minced beef treated with EOs was acceptable by panelists at the levels used.     

Antifungal activity and mechanism of action of carvacrol and thymol against vineyard and wine spoilage yeasts

Antimicrobial activity of carvacrol and thymol against natural yeast flora of the grapes and yeasts known to cause wine spoilage was examined. Carvacrol and thymol exhibited comparable or better antifungal activity than potassium metabisulphite, commercially used wine preservative, against the natural yeast flora and spoilage yeasts. The antifungal activity for both the compounds was better at pH 3.5 than pH 6.5. Addition of carvacrol and thymol (64 μg/mL) in red wine resulted in inhibition of growth of the spoilage yeasts. Carvacrol and thymol exerted their antimicrobial action through membrane damage, leakage of cytoplasmic content and ergosterol depletion. In conclusion, carvacrol and thymol holds promise as a potential natural preservative for the control of wine spoilage.     

Enhanced antibacterial effectiveness of essential oils vapors in low pressure environment

Due to their antimicrobial activity, essential oils (EOs) have potential to alternate conventional food preservatives. Relatively high doses of EOs necessary for microbial growth inhibition indicate that they should be used in combination with other preservation techniques rather than alone. Therefore, new combinations of preservative methods with EOs are still investigated. In our study, oregano, clove, cinnamon, and lemongrass EO vapors were tested in vitro in atmospheric and low pressure against Escherichia coli and Salmonella enteritidis at different times of treatment ranging from 5 min to 4 h. Combination of EO-low pressure shortened up to 48 times the time necessary for total inhibition of microorganism growth compared to the same treatment in atmospheric pressure. Minimal inhibitory times of EOs vapors ranged mostly from 15 to 60 min in low pressure and were equal to or more than 4 h in atmospheric pressure. Possible decrease of MICs of EOs in low pressure was also investigated. Microorganisms demonstrated increased susceptibility to oregano, lemongrass and cinnamon EOs in low pressure e.g. the MIC of cinnamon vapors for S. enteritidis decreased from 512 μL/L to 128 μL/L.     

Influence of emulsifier type on the antifungal activity of cinnamon leaf,lemon and bergamot oil nanoemulsions against Aspergillus niger

Only exiguous data are currently available on the antifungal properties of essential oil (EO) nanoemulsions against spore-forming microorganisms. The aim of this work is to develop physically stable nanoemulsion-based delivery systems for different EOs (cinnamon leaf, lemon, and bergamot), to exploit their antifungal properties against Aspergillus niger. The inhibition of mycelial radial growth and spore germination were used as indicators of antifungal activity of the nanoemulsions, which were prepared at 3 wt% EO, using non-ionic Tween 80 (T80) or anionic whey protein isolate (WPI) (1 wt%) as emulsifiers, and sunflower oil (1 wt%) as ripening inhibitor. The nanoemulsions were physically stable over seven days of accelerated aging at 35 °C.The minimal inhibitory concentration of free cinnamon leaf and of both citrus EOs were 0.35 and 5.50 μg/g, respectively. The encapsulation of cinnamon leaf EO in nanoemulsions significantly enhanced the inhibiting effect against A. niger mycelial growth and spore germination, with respect to the free EO. In contrast, for citrus EOs, the encapsulation in nanoemulsions generally decreased the antifungal activity, likely because of the nanoemulsion acting as a hydrophobic sink for the main constituents of citrus EOs. The emulsifier played a fundamental role in the resulting antifungal activity, with WPI-based nanoemulsions being more effective in inhibiting the mycelial growth and the spore germination of A. niger than T80-based ones. The antifungal action was correlated to the morphological alterations observed in A. niger, such as the loss of cytoplasm in fungal hyphae and hyphal tip. The results of this study show the importance of nanoemulsions design in the development of efficient and stable natural antifungal agents for food applications.     

Antibacterial activity of plant essential oils and extracts: The role of thyme essential oil,nisin, and their combination to control Listeria monocytogenes inoculated in minced fish meat

Food poisoning caused by Listeria monocytogenes leads to a 30% rate of mortality among patients. The antibacterial activity of cinnamon, thyme, and rosemary essential oils (EOs) and shallot and turmeric extracts was tested against L. monocytogenes using agar well and disc diffusion techniques. Results showed that thyme EO had the highest antimicrobial activity, followed by cinnamon and rosemary EOs, respectively. The antilisterial activity of thyme EO at 0.4%, 0.8%, and 1.2% levels, nisin at 500 or 1000 IU/g level, and their combination against L. monocytogenes was examined in minced fish samples. The antilisterial properties of nisin were also investigated in cooked minced fish treatments. Nisin at 500 or 1000 IU/g in the minced fish meat demonstrated bacteriostatic activity against L. monocytogenes. The use of thyme EO at 0.8% and 1.2% reduced the L. monocytogenes viable count below 2 log cfu/g after 6 days. Furthermore, simultaneous use of thyme EO at 0.8% and 1.2%, and nisin at 500 or 1000 IU/g level, reduced the L. monocytogenes viable count below 2 log cfu/g after the second day of storage. The antilisterial activity of nisin in the cooked minced fish samples was slightly stronger than that of the raw group.     

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.     

Combined analytical and microbiological tools to study the effect on Aspergillus flavus of cinnamon essential oil contained in food packaging

Cinnamon essential oil has been used for centuries to protect food from microbiological infection, and in the last ten years cinnamon essential oil is also incorporated into food packaging materials as antimicrobial agent. However, very little is known about the real effect that it has on the microorganism cells. This study combines analytical and microbiological tools to elucidate cell damage produced on Aspergillus flavus. First, antifungal activity of cinnamon essential oil was evaluated at 10³,10⁴, 10⁵ and 10⁶ CFU/mL. Minimal Inhibitory Concentration (MIC) and Minimal Fungicidal Concentration (MFC) were determined by macrodilution in direct contact with the mold. A strong activity was obtained, with a MIC of 0.05–0.1 mg/mL, and a MFC of 0.05–0.2 mg/mL, both ranges depending on the initial fungal suspensions.Polyethylene terephthalate films containing cinnamon essential oil were tested in vapor phase, without direct contact with the mold. Active PET started showing activity at 2% CIN EO load and produced total inhibition at 4% CIN EO. SEM and FTIR were used to study the cell damage on the mold exposed to the cinnamon essential oil. Evident damage and a strong decrease in sporulation were found by SEM, while biochemical changes in conidia could be suggested from the FTIR spectra analysis. Two deposition techniques were used to prepare the samples for FTIR. The results obtained are shown and discussed.     

Growth inhibition and morphological alterations of Fusarium verticillioides by cinnamon oil and cinnamaldehyde

Fusarium verticillioides is a filamentous fungus and a widely distributed pathogen having the ability to infect and cause destruction in economically important crops and grains by producing fumonisin mycotoxins. In the present study, the inhibitory effect of cinnamon, citral, Litsea cubeba oil, clove, eucalyptus, anise, spearmint and camphor oils on F. verticillioides was investigated, and cinnamon oil proves to be the most effective in inhibition. The antifungal effect of cinnamon oil was studied with special reference to its mechanism of inhibition of F. verticillioides growth at the morphological and ultrastructural levels. For F. verticillioides, the minimal inhibitory concentrations (MICs) of cinnamon oil (85% cinnamaldehyde), natural cinnamaldehyde (95%), and synthetic cinnamaldehyde (99%) were 60, 50, and 45 μL/L, respectively. The antifungal activity of cinnamon oil was proportional to its cinnamaldehyde concentration. Scanning electron microscopy and transmission electron microscopy of F. verticillioides exposed to MIC of cinnamaldehyde showed irreversible deleterious morphological and ultrastructural alterations, such as lack of cytoplasmic contents, loss of integrity and rigidity of the cell wall, plasma membrane disruption, mitochondrial destruction, folding of the cell. These modifications induced by cinnamaldehyde may be due to its interference with enzymatic reactions of cell wall synthesis, thus affecting the morphogenesis and growth of the fungus. These results further emphasized the toxicity of cinnamon oil against F. verticillioides attacking grains, and that cinnamon oil could be safely used as an alternative to chemical fungicides during grain storage and in the field.     

Microbiological quality of fresh vegetables and fruits sold in Singapore

The aim of this study was to characterise the microbiological quality of selected common fresh vegetables and fruits commercially sold in Singapore in order to provide insight into any potential health hazards associated with consumption of these commodities. A total of 125 samples, collected from major supermarkets and local markets, were tested for aerobic mesophilic and psychrotrophic bacterial counts. One hundred samples were analysed for enumeration of yeasts and moulds, enumeration of coliforms and detection of Escherichia coli O157:H7 and Salmonella spp. Aerobic mesophilic counts ranged from 1.6 to 9.1 log cfu/g, with the lowest and the highest counts recorded for orange and bean sprouts, respectively. The highest level of coliforms was found in bean sprouts and fresh-cut salad, with 50% of samples containing more than 5 log cfu/g. Like coliform counts, the highest counts of yeasts and moulds were obtained in bean sprouts and fresh-cut salads. Fresh-cut salads also had the highest mean psychrotrophic plate count of 4.9 log cfu/g. Although no E. coli O157:H7 or Salmonella spp. was detected in the fruits and vegetables analysed in this study, high bacterial counts, especially in bean sprouts and fresh-cut salad, imply that effective control measures should be implemented to improve the microbiological quality of fresh produce sold in Singapore.     

Chemical composition and in vitro antimicrobial,antifungal and antioxidant properties of essential oils obtained from some herbs widely used in Portugal

The aim of this study was determine (i) the chemical composition (ii) the antimicrobial activity (antibacterial and antifungal) and (iii) the antioxidant activity by means of four different antioxidant tests (DDPH, FIC, FRAP and TBARS) of the EOs of three aromatic herbs, Coriander (Coriandrum sativum), celery (Apium graveolens) and bush-basil (Ocimum minimum) widely used in Portugal.There is a great variability of the compounds presented in the three tested essential oils. Bush-basil EO had the highest total phenolic content (794.9 mg GAE/L) while coriander EO had the lower total phenolic content (52.3 mg GAE/L). Since bush-basil had the highest TPC it was expected to present a very high antioxidant profile, which was verified in 3 of the 4 assays (DPPH inhibition of 95.9%; FRAP values of 2.7 mmol Trolox/L; TBARS inhibition of 87.2%); coriander, despite the low TPC showed the highest inhibition in the FIC assay (94.1%).The bush-basil EO showed the highest antimicrobial activity, with MIC ranging between 0.6 and 5 μL/mL against bacteria and 0.04–2.5 μL/mL against yeasts. Both celery and coriander EO had a very similar antimicrobial activity against all the tested strains. The antifungal activity was higher in the bush-basil EO against Mucor racemosus and Penicillium chrysogenum since it was the only EO that showed growth inhibition on all the tested concentrations. Alternaria alternata showed great resistance against all the tested essential oils.     

Studies on antibacterial activity and antibacterial mechanism of a novel polysaccharide from Streptomyces virginia H03

A novel polysaccharide isolated from the broth of Streptomyces virginia H03 exhibited strong antibacterial activities on food spoilage and food poisoning microorganisms such as Staphylococcus aureus, Bacillus subtilis, Listeria monocytogenes, Escherichia coli, Zygosaccharomyces bailii and Candida utilis. The minimal inhibitory concentrations of the polysaccharide determined by the double broth dilution method were 15.6, 31.3, 31.3, 31.3, 125 and 125 (μg/ml) against the microorganisms mentioned above, respectively. The possible targets of the polysaccharide in bacteria might be cell wall, cytoplasmic membrane and DNA as indicated by electron microscopy, leakage of protein, cytoplasmic membrane permeability and DNA binding, respectively. Moreover, the antibacterial activity remained unchanged after being treated at 100 °C for 10 min, which indicated that the polysaccharide had a good heat-stability. In addition, it was safe according to mouse toxicity. All of these suggested that the polysaccharide might be used as a potential antimicrobial in food.     

Radiosensitization of Aspergillus niger and Penicillium chrysogenum using basil essential oil and ionizing radiation for food decontamination

Stored products may be contaminated by pathogenic fungi such as Fusarium, Aspergillus and Penicillum. Fumigation with plant essential oil (EO) and irradiation treatment are options to control spoilage organisms. Basil essential oil and irradiation were tested alone and in combination for their antifungal effects in rice. Minimum Inhibitory Concentration (MIC) of basil EO was found to be 0.1% (v/v) against Aspergillus niger and Penicillium chrysogenum after 48 h. Radiosensitization of A. niger and P. chrysogenum in presence of 1% or 2% (v/v) basil EO was evaluated in vitro and in situ. At 1 and 2% of basil EO, the in vitro D₁₀ value was 0.43 and 0.31 kGy respectively for A. niger and 0.44 and 0.34 kGy respectively for P. chrysogenum. In inoculated rice, D₁₀ values for controls (sample without EO) were 0.67 and 0.63 kGy for A. niger and P. chrysogenum respectively, and the values were decreased at higher EO concentrations. For A. niger, a 2% (v/wt) basil EO alone caused a 0.42 to 1.18 log reduction on days 1 and 14 respectively, whereas treatment with 2 kGy radiation alone caused a 2.18 log reduction. The combined treatments resulted in a 4.6 log reduction of A. niger after 14 days of storage. For P. chrysogenum, 2% basil EO alone caused a 0.76 and a 1.12 log reduction on days 1 and 14 respectively, whereas a 2 kGy radiation dose caused a 2.41 log reduction. The combined treatments resulted in a 5.0 log reduction of P. chrysogenum after 14 days of storage. The findings demonstrated the potential of basil EO as antifungal agent and its efficacy to increase the radiosensitivity of A. niger and P. chrysogenum during irradiation treatment.     

Antimicrobial activity of natural antimicrobial substances against spoilage bacteria isolated from fresh produce

The aim of this study was to investigate the efficacy of natural antimicrobial substances for inhibiting vegetable spoilage bacteria. Natural antimicrobial compounds (carvacrol, thymol, eugenol, cinnamic acid, nisin, and chitosan), organic acids (acetic acid and lactic acid), and chemical sanitizers (sodium hypochlorite and chlorine dioxide) were evaluated for their antibacterial activities, as single and combination treatments, against 15 spoilage bacteria isolated from vegetables, using the agar disc diffusion and broth dilution methods. Carvacrol, thymol, and eugenol showed strong inhibitory effects compared to those of the other antimicrobial substances, and their average minimum inhibitory concentration (MIC) values against 15 spoilage bacteria were 167, 648, and 168 μg/ml, respectively. When they were combined, four kinds (carvacrol + thymol, carvacrol + eugenol, thymol + eugenol, and carvarol + thymol + eugenol) of the combination formulas showed higher antibacterial effect than others against spoilage bacteria, with average MIC values of 47, 43, 59, and 42 μg/ml, respectively. However, two combinations (carvacrol + thymol, and carvacrol + thymol + eugenol) showed the strongest inhibitory effects against bacteria in fresh vegetables among all treatments. These results could be used for the development of new sanitation or preservation methods to improve freshness and to extend the shelf-life of fresh produce.     

Inactivation of Escherichia coli O157:H7 and spoilage yeasts in germicidal UV-C-irradiated and heat-treated clear apple juice

The decimal reduction times (D) of individual and composited Escherichia coli O157:H7 or spoilage yeasts in UV-C irradiated and heated (55 °C) clear apple juices (pH 3.68, 12.5 °Brix) were determined. Spoilage yeasts (D = 6.38-11.04 min) were found to be generally more UV-C resistant than E. coli O157:H7 (D = 0.5-2.76 min), while the opposite was observed in terms of thermal resistance (E. coli D=0.9-4.43 min; yeast D = 0.03-6.10 min). All spoilage yeast proliferated in the untreated juice (25 °C) while all E. coli strains were inactivated. Except for E. coli O157:H7 in UV-C irradiated apple juice, the composited inocula of both pathogenic and spoilage test organisms were less tolerant than the identified most resistant strain or species. The results of this study may be used in identifying appropriate target organisms, as well as the modes of inoculation, in challenge studies and eventually in the establishment and validation of process lethalities for apple juices and similar commodities.     

The antifungal activity of essential oils in combination with warm air flow against postharvest phytopathogenic fungi in apples

Essential oils (EOs) are strong plant-derived antimicrobials. For their efficient use in the agri-food industry, the problems with technology of their application have to be solved. In vitro antifungal activity of cinnamon, oregano, lemongrass and clove essential oils (EOs) was tested by innovative method using EO in combination with warm air flow (WAF). EOs in concentrations from 0.25 to 512 μL/L of air were tested against eleven phytopathogenic fungi. Application of EOs in concentration of 4 and 16 μL/L by WAF method was used for treatment of apples inoculated with Penicillium expansum. Detailed sensory analysis of treated apples was performed. The WAF was more effective compare to standard disc volatilization method (DVM), the average minimum inhibitory concentrations in vitro were 5.6 μL/L during 5 min WAF treatment, compared to 136 μL/L during the DVM 24 h treatment. EOs applied by WAF delayed the incidence and development of P. expansum on apples with minimal adverse effect on their sensory profile. The WAF treatment could be considered for the development of antifungal treatments in the agri-food industry.     

Rutin inhibits mono and multi-species biofilm formation by foodborne drug resistant Escherichia coli and Staphylococcus aureus

Considering the role of biofilm in food spoilage and the food industry, inhibition of biofilm formation by natural agents is expected to be safe and could also enhance the efficacy of other antimicrobial strategies for controlling microbial food spoilage. Plant flavonoids are known for their diverse biological activity including antimicrobial. Therefore, rutin was investigated for its biofilm inhibitory activity at sub-minimum inhibitory concentrations (sub-MICs) values against common foodborne pathogens (Escherichia coli and Staphylococcus aureus). Minimum inhibitory concentrations (MIC) ranged from 400 to 1600 μg/ml against the selected strains. Sub-MICs (1/16 × MIC to 1/2 × MIC) were used to assess the inhibition of biofilm formed by E. coli and S. aureus in microtitre plate assay. Mono strain biofilm formation by Escherichia coli and Staphylococcus aureus was greatly reduced by rutin at their respective 1/2 × MIC. For multi-species (E. coli: and S. aureus) biofilm formation, the reduction in biofilm production was concentration dependent. No significant bacteria mass reduction was recorded for any sub-MIC. SEM images of biofilm inhibition on steel chips confirmed the reduction in number of microcolonies. Exopolysaccharide production responsible for adherence and maturation of biofilms was also significantly (p ≤ 0.05) reduced at respective concentrations of rutin in tested strains. To the best of our knowledge, this is the first study describing the effect of flavonoid, rutin on multi-species biofilms consisting of S. aureus and E. coli. Findings of the study indicate a potential application of rutin in the prevention of biofilm on industrial equipment and food contact surfaces and prevent food contamination and spoilage.     

Evaluation of Zataria multiflora Boiss. essential oil activity against Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes by propidium monoazide quantitative PCR in vegetables

Essential oils (EOs) have long been applied as flavoring agents in foods, and due to their content in antimicrobial compounds, they have potential as natural agents for food preservation. Recently, real-time PCR in combination with PMA has successfully been applied to discriminate between live Escherichia coli O157:H7 and dead bacteria killed by cumin, clove, oregano and cinnamon EOs. In this study, initial experiments were performed in order to elucidate the minimum bactericidal concentration of Zataria multiflora EOs on E. coli O157:H7, Salmonella enterica and Listeria monocytogenes. Thereafter PMA-qPCR was applied in order to selectively quantify life cells within a bacterial population treated with Z. multiflora EO. Inactivation was obtained at EO concentrations of 0.02, 0.035, 0.045 for L. monocytogenes, E. coli O157:H7 and S. enterica, respectively. L. monocytogenes were totally killed in 30 min while it took 1 h 30 min for the gram negative pathogens. As a conclusion Z. multiflora EO has potential as natural food additive or biopreservative since it was able to irreversibly inactivate the three pathogens tested, at lower concentrations than other EOs and short exposition times. In addition, the PMA-qPCR approach proved efficient to selectively detect live pathogenic bacteria in vegetables following inactivation with Z. multiflora EO.     

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.     

Influence of pH and temperature variations on vapor phase action of an antifungal food packaging against five mold strains

An antifungal active food packaging containing cinnamon essential oil has been evaluated under different pH and temperature. Cinnamon essential oil was previously chosen among oregano, clove and their major components cinnamaldehyde, carvacrol and eugenol respectively. Minimal Inhibitory Concentration (MIC) and Minimal Fungicidal Concentration (MFC) were determined by macrodilution method against two strains of Aspergillus flavus as well as Aspergillus niger, Penicillium roqueforti and Penicillium expansum. Despite pH and temperature modified the growth rate of the molds, these variables did not affect the MIC and MFC values. The active food packaging, consisting of Polypropylene films coated with a formula containing 2%–6% cinnamon were produced and evaluated. The antifungal activity was studied against two A flavus, P roqueforti and P. expansum at different pH and temperature. The results highlighted the growth delay caused by the PP 2% in all cases. Total inhibition was obtained with higher amount of cinnamon. This fungicidal action was maintained beyond the 30 days of the experiments. Long-term properties were confirmed after 3 months. The fridge temperature did not hamper the antifungal action of the cinnamon volatile compounds. Finally, all these results demonstrated the high-performance of the antifungal packaging, what guarantee an efficient and durable antifungal protection.